Network Working Group R. Shirey
Request for Comments: 4949 August 2007
FYI: 36
Obsoletes: 2828
Category: Informational

Internet Security Glossary, Version 2

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

RFC Editor Note

   This document is both a major revision and a major expansion of the
   Security Glossary in RFC 2828. This revised Glossary is an extensive
   reference that should help the Internet community to improve the
   clarity of documentation and discussion in an important area of
   Internet technology. However, readers should be aware of the
   following:

   (1) The recommendations and some particular interpretations in
   definitions are those of the author, not an official IETF position.
   The IETF has not taken a formal position either for or against
   recommendations made by this Glossary, and the use of RFC 2119
   language (e.g., SHOULD NOT) in the Glossary must be understood as
   unofficial. In other words, the usage rules, wording interpretations,
   and other recommendations that the Glossary offers are personal
   opinions of the Glossary's author. Readers must judge for themselves
   whether or not to follow his recommendations, based on their own
   knowledge combined with the reasoning presented in the Glossary.

   (2) The glossary is rich in the history of early network security
   work, but it may be somewhat incomplete in describing recent security
   work, which has been developing rapidly.

Abstract

   This Glossary provides definitions, abbreviations, and explanations
   of terminology for information system security. The 334 pages of
   entries offer recommendations to improve the comprehensibility of
   written material that is generated in the Internet Standards Process
   (RFC 2026). The recommendations follow the principles that such
   writing should (a) use the same term or definition whenever the same
   concept is mentioned; (b) use terms in their plainest, dictionary
   sense; (c) use terms that are already well-established in open
   publications; and (d) avoid terms that either favor a particular
   vendor or favor a particular technology or mechanism over other,
   competing techniques that already exist or could be developed.

   1. Introduction ....................................................3
   2. Format of Entries ...............................................4
      2.1. Order of Entries ...........................................4
      2.2. Capitalization and Abbreviations ...........................5
      2.3. Support for Automated Searching ............................5
      2.4. Definition Type and Context ................................5
      2.5. Explanatory Notes ..........................................6
      2.6. Cross-References ...........................................6
      2.7. Trademarks .................................................6
      2.8. The New Punctuation ........................................6
   3. Types of Entries ................................................7
      3.1. Type "I": Recommended Definitions of Internet Origin .......7
      3.2. Type "N": Recommended Definitions of Non-Internet Origin ...8
      3.3. Type "O": Other Terms and Definitions To Be Noted ..........8
      3.4. Type "D": Deprecated Terms and Definitions .................8
      3.5. Definition Substitutions ...................................8
   4. Definitions .....................................................9
   5. Security Considerations .......................................343
   6. Normative Reference ...........................................343
   7. Informative References ........................................343
   8. Acknowledgments ...............................................364

1. Introduction

   This Glossary is *not* an Internet Standard, and its recommendations
   represent only the opinions of its author. However, this Glossary
   gives reasons for its recommendations -- especially for the SHOULD
   NOTs -- so that readers can judge for themselves what to do.

   This Glossary provides an internally consistent and self-contained
   set of terms, abbreviations, and definitions -- supported by
   explanations, recommendations, and references -- for terminology that
   concerns information system security. The intent of this Glossary is
   to improve the comprehensibility of written materials that are
   generated in the Internet Standards Process (RFC 2026) -- i.e., RFCs,
   Internet-Drafts, and other items of discourse -- which are referred
   to here as IDOCs. A few non-security, networking terms are included
   to make the Glossary self-contained, but more complete glossaries of
   such terms are available elsewhere [A1523, F1037, R1208, R1983].

   This Glossary supports the goals of the Internet Standards Process:

   o  Clear, Concise, Easily Understood Documentation

      This Glossary seeks to improve comprehensibility of security-
      related content of IDOCs. That requires wording to be clear and
      understandable, and requires the set of security-related terms and
      definitions to be consistent and self-supporting. Also,
      terminology needs to be uniform across all IDOCs; i.e., the same
      term or definition needs to be used whenever and wherever the same
      concept is mentioned. Harmonization of existing IDOCs need not be
      done immediately, but it is desirable to correct and standardize
      terminology when new versions are issued in the normal course of
      standards development and evolution.

   o  Technical Excellence

      Just as Internet Standard (STD) protocols should operate
      effectively, IDOCs should use terminology accurately, precisely,
      and unambiguously to enable standards to be implemented correctly.

   o  Prior Implementation and Testing

      Just as STD protocols require demonstrated experience and
      stability before adoption, IDOCs need to use well-established
      language; and the robustness principle for protocols -- "be
      liberal in what you accept, and conservative in what you send" --
      is also applicable to the language used in IDOCs that describe
      protocols. Using terms in their plainest, dictionary sense (when
      appropriate) helps to make them more easily understood by

      international readers. IDOCs need to avoid using private, newly
      invented terms in place of generally accepted terms from open
      publications. IDOCs need to avoid substituting new definitions
      that conflict with established ones. IDOCs need to avoid using
      "cute" synonyms (e.g., "Green Book"), because no matter how
      popular a nickname may be in one community, it is likely to cause
      confusion in another.

      However, although this Glossary strives for plain, internationally
      understood English language, its terms and definitions are biased
      toward English as used in the United States of America (U.S.).
      Also, with regard to terminology used by national governments and
      in national defense areas, the glossary addresses only U.S. usage.

   o  Openness, Fairness, and Timeliness

      IDOCs need to avoid using proprietary and trademarked terms for
      purposes other than referring to those particular systems. IDOCs
      also need to avoid terms that either favor a particular vendor or
      favor a particular security technology or mechanism over other,
      competing techniques that already exist or might be developed in
      the future. The set of terminology used across the set of IDOCs
      needs to be flexible and adaptable as the state of Internet
      security art evolves.

   In support of those goals, this Glossary offers guidance by marking
   terms and definitions as being either endorsed or deprecated for use
   in IDOCs. The key words "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are intended to be interpreted the same way as in an
   Internet Standard (i.e., as specified in RFC 2119 [R2119]). Other
   glossaries (e.g., [Raym]) list additional terms that deal with
   Internet security but have not been included in this Glossary because
   they are not appropriate for IDOCs.

2. Format of Entries

Section 4 presents Glossary entries in the following manner:

2.1. Order of Entries

   Entries are sorted in lexicographic order, without regard to
   capitalization. Numeric digits are treated as preceding alphabetic
   characters, and special characters are treated as preceding digits.
   Blanks are treated as preceding non-blank characters, except that a
   hyphen or slash between the parts of a multiword entry (e.g.,
   "RED/BLACK separation") is treated like a blank.

   If an entry has multiple definitions (e.g., "domain"), they are
   numbered beginning with "1", and any of those multiple definitions
   that are RECOMMENDED for use in IDOCs are presented before other
   definitions for that entry. If definitions are closely related (e.g.,
   "threat"), they are denoted by adding letters to a number, such as
   "1a" and "1b".

2.2. Capitalization and Abbreviations

   Entries that are proper nouns are capitalized (e.g., "Data Encryption
   Algorithm"), as are other words derived from proper nouns (e.g.,
   "Caesar cipher"). All other entries are not capitalized (e.g.,
   "certification authority"). Each acronym or other abbreviation that
   appears in this Glossary, either as an entry or in a definition or
   explanation, is defined in this Glossary, except items of common
   English usage, such as "a.k.a.", "e.g.", "etc.", "i.e.", "vol.",
   "pp.", and "U.S.".

2.3. Support for Automated Searching

   Each entry is preceded by a dollar sign ($) and a space. This makes
   it possible to find the defining entry for an item "X" by searching
   for the character string "$ X", without stopping at other entries in
   which "X" is used in explanations.

2.4. Definition Type and Context

   Each entry is preceded by a character -- I, N, O, or D -- enclosed in
   parentheses, to indicate the type of definition (as is explained
   further in Section 3):
   -  "I" for a RECOMMENDED term or definition of Internet origin.
   -  "N" if RECOMMENDED but not of Internet origin.
   -  "O" for a term or definition that is NOT recommended for use in
      IDOCs but is something that authors of Internet documents should
      know about.
   -  "D" for a term or definition that is deprecated and SHOULD NOT be
      used in Internet documents.

   If a definition is valid only in a specific context (e.g.,
   "baggage"), that context is shown immediately following the
   definition type and is enclosed by a pair of slash symbols (/). If
   the definition is valid only for specific parts of speech, that is
   shown in the same way (e.g., "archive").

2.5. Explanatory Notes

   Some entries have explanatory text that is introduced by one or more
   of the following keywords:
   -  Deprecated Abbreviation (e.g., "AA")
   -  Deprecated Definition (e.g., "digital certification")
   -  Deprecated Usage (e.g., "authenticate")
   -  Deprecated Term (e.g., "certificate authority")
   -  Pronunciation (e.g., "*-property")
   -  Derivation (e.g., "discretionary access control")
   -  Tutorial (e.g., "accreditation")
   -  Example (e.g., "back door")
   -  Usage (e.g., "access")

   Explanatory text in this Glossary MAY be reused in IDOCs. However,
   this text is not intended to authoritatively supersede text of an
   IDOC in which the Glossary entry is already used.

2.6. Cross-References

   Some entries contain a parenthetical remark of the form "(See: X.)",
   where X is a list of other, related terms. Some entries contain a
   remark of the form "(Compare: X)", where X is a list of terms that
   either are antonyms of the entry or differ in some other manner worth
   noting.

2.7. Trademarks

   All servicemarks and trademarks that appear in this Glossary are used
   in an editorial fashion and to the benefit of the mark owner, without
   any intention of infringement.

2.8. The New Punctuation

   This Glossary uses the "new" or "logical" punctuation style favored
   by computer programmers, as described by Raymond [Raym]: Programmers
   use pairs of quotation marks the same way they use pairs of
   parentheses, i.e., as balanced delimiters. For example, if "Alice
   sends" is a phrase, and so are "Bill receives" and "Eve listens",
   then a programmer would write the following sentence:

      "Alice sends", "Bill receives", and "Eve listens".

   According to standard American usage, the punctuation in that
   sentence is incorrect; the continuation commas and the final period
   should go inside the string quotes, like this:

      "Alice sends," "Bill receives," and "Eve listens."

   However, a programmer would not include a character in a literal
   string if the character did not belong there, because that could
   cause an error. For example, suppose a sentence in a draft of a
   tutorial on the vi editing language looked like this:

      Then delete one line from the file by typing "dd".

   A book editor following standard usage might change the sentence to
   look like this:

      Then delete one line from the file by typing "dd."

   However, in the vi language, the dot character repeats the last
   command accepted. So, if a reader entered "dd.", two lines would be
   deleted instead of one.

   Similarly, use of standard American punctuation might cause
   misunderstanding in entries in this Glossary. Thus, the new
   punctuation is used here, and we recommend it for IDOCs.

3. Types of Entries

Each entry in this Glossary is marked as type I, N, O, or D:

3.1. Type "I": Recommended Definitions of Internet Origin

   The marking "I" indicates two things:
   -  Origin: "I" (as opposed to "N") means either that the Internet
      Standards Process or Internet community is authoritative for the
      definition *or* that the term is sufficiently generic that this
      Glossary can freely state a definition without contradicting a
      non-Internet authority (e.g., "attack").
   -  Recommendation: "I" (as opposed to "O") means that the term and
      definition are RECOMMENDED for use in IDOCs. However, some "I"
      entries may be accompanied by a "Usage" note that states a
      limitation (e.g., "certification"), and IDOCs SHOULD NOT use the
      defined term outside that limited context.

   Many "I" entries are proper nouns (e.g., "Internet Protocol") for
   which the definition is intended only to provide basic information;
   i.e., the authoritative definition of such terms is found elsewhere.
   For a proper noun described as an "Internet protocol", please refer
   to the current edition of "Internet Official Protocol Standards"
   (Standard 1) for the standardization status of the protocol.

3.2. Type "N": Recommended Definitions of Non-Internet Origin

   The marking "N" indicates two things:
   -  Origin: "N" (as opposed to "I") means that the entry has a non-
      Internet basis or origin.
   -  Recommendation: "N" (as opposed to "O") means that the term and
      definition are RECOMMENDED for use in IDOCs, if they are needed at
      all in IDOCs. Many of these entries are accompanied by a label
      that states a context (e.g., "package") or a note that states a
      limitation (e.g., "data integrity"), and IDOCs SHOULD NOT use the
      defined term outside that context or limit. Some of the contexts
      are rarely if ever expected to occur in an IDOC (e.g., "baggage").
      In those cases, the listing exists to make Internet authors aware
      of the non-Internet usage so that they can avoid conflicts with
      non-Internet documents.

3.3. Type "O": Other Terms and Definitions To Be Noted

   The marking "O" means that the definition is of non-Internet origin
   and SHOULD NOT be used in IDOCs *except* in cases where the term is
   specifically identified as non-Internet.

   For example, an IDOC might mention "BCA" (see: brand certification
   authority) or "baggage" as an example of some concept; in that case,
   the document should specifically say "SET(trademark) BCA" or
   "SET(trademark) baggage" and include the definition of the term.

3.4. Type "D": Deprecated Terms and Definitions

   If this Glossary recommends that a term or definition SHOULD NOT be
   used in IDOCs, then the entry is marked as type "D", and an
   explanatory note -- "Deprecated Term", "Deprecated Abbreviation",
   "Deprecated Definition", or "Deprecated Usage" -- is provided.

3.5. Definition Substitutions

   Some terms have a definition published by a non-Internet authority --
   a government (e.g., "object reuse"), an industry (e.g., "Secure Data
   Exchange"), a national authority (e.g., "Data Encryption Standard"),
   or an international body (e.g., "data confidentiality") -- that is
   suitable for use in IDOCs. In those cases, this Glossary marks the
   definition "N", recommending its use in Internet documents.

   Other such terms have definitions that are inadequate or
   inappropriate for IDOCs. For example, a definition might be outdated
   or too narrow, or it might need clarification by substituting more
   careful wording (e.g., "authentication exchange") or explanations,
   using other terms that are defined in this Glossary. In those cases,

   this Glossary marks the entry "O", and provides an "I" or "N" entry
   that precedes, and is intended to supersede, the "O" entry.

   In some cases where this Glossary provides a definition to supersede
   an "O" definition, the substitute is intended to subsume the meaning
   of the "O" entry and not conflict with it. For the term "security
   service", for example, the "O" definition deals narrowly with only
   communication services provided by layers in the OSIRM and is
   inadequate for the full range of IDOC usage, while the new "I"
   definition provided by this Glossary can be used in more situations
   and for more kinds of service. However, the "O" definition is also
   listed so that IDOC authors will be aware of the context in which the
   term is used more narrowly.

   When making substitutions, this Glossary attempts to avoid
   contradicting any non-Internet authority. Still, terminology differs
   between authorities such as the American Bar Association, OSI, SET,
   the U.S. DoD, and other authorities; and this Glossary probably is
   not exactly aligned with any of them.

4. Definitions

   $ *-property
      (N) Synonym for "confinement property" in the context of the Bell-
      LaPadula model. Pronunciation: star property.

   $ 3DES
      (N) See: Triple Data Encryption Algorithm.

   $ A1 computer system
      (O) /TCSEC/ See: Tutorial under "Trusted Computer System
      Evaluation Criteria". (Compare: beyond A1.)

   $ AA
      (D) See: Deprecated Usage under "attribute authority".

   $ ABA Guidelines
      (N) "American Bar Association (ABA) Digital Signature Guidelines"
      [DSG], a framework of legal principles for using digital
      signatures and digital certificates in electronic commerce.

   $ Abstract Syntax Notation One (ASN.1)
      (N) A standard for describing data objects. [Larm, X680] (See:
      CMS.)

      Usage: IDOCs SHOULD use the term "ASN.1" narrowly to describe the
      notation or language called "Abstract Syntax Notation One". IDOCs
      MAY use the term more broadly to encompass the notation, its

      associated encoding rules (see: BER), and software tools that
      assist in its use, when the context makes this meaning clear.

      Tutorial: OSIRM defines computer network functionality in layers.
      Protocols and data objects at higher layers are abstractly defined
      to be implemented using protocols and data objects from lower
      layers. A higher layer may define transfers of abstract objects
      between computers, and a lower layer may define those transfers
      concretely as strings of bits. Syntax is needed to specify data
      formats of abstract objects, and encoding rules are needed to
      transform abstract objects into bit strings at lower layers. OSI
      standards use ASN.1 for those specifications and use various
      encoding rules for those transformations. (See: BER.)

      In ASN.1, formal names are written without spaces, and separate
      words in a name are indicated by capitalizing the first letter of
      each word except the first word. For example, the name of a CRL is
      "certificateRevocationList".

   $ ACC
      (I) See: access control center.

   $ acceptable risk
      (I) A risk that is understood and tolerated by a system's user,
      operator, owner, or accreditor, usually because the cost or
      difficulty of implementing an effective countermeasure for the
      associated vulnerability exceeds the expectation of loss. (See:
      adequate security, risk, "second law" under "Courtney's laws".)

   $ access
      1a. (I) The ability and means to communicate with or otherwise
      interact with a system to use system resources either to handle
      information or to gain knowledge of the information the system
      contains. (Compare: handle.)

      Usage: The definition is intended to include all types of
      communication with a system, including one-way communication in
      either direction. In actual practice, however, passive users might
      be treated as not having "access" and, therefore, be exempt from
      most requirements of the system's security policy. (See: "passive
      user" under "user".)

      1b. (O) "Opportunity to make use of an information system (IS)
      resource." [C4009]

      2. (O) /formal model/ "A specific type of interaction between a
      subject and an object that results in the flow of information from
      one to the other." [NCS04]

   $ Access Certificate for Electronic Services (ACES)
      (O) A PKI operated by the U.S. Government's General Services
      Administration in cooperation with industry partners. (See: CAM.)

   $ access control
      1. (I) Protection of system resources against unauthorized access.

      2. (I) A process by which use of system resources is regulated
      according to a security policy and is permitted only by authorized
      entities (users, programs, processes, or other systems) according
      to that policy. (See: access, access control service, computer
      security, discretionary access control, mandatory access control,
      role-based access control.)

      3. (I) /formal model/ Limitations on interactions between subjects
      and objects in an information system.

      4. (O) "The prevention of unauthorized use of a resource,
      including the prevention of use of a resource in an unauthorized
      manner." [I7498-2]

      5. (O) /U.S. Government/ A system using physical, electronic, or
      human controls to identify or admit personnel with properly
      authorized access to a SCIF.

   $ access control center (ACC)
      (I) A computer that maintains a database (possibly in the form of
      an access control matrix) defining the security policy for an
      access control service, and that acts as a server for clients
      requesting access control decisions.

      Tutorial: An ACC is sometimes used in conjunction with a key
      center to implement access control in a key-distribution system
      for symmetric cryptography. (See: BLACKER, Kerberos.)

   $ access control list (ACL)
      (I) /information system/ A mechanism that implements access
      control for a system resource by enumerating the system entities
      that are permitted to access the resource and stating, either
      implicitly or explicitly, the access modes granted to each entity.
      (Compare: access control matrix, access list, access profile,
      capability list.)

   $ access control matrix
      (I) A rectangular array of cells, with one row per subject and one
      column per object. The entry in a cell -- that is, the entry for a
      particular subject-object pair -- indicates the access mode that
      the subject is permitted to exercise on the object. Each column is

      equivalent to an "access control list" for the object; and each
      row is equivalent to an "access profile" for the subject.

   $ access control service
      (I) A security service that protects against a system entity using
      a system resource in a way not authorized by the system's security
      policy. (See: access control, discretionary access control,
      identity-based security policy, mandatory access control, rule-
      based security policy.)

      Tutorial: This service includes protecting against use of a
      resource in an unauthorized manner by an entity (i.e., a
      principal) that is authorized to use the resource in some other
      manner. (See: insider.) The two basic mechanisms for implementing
      this service are ACLs and tickets.

   $ access level
      1. (D) Synonym for the hierarchical "classification level" in a
      security level. [C4009] (See: security level.)

      2. (D) Synonym for "clearance level".

      Deprecated Definitions: IDOCs SHOULD NOT use this term with these
      definitions because they duplicate the meaning of more specific
      terms. Any IDOC that uses this term SHOULD provide a specific
      definition for it because access control may be based on many
      attributes other than classification level and clearance level.

   $ access list
      (I) /physical security/ Roster of persons who are authorized to
      enter a controlled area. (Compare: access control list.)

   $ access mode
      (I) A distinct type of data processing operation (e.g., read,
      write, append, or execute, or a combination of operations) that a
      subject can potentially perform on an object in an information
      system. [Huff] (See: read, write.)

   $ access policy
      (I) A kind of "security policy". (See: access, access control.)

   $ access profile
      (O) Synonym for "capability list".

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the definition is not widely known.

   $ access right
      (I) Synonym for "authorization"; emphasizes the possession of the
      authorization by a system entity.

   $ accountability
      (I) The property of a system or system resource that ensures that
      the actions of a system entity may be traced uniquely to that
      entity, which can then be held responsible for its actions. [Huff]
      (See: audit service.)

      Tutorial: Accountability (a.k.a. individual accountability)
      typically requires a system ability to positively associate the
      identity of a user with the time, method, and mode of the user's
      access to the system. This ability supports detection and
      subsequent investigation of security breaches. Individual persons
      who are system users are held accountable for their actions after
      being notified of the rules of behavior for using the system and
      the penalties associated with violating those rules.

   $ accounting See: COMSEC accounting.

   $ accounting legend code (ALC)
      (O) /U.S. Government/ Numeric system used to indicate the minimum
      accounting controls required for items of COMSEC material within
      the CMCS. [C4009] (See: COMSEC accounting.)

   $ accreditation
      (N) An administrative action by which a designated authority
      declares that an information system is approved to operate in a
      particular security configuration with a prescribed set of
      safeguards. [FP102, SP37] (See: certification.)

      Tutorial: An accreditation is usually based on a technical
      certification of the system's security mechanisms. To accredit a
      system, the approving authority must determine that any residual
      risk is an acceptable risk. Although the terms "certification" and
      "accreditation" are used more in the U.S. DoD and other U.S.
      Government agencies than in commercial organizations, the concepts
      apply any place where managers are required to deal with and
      accept responsibility for security risks. For example, the
      American Bar Association is developing accreditation criteria for
      CAs.

   $ accreditation boundary
      (O) Synonym for "security perimeter". [C4009]

   $ accreditor
      (N) A management official who has been designated to have the
      formal authority to "accredit" an information system, i.e., to
      authorize the operation of, and the processing of sensitive data
      in, the system and to accept the residual risk associated with the
      system. (See: accreditation, residual risk.)

   $ ACES
      (O) See: Access Certificate for Electronic Services.

   $ ACL
      (I) See: access control list.

   $ acquirer
      1. (O) /SET/ "The financial institution that establishes an
      account with a merchant and processes payment card authorizations
      and payments." [SET1]

      2. (O) /SET/ "The institution (or its agent) that acquires from
      the card acceptor the financial data relating to the transaction
      and initiates that data into an interchange system." [SET2]

   $ activation data
      (N) Secret data, other than keys, that is required to access a
      cryptographic module. (See: CIK. Compare: initialization value.)

   $ active attack
      (I) See: secondary definition under "attack".

   $ active content
      1a. (I) Executable software that is bound to a document or other
      data file and that executes automatically when a user accesses the
      file, without explicit initiation by the user. (Compare: mobile
      code.)

      Tutorial: Active content can be mobile code when its associated
      file is transferred across a network.

      1b. (O) "Electronic documents that can carry out or trigger
      actions automatically on a computer platform without the
      intervention of a user. [This technology enables] mobile code
      associated with a document to execute as the document is
      rendered." [SP28]

   $ active user
      (I) See: secondary definition under "system user".

   $ active wiretapping
      (I) A wiretapping attack that attempts to alter data being
      communicated or otherwise affect data flow. (See: wiretapping.
      Compare: active attack, passive wiretapping.)

   $ add-on security
      (N) The retrofitting of protection mechanisms, implemented by
      hardware or software, in an information system after the system
      has become operational. [FP039] (Compare: baked-in security.)

   $ adequate security
      (O) /U.S. DoD/ "Security commensurate with the risk and magnitude
      of harm resulting from the loss, misuse, or unauthorized access to
      or modification of information." (See: acceptable risk, residual
      risk.)

   $ administrative security
      1. (I) Management procedures and constraints to prevent
      unauthorized access to a system. (See: "third law" under
      "Courtney's laws", manager, operational security, procedural
      security, security architecture. Compare: technical security.)

      Examples: Clear delineation and separation of duties;
      configuration control.

      Usage: Administrative security is usually understood to consist of
      methods and mechanisms that are implemented and executed primarily
      by people, rather than by automated systems.

      2. (O) "The management constraints, operational procedures,
      accountability procedures, and supplemental controls established
      to provide an acceptable level of protection for sensitive data."
      [FP039]

   $ administrator
      1. (O) /Common Criteria/ A person that is responsible for
      configuring, maintaining, and administering the TOE in a correct
      manner for maximum security. (See: administrative security.)

      2. (O) /ITSEC/ A person in contact with the TOE, who is
      responsible for maintaining its operational capability.

   $ Advanced Encryption Standard (AES)
      (N) A U.S. Government standard [FP197] (the successor to DES) that
      (a) specifies "the AES algorithm", which is a symmetric block
      cipher that is based on Rijndael and uses key sizes of 128, 192,
      or 256 bits to operate on a 128-bit block, and (b) states policy
      for using that algorithm to protect unclassified, sensitive data.

      Tutorial: Rijndael was designed to handle additional block sizes
      and key lengths that were not adopted in the AES. Rijndael was
      selected by NIST through a public competition that was held to
      find a successor to the DEA; the other finalists were MARS, RC6,
      Serpent, and Twofish.

   $ adversary
      1. (I) An entity that attacks a system. (Compare: cracker,
      intruder, hacker.)

      2. (I) An entity that is a threat to a system.

   $ AES
      (N) See: Advanced Encryption Standard.

   $ Affirm
      (O) A formal methodology, language, and integrated set of software
      tools developed at the University of Southern California's
      Information Sciences Institute for specifying, coding, and
      verifying software to produce correct and reliable programs.
      [Cheh]

   $ aggregation
      (I) A circumstance in which a collection of information items is
      required to be classified at a higher security level than any of
      the items is classified individually. (See: classification.)

   $ AH
      (I) See: Authentication Header

   $ air gap
      (I) An interface between two systems at which (a) they are not
      connected physically and (b) any logical connection is not
      automated (i.e., data is transferred through the interface only
      manually, under human control). (See: sneaker net. Compare:
      gateway.)

      Example: Computer A and computer B are on opposite sides of a
      room. To move data from A to B, a person carries a disk across the
      room. If A and B operate in different security domains, then
      moving data across the air gap may involve an upgrade or downgrade
      operation.

   $ ALC
      (O) See: accounting legend code.

   $ algorithm
      (I) A finite set of step-by-step instructions for a problem-
      solving or computation procedure, especially one that can be
      implemented by a computer. (See: cryptographic algorithm.)

   $ alias
      (I) A name that an entity uses in place of its real name, usually
      for the purpose of either anonymity or masquerade.

   $ Alice and Bob
      (I) The parties that are most often called upon to illustrate the
      operation of bipartite security protocols. These and other
      dramatis personae are listed by Schneier [Schn].

   $ American National Standards Institute (ANSI)
      (N) A private, not-for-profit association that administers U.S.
      private-sector voluntary standards.

      Tutorial: ANSI has approximately 1,000 member organizations,
      including equipment users, manufacturers, and others. These
      include commercial firms, governmental agencies, and other
      institutions and international entities.

      ANSI is the sole U.S. representative to (a) ISO and (b) (via the
      U.S. National Committee) the International Electrotechnical
      Commission (IEC), which are the two major, non-treaty,
      international standards organizations.

      ANSI provides a forum for ANSI-accredited standards development
      groups. Among those groups, the following are especially relevant
      to Internet security:
      -  International Committee for Information Technology
         Standardization (INCITS) (formerly X3): Primary U.S. focus of
         standardization in information and communications technologies,
         encompassing storage, processing, transfer, display,
         management, organization, and retrieval of information.
         Example: [A3092].
      -  Accredited Standards Committee X9: Develops, establishes,
         maintains, and promotes standards for the financial services
         industry. Example: [A9009].
      -  Alliance for Telecommunications Industry Solutions (ATIS):
         Develops standards, specifications, guidelines, requirements,
         technical reports, industry processes, and verification tests
         for interoperability and reliability of telecommunications
         networks, equipment, and software. Example: [A1523].

   $ American Standard Code for Information Interchange (ASCII)
      (N) A scheme that encodes 128 specified characters -- the numbers
      0-9, the letters a-z and A-Z, some basic punctuation symbols, some
      control codes that originated with Teletype machines, and a blank
      space -- into the 7-bit binary integers. Forms the basis of the
      character set representations used in most computers and many
      Internet standards. [FP001] (See: code.)

   $ Anderson report
      (O) A 1972 study of computer security that was written by James P.
      Anderson for the U.S. Air Force [Ande].

      Tutorial: Anderson collaborated with a panel of experts to study
      Air Force requirements for multilevel security. The study
      recommended research and development that was urgently needed to
      provide secure information processing for command and control
      systems and support systems. The report introduced the reference
      monitor concept and provided development impetus for computer and
      network security technology. However, many of the security
      problems that the 1972 report called "current" still plague
      information systems today.

   $ anomaly detection
      (I) An intrusion detection method that searches for activity that
      is different from the normal behavior of system entities and
      system resources. (See: IDS. Compare: misuse detection.)

   $ anonymity
      (I) The condition of an identity being unknown or concealed. (See:
      alias, anonymizer, anonymous credential, anonymous login,
      identity, onion routing, persona certificate. Compare: privacy.)

      Tutorial: An application may require security services that
      maintain anonymity of users or other system entities, perhaps to
      preserve their privacy or hide them from attack. To hide an
      entity's real name, an alias may be used; for example, a financial
      institution may assign account numbers. Parties to transactions
      can thus remain relatively anonymous, but can also accept the
      transactions as legitimate. Real names of the parties cannot be
      easily determined by observers of the transactions, but an
      authorized third party may be able to map an alias to a real name,
      such as by presenting the institution with a court order. In other
      applications, anonymous entities may be completely untraceable.

   $ anonymizer
      (I) An internetwork service, usually provided via a proxy server,
      that provides anonymity and privacy for clients. That is, the
      service enables a client to access servers (a) without allowing

      anyone to gather information about which servers the client
      accesses and (b) without allowing the accessed servers to gather
      information about the client, such as its IP address.

   $ anonymous credential
      (D) /U.S. Government/ A credential that (a) can be used to
      authenticate a person as having a specific attribute or being a
      member of a specific group (e.g., military veterans or U.S.
      citizens) but (b) does not reveal the individual identity of the
      person that presents the credential. [M0404] (See: anonymity.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
      in a potentially misleading way. For example, when the credential
      is an X.509 certificate, the term could be misunderstood to mean
      that the certificate was signed by a CA that has a persona
      certificate. Instead, use "attribute certificate", "organizational
      certificate", or "persona certificate" depending on what is meant,
      and provide additional explanations as needed.

   $ anonymous login
      (I) An access control feature (actually, an access control
      vulnerability) in many Internet hosts that enables users to gain
      access to general-purpose or public services and resources of a
      host (such as allowing any user to transfer data using FTP)
      without having a pre-established, identity-specific account (i.e.,
      user name and password). (See: anonymity.)

      Tutorial: This feature exposes a system to more threats than when
      all the users are known, pre-registered entities that are
      individually accountable for their actions. A user logs in using a
      special, publicly known user name (e.g., "anonymous", "guest", or
      "ftp"). To use the public login name, the user is not required to
      know a secret password and may not be required to input anything
      at all except the name. In other cases, to complete the normal
      sequence of steps in a login protocol, the system may require the
      user to input a matching, publicly known password (such as
      "anonymous") or may ask the user for an e-mail address or some
      other arbitrary character string.

   $ ANSI
      (N) See: American National Standards Institute.

   $ anti-jam
      (N) "Measures ensuring that transmitted information can be
      received despite deliberate jamming attempts." [C4009] (See:
      electronic security, frequency hopping, jam, spread spectrum.)

   $ apex trust anchor
      (N) The trust anchor that is superior to all other trust anchors
      in a particular system or context. (See: trust anchor, top CA.)

   $ API
      (I) See: application programming interface.

   $ APOP
      (I) See: POP3 APOP.

   $ Application Layer
      See: Internet Protocol Suite, OSIRM.

   $ application program
      (I) A computer program that performs a specific function directly
      for a user (as opposed to a program that is part of a computer
      operating system and exists to perform functions in support of
      application programs).

   $ architecture
      (I) See: security architecture, system architecture.

   $ archive
      1a. (I) /noun/ A collection of data that is stored for a
      relatively long period of time for historical and other purposes,
      such as to support audit service, availability service, or system
      integrity service. (Compare: backup, repository.)

      1b. (I) /verb/ To store data in such a way as to create an
      archive. (Compare: back up.)

      Tutorial: A digital signature may need to be verified many years
      after the signing occurs. The CA -- the one that issued the
      certificate containing the public key needed to verify that
      signature -- may not stay in operation that long. So every CA
      needs to provide for long-term storage of the information needed
      to verify the signatures of those to whom it issues certificates.

   $ ARPANET
      (I) Advanced Research Projects Agency (ARPA) Network, a pioneer
      packet-switched network that (a) was designed, implemented,
      operated, and maintained by BBN from January 1969 until July 1975
      under contract to the U.S. Government; (b) led to the development
      of today's Internet; and (c) was decommissioned in June 1990.
      [B4799, Hafn]

   $ ASCII
      (N) See: American Standard Code for Information Interchange.

   $ ASN.1
      (N) See: Abstract Syntax Notation One.

   $ asset
      (I) A system resource that is (a) required to be protected by an
      information system's security policy, (b) intended to be protected
      by a countermeasure, or (c) required for a system's mission.

   $ association
      (I) A cooperative relationship between system entities, usually
      for the purpose of transferring information between them. (See:
      security association.)

   $ assurance See: security assurance.

   $ assurance level
      (N) A rank on a hierarchical scale that judges the confidence
      someone can have that a TOE adequately fulfills stated security
      requirements. (See: assurance, certificate policy, EAL, TCSEC.)

      Example: U.S. Government guidance [M0404] describes four assurance
      levels for identity authentication, where each level "describes
      the [U.S. Federal Government] agency's degree of certainty that
      the user has presented [a credential] that refers to [the user's]
      identity." In that guidance, assurance is defined as (a) "the
      degree of confidence in the vetting process used to establish the
      identity of the individual to whom the credential was issued" and
      (b) "the degree of confidence that the individual who uses the
      credential is the individual to whom the credential was issued."

      The four levels are described as follows:
      -  Level 1: Little or no confidence in the asserted identity.
      -  Level 2: Some confidence in the asserted identity.
      -  Level 3: High confidence in the asserted identity.
      -  Level 4: Very high confidence in the asserted identity.

      Standards for determining these levels are provided in a NIST
      publication [SP12]. However, as noted there, an assurance level is
      "a degree of confidence, not a true measure of how secure the
      system actually is. This distinction is necessary because it is
      extremely difficult -- and in many cases, virtually impossible --
      to know exactly how secure a system is."

   $ asymmetric cryptography
      (I) A modern branch of cryptography (popularly known as "public-
      key cryptography") in which the algorithms use a pair of keys (a
      public key and a private key) and use a different component of the
      pair for each of two counterpart cryptographic operations (e.g.,

      encryption and decryption, or signature creation and signature
      verification). (See: key pair, symmetric cryptography.)

      Tutorial: Asymmetric algorithms have key management advantages
      over equivalently strong symmetric ones. First, one key of the
      pair need not be known by anyone but its owner; so it can more
      easily be kept secret. Second, although the other key is shared by
      all entities that use the algorithm, that key need not be kept
      secret from other, non-using entities; thus, the key-distribution
      part of key management can be done more easily.

      Asymmetric cryptography can be used to create algorithms for
      encryption, digital signature, and key agreement:
      -  In an asymmetric encryption algorithm (e.g., "RSA"), when Alice
         wants to ensure confidentiality for data she sends to Bob, she
         encrypts the data with a public key provided by Bob. Only Bob
         has the matching private key that is needed to decrypt the
         data. (Compare: seal.)
      -  In an asymmetric digital signature algorithm (e.g., "DSA"),
         when Alice wants to ensure data integrity or provide
         authentication for data she sends to Bob, she uses her private
         key to sign the data (i.e., create a digital signature based on
         the data). To verify the signature, Bob uses the matching
         public key that Alice has provided.
      -  In an asymmetric key-agreement algorithm (e.g., "Diffie-
         Hellman-Merkle"), Alice and Bob each send their own public key
         to the other party. Then each uses their own private key and
         the other's public key to compute the new key value.

   $ asymmetric key
      (I) A cryptographic key that is used in an asymmetric
      cryptographic algorithm. (See: asymmetric cryptography, private
      key, public key.)

   $ ATIS
      (N) See: "Alliance for Telecommunications Industry Solutions"
      under "ANSI".

   $ attack
      1. (I) An intentional act by which an entity attempts to evade
      security services and violate the security policy of a system.
      That is, an actual assault on system security that derives from an
      intelligent threat. (See: penetration, violation, vulnerability.)

      2. (I) A method or technique used in an assault (e.g.,
      masquerade). (See: blind attack, distributed attack.)

      Tutorial: Attacks can be characterized according to intent:
      -  An "active attack" attempts to alter system resources or affect
         their operation.
      -  A "passive attack" attempts to learn or make use of information
         from a system but does not affect system resources of that
         system. (See: wiretapping.)

      The object of a passive attack might be to obtain data that is
      needed for an off-line attack.
      -  An "off-line attack" is one in which the attacker obtains data
         from the target system and then analyzes the data on a
         different system of the attacker's own choosing, possibly in
         preparation for a second stage of attack on the target.

      Attacks can be characterized according to point of initiation:
      -  An "inside attack" is one that is initiated by an entity inside
         the security perimeter (an "insider"), i.e., an entity that is
         authorized to access system resources but uses them in a way
         not approved by the party that granted the authorization.
      -  An "outside attack" is initiated from outside the security
         perimeter, by an unauthorized or illegitimate user of the
         system (an "outsider"). In the Internet, potential outside
         attackers range from amateur pranksters to organized criminals,
         international terrorists, and hostile governments.
      Attacks can be characterized according to method of delivery:
      -  In a "direct attack", the attacker addresses attacking packets
         to the intended victim(s).
      -  In an "indirect attack", the attacker addresses packets to a
         third party, and the packets either have the address(es) of the
         intended victim(s) as their source address(es) or indicate the
         intended victim(s) in some other way. The third party responds
         by sending one or more attacking packets to the intended
         victims. The attacker can use third parties as attack
         amplifiers by providing a broadcast address as the victim
         address (e.g., "smurf attack"). (See: reflector attack.
         Compare: reflection attack, replay attack.)

      The term "attack" relates to some other basic security terms as
      shown in the following diagram:

      + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+
      | An Attack:              |  |Counter- |  | A System Resource:   |
      | i.e., A Threat Action   |  | measure |  | Target of the Attack |
      | +----------+            |  |         |  | +-----------------+  |
      | | Attacker |<==================||<=========                 |  |
      | |   i.e.,  |   Passive  |  |         |  | |  Vulnerability  |  |
      | | A Threat |<=================>||<========>                 |  |
      | |  Agent   |  or Active |  |         |  | +-------|||-------+  |
      | +----------+   Attack   |  |         |  |         VVV          |
      |                         |  |         |  | Threat Consequences  |
      + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+

   $ attack potential
      (I) The perceived likelihood of success should an attack be
      launched, expressed in terms of the attacker's ability (i.e.,
      expertise and resources) and motivation. (Compare: threat, risk.)

   $ attack sensing, warning, and response
      (I) A set of security services that cooperate with audit service
      to detect and react to indications of threat actions, including
      both inside and outside attacks. (See: indicator.)

   $ attack tree
      (I) A branching, hierarchical data structure that represents a set
      of potential approaches to achieving an event in which system
      security is penetrated or compromised in a specified way. [Moor]

      Tutorial: Attack trees are special cases of fault trees. The
      security incident that is the goal of the attack is represented as
      the root node of the tree, and the ways that an attacker could
      reach that goal are iteratively and incrementally represented as
      branches and subnodes of the tree. Each subnode defines a subgoal,
      and each subgoal may have its own set of further subgoals, etc.
      The final nodes on the paths outward from the root, i.e., the leaf
      nodes, represent different ways to initiate an attack. Each node
      other than a leaf is either an AND-node or an OR-node. To achieve
      the goal represented by an AND-node, the subgoals represented by
      all of that node's subnodes must be achieved; and for an OR-node,
      at least one of the subgoals must be achieved. Branches can be
      labeled with values representing difficulty, cost, or other attack
      attributes, so that alternative attacks can be compared.

   $ attribute
      (N) Information of a particular type concerning an identifiable
      system entity or object. An "attribute type" is the component of
      an attribute that indicates the class of information given by the
      attribute; and an "attribute value" is a particular instance of
      the class of information indicated by an attribute type. (See:
      attribute certificate.)

   $ attribute authority (AA)
      1. (N) A CA that issues attribute certificates.

      2. (O) "An authority [that] assigns privileges by issuing
      attribute certificates." [X509]

      Deprecated Usage: The abbreviation "AA" SHOULD NOT be used in an
      IDOC unless it is first defined in the IDOC.

   $ attribute certificate
      1. (I) A digital certificate that binds a set of descriptive data
      items, other than a public key, either directly to a subject name
      or to the identifier of another certificate that is a public-key
      certificate. (See: capability token.)

      2. (O) "A data structure, digitally signed by an [a]ttribute
      [a]uthority, that binds some attribute values with identification
      information about its holder." [X509]

      Tutorial: A public-key certificate binds a subject name to a
      public key value, along with information needed to perform certain
      cryptographic functions using that key. Other attributes of a
      subject, such as a security clearance, may be certified in a
      separate kind of digital certificate, called an attribute
      certificate. A subject may have multiple attribute certificates
      associated with its name or with each of its public-key
      certificates.

      An attribute certificate might be issued to a subject in the
      following situations:
      -  Different lifetimes: When the lifetime of an attribute binding
         is shorter than that of the related public-key certificate, or
         when it is desirable not to need to revoke a subject's public
         key just to revoke an attribute.
      -  Different authorities: When the authority responsible for the
         attributes is different than the one that issues the public-key
         certificate for the subject. (There is no requirement that an
         attribute certificate be issued by the same CA that issued the
         associated public-key certificate.)

   $ audit
      See: security audit.

   $ audit log
      (I) Synonym for "security audit trail".

   $ audit service
      (I) A security service that records information needed to
      establish accountability for system events and for the actions of
      system entities that cause them. (See: security audit.)

   $ audit trail
      (I) See: security audit trail.

   $ AUTH
      (I) See: POP3 AUTH.

   $ authenticate
      (I) Verify (i.e., establish the truth of) an attribute value
      claimed by or for a system entity or system resource. (See:
      authentication, validate vs. verify, "relationship between data
      integrity service and authentication services" under "data
      integrity service".)

      Deprecated Usage: In general English usage, this term is used with
      the meaning "to prove genuine" (e.g., an art expert authenticates
      a Michelangelo painting); but IDOCs should restrict usage as
      follows:
      -  IDOCs SHOULD NOT use this term to refer to proving or checking
         that data has not been changed, destroyed, or lost in an
         unauthorized or accidental manner. Instead, use "verify".
      -  IDOCs SHOULD NOT use this term to refer to proving the truth or
         accuracy of a fact or value such as a digital signature.
         Instead, use "verify".
      -  IDOCs SHOULD NOT use this term to refer to establishing the
         soundness or correctness of a construct, such as a digital
         certificate. Instead, use "validate".

   $ authentication
      (I) The process of verifying a claim that a system entity or
      system resource has a certain attribute value. (See: attribute,
      authenticate, authentication exchange, authentication information,
      credential, data origin authentication, peer entity
      authentication, "relationship between data integrity service and
      authentication services" under "data integrity service", simple
      authentication, strong authentication, verification, X.509.)

      Tutorial: Security services frequently depend on authentication of
      the identity of users, but authentication may involve any type of
      attribute that is recognized by a system. A claim may be made by a
      subject about itself (e.g., at login, a user typically asserts its
      identity) or a claim may be made on behalf of a subject or object
      by some other system entity (e.g., a user may claim that a data
      object originates from a specific source, or that a data object is
      classified at a specific security level).

      An authentication process consists of two basic steps:
      -  Identification step: Presenting the claimed attribute value
         (e.g., a user identifier) to the authentication subsystem.
      -  Verification step: Presenting or generating authentication
         information (e.g., a value signed with a private key) that acts
         as evidence to prove the binding between the attribute and that
         for which it is claimed. (See: verification.)

   $ authentication code
      (D) Synonym for a checksum based on cryptography. (Compare: Data
      Authentication Code, Message Authentication Code.)

      Deprecated Term: IDOCs SHOULD NOT use this uncapitalized term as a
      synonym for any kind of checksum, regardless of whether or not the
      checksum is cryptographic. Instead, use "checksum", "Data
      Authentication Code", "error detection code", "hash", "keyed
      hash", "Message Authentication Code", "protected checksum", or
      some other recommended term, depending on what is meant.

      The term mixes concepts in a potentially misleading way. The word
      "authentication" is misleading because the checksum may be used to
      perform a data integrity function rather than a data origin
      authentication function.

   $ authentication exchange
      1. (I) A mechanism to verify the identity of an entity by means of
      information exchange.

      2. (O) "A mechanism intended to ensure the identity of an entity
      by means of information exchange." [I7498-2]

   $ Authentication Header (AH)
      (I) An Internet protocol [R2402, R4302] designed to provide
      connectionless data integrity service and connectionless data
      origin authentication service for IP datagrams, and (optionally)
      to provide partial sequence integrity and protection against
      replay attacks. (See: IPsec. Compare: ESP.)

      Tutorial: Replay protection may be selected by the receiver when a
      security association is established. AH authenticates the upper-
      layer PDU that is carried as an IP SDU, and also authenticates as
      much of the IP PCI (i.e., the IP header) as possible. However,
      some IP header fields may change in transit, and the value of
      these fields, when the packet arrives at the receiver, may not be
      predictable by the sender. Thus, the values of such fields cannot
      be protected end-to-end by AH; protection of the IP header by AH
      is only partial when such fields are present.

      AH may be used alone, or in combination with the ESP, or in a
      nested fashion with tunneling. Security services can be provided
      between a pair of communicating hosts, between a pair of
      communicating security gateways, or between a host and a gateway.
      ESP can provide nearly the same security services as AH, and ESP
      can also provide data confidentiality service. The main difference
      between authentication services provided by ESP and AH is the
      extent of the coverage; ESP does not protect IP header fields
      unless they are encapsulated by AH.

   $ authentication information
      (I) Information used to verify an identity claimed by or for an
      entity. (See: authentication, credential, user. Compare:
      identification information.)

      Tutorial: Authentication information may exist as, or be derived
      from, one of the following: (a) Something the entity knows (see:
      password); (b) something the entity possesses (see: token); (c)
      something the entity is (see: biometric authentication).

   $ authentication service
      (I) A security service that verifies an identity claimed by or for
      an entity. (See: authentication.)

      Tutorial: In a network, there are two general forms of
      authentication service: data origin authentication service and
      peer entity authentication service.

   $ authenticity
      (I) The property of being genuine and able to be verified and be
      trusted. (See: authenticate, authentication, validate vs. verify.)

   $ authority
      (D) /PKI/ "An entity [that is] responsible for the issuance of
      certificates." [X509]

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      attribute authority, certification authority, registration
      authority, or similar terms; the shortened form may cause
      confusion. Instead, use the full term at the first instance of
      usage and then, if it is necessary to shorten text, use AA, CA,
      RA, and other abbreviations defined in this Glossary.

   $ authority certificate
      (D) "A certificate issued to an authority (e.g. either to a
      certification authority or to an attribute authority)." [X509]
      (See: authority.)

      Deprecated Term: IDOCs SHOULD NOT use this term because it is
      ambiguous. Instead, use the full term "certification authority
      certificate", "attribute authority certificate", "registration
      authority certificate", etc. at the first instance of usage and
      then, if it is necessary to shorten text, use AA, CA, RA, and
      other abbreviations defined in this Glossary.

   $ Authority Information Access extension
      (I) The private extension defined by PKIX for X.509 certificates
      to indicate "how to access CA information and services for the
      issuer of the certificate in which the extension appears.
      Information and services may include on-line validation services
      and CA policy data." [R3280] (See: private extension.)

   $ authorization
      1a. (I) An approval that is granted to a system entity to access a
      system resource. (Compare: permission, privilege.)

      Usage: Some synonyms are "permission" and "privilege". Specific
      terms are preferred in certain contexts:
      -  /PKI/ "Authorization" SHOULD be used, to align with
         "certification authority" in the standard [X509].
      -  /role-based access control/ "Permission" SHOULD be used, to
         align with the standard [ANSI].
      -  /computer operating systems/ "Privilege" SHOULD be used, to
         align with the literature. (See: privileged process, privileged
         user.)

      Tutorial: The semantics and granularity of authorizations depend
      on the application and implementation (see: "first law" under
      "Courtney's laws"). An authorization may specify a particular
      access mode -- such as read, write, or execute -- for one or more
      system resources.

      1b. (I) A process for granting approval to a system entity to
      access a system resource.

      2. (O) /SET/ "The process by which a properly appointed person or
      persons grants permission to perform some action on behalf of an
      organization. This process assesses transaction risk, confirms
      that a given transaction does not raise the account holder's debt
      above the account's credit limit, and reserves the specified
      amount of credit. (When a merchant obtains authorization, payment
      for the authorized amount is guaranteed -- provided, of course,
      that the merchant followed the rules associated with the
      authorization process.)" [SET2]

   $ authorization credential
      (I) See: /access control/ under "credential".

   $ authorize
      (I) Grant an authorization to a system entity.

   $ authorized user
      (I) /access control/ A system entity that accesses a system
      resource for which the entity has received an authorization.
      (Compare: insider, outsider, unauthorized user.)

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the term is used in many ways and could
      easily be misunderstood.

   $ automated information system
      See: information system.

   $ availability
      1. (I) The property of a system or a system resource being
      accessible, or usable or operational upon demand, by an authorized
      system entity, according to performance specifications for the
      system; i.e., a system is available if it provides services
      according to the system design whenever users request them. (See:
      critical, denial of service. Compare: precedence, reliability,
      survivability.)

      2. (O) "The property of being accessible and usable upon demand by
      an authorized entity." [I7498-2]

      3. (D) "Timely, reliable access to data and information services
      for authorized users." [C4009]

      Deprecated Definition: IDOCs SHOULD NOT use the term with
      definition 3; the definition mixes "availability" with
      "reliability", which is a different property. (See: reliability.)

      Tutorial: Availability requirements can be specified by
      quantitative metrics, but sometimes are stated qualitatively, such
      as in the following:
      -  "Flexible tolerance for delay" may mean that brief system
         outages do not endanger mission accomplishment, but extended
         outages may endanger the mission.
      -  "Minimum tolerance for delay" may mean that mission
         accomplishment requires the system to provide requested
         services in a short time.

   $ availability service
      (I) A security service that protects a system to ensure its
      availability.

      Tutorial: This service addresses the security concerns raised by
      denial-of-service attacks. It depends on proper management and
      control of system resources, and thus depends on access control
      service and other security services.

   $ avoidance
      (I) See: secondary definition under "security".

   $ B1, B2, or B3 computer system
      (O) /TCSEC/ See: Tutorial under "Trusted Computer System
      Evaluation Criteria".

   $ back door
      1. (I) /COMPUSEC/ A computer system feature -- which may be (a) an
      unintentional flaw, (b) a mechanism deliberately installed by the
      system's creator, or (c) a mechanism surreptitiously installed by
      an intruder -- that provides access to a system resource by other
      than the usual procedure and usually is hidden or otherwise not
      well-known. (See: maintenance hook. Compare: Trojan Horse.)

      Example: A way to access a computer other than through a normal
      login. Such an access path is not necessarily designed with
      malicious intent; operating systems sometimes are shipped by the
      manufacturer with hidden accounts intended for use by field
      service technicians or the vendor's maintenance programmers.

      2. (I) /cryptography/ A feature of a cryptographic system that
      makes it easily possible to break or circumvent the protection
      that the system is designed to provide.

      Example: A feature that makes it possible to decrypt cipher text
      much more quickly than by brute-force cryptanalysis, without
      having prior knowledge of the decryption key.

   $ back up
      (I) /verb/ Create a reserve copy of data or, more generally,
      provide alternate means to perform system functions despite loss
      of system resources. (See: contingency plan. Compare: archive.)

   $ backup
      (I) /noun or adjective/ Refers to alternate means of performing
      system functions despite loss of system resources. (See:
      contingency plan).

      Example: A reserve copy of data, preferably one that is stored
      separately from the original, for use if the original becomes lost
      or damaged. (Compare: archive.)

   $ bagbiter
      (D) /slang/ "An entity, such as a program or a computer, that
      fails to work or that works in a remarkably clumsy manner. A
      person who has caused some trouble, inadvertently or otherwise,
      typically by failing to program the computer properly." [NCSSG]
      (See: flaw.)

      Deprecated Term: It is likely that other cultures use different
      metaphors for these concepts. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ baggage
      (O) /SET/ An "opaque encrypted tuple, which is included in a SET
      message but appended as external data to the PKCS encapsulated
      data. This avoids superencryption of the previously encrypted
      tuple, but guarantees linkage with the PKCS portion of the
      message." [SET2]

      Deprecated Usage: IDOCs SHOULD NOT use this term to describe a
      data element, except in the form "SET(trademark) baggage" with the
      meaning given above.

   $ baked-in security
      (D) The inclusion of security mechanisms in an information system
      beginning at an early point in the system's lifecycle, i.e.,
      during the design phase, or at least early in the implementation
      phase. (Compare: add-on security.)

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term (unless they also
      provide a definition like this one). (See: Deprecated Usage under
      "Green Book".)

   $ bandwidth
      (I) The total width of the frequency band that is available to or
      used by a communication channel; usually expressed in Hertz (Hz).
      (RFC 3753) (Compare: channel capacity.)

   $ bank identification number (BIN)
      1. (O) The digits of a credit card number that identify the
      issuing bank. (See: primary account number.)

      2. (O) /SET/ The first six digits of a primary account number.

   $ Basic Encoding Rules (BER)
      (I) A standard for representing ASN.1 data types as strings of
      octets. [X690] (See: Distinguished Encoding Rules.)

      Deprecated Usage: Sometimes incorrectly treated as part of ASN.1.
      However, ASN.1 properly refers only to a syntax description
      language, and not to the encoding rules for the language.

   $ Basic Security Option
      (I) See: secondary definition under "IPSO".

   $ bastion host
      (I) A strongly protected computer that is in a network protected
      by a firewall (or is part of a firewall) and is the only host (or
      one of only a few) in the network that can be directly accessed
      from networks on the other side of the firewall. (See: firewall.)

      Tutorial: Filtering routers in a firewall typically restrict
      traffic from the outside network to reaching just one host, the
      bastion host, which usually is part of the firewall. Since only
      this one host can be directly attacked, only this one host needs
      to be very strongly protected, so security can be maintained more
      easily and less expensively. However, to allow legitimate internal
      and external users to access application resources through the
      firewall, higher-layer protocols and services need to be relayed
      and forwarded by the bastion host. Some services (e.g., DNS and
      SMTP) have forwarding built in; other services (e.g., TELNET and
      FTP) require a proxy server on the bastion host.

   $ BBN Technologies Corp. (BBN)
      (O) The research-and-development company (originally called Bolt
      Baranek and Newman, Inc.) that built the ARPANET.

   $ BCA
      (O) See: brand certification authority.

   $ BCR
      (O) See: BLACK/Crypto/RED.

   $ BCI
      (O) See: brand CRL identifier.

   $ Bell-LaPadula model
      (N) A formal, mathematical, state-transition model of
      confidentiality policy for multilevel-secure computer systems
      [Bell]. (Compare: Biba model, Brewer-Nash model.)

      Tutorial: The model, devised by David Bell and Leonard LaPadula at
      The MITRE Corporation in 1973, characterizes computer system
      elements as subjects and objects. To determine whether or not a
      subject is authorized for a particular access mode on an object,
      the clearance of the subject is compared to the classification of
      the object. The model defines the notion of a "secure state", in
      which the only permitted access modes of subjects to objects are
      in accordance with a specified security policy. It is proven that
      each state transition preserves security by moving from secure
      state to secure state, thereby proving that the system is secure.
      In this model, a multilevel-secure system satisfies several rules,
      including the "confinement property" (a.k.a. the "*-property"),
      the "simple security property", and the "tranquility property".

   $ benign
      1. (N) /COMSEC/ "Condition of cryptographic data [such] that [the
      data] cannot be compromised by human access [to the data]."
      [C4009]

      2. (O) /COMPUSEC/ See: secondary definition under "trust".

   $ benign fill
      (N) Process by which keying material is generated, distributed,
      and placed into an ECU without exposure to any human or other
      system entity, except the cryptographic module that consumes and
      uses the material. (See: benign.)

   $ BER
      (I) See: Basic Encoding Rules.

   $ beyond A1
      1. (O) /formal/ A level of security assurance that is beyond the
      highest level (level A1) of criteria specified by the TCSEC. (See:
      Tutorial under "Trusted Computer System Evaluation Criteria".)

      2. (O) /informal/ A level of trust so high that it is beyond
      state-of-the-art technology; i.e., it cannot be provided or
      verified by currently available assurance methods, and especially
      not by currently available formal methods.

   $ Biba integrity
      (N) Synonym for "source integrity".

   $ Biba model
      (N) A formal, mathematical, state-transition model of integrity
      policy for multilevel-secure computer systems [Biba]. (See: source
      integrity. Compare: Bell-LaPadula model.)

      Tutorial: This model for integrity control is analogous to the
      Bell-LaPadula model for confidentiality control. Each subject and
      object is assigned an integrity level and, to determine whether or
      not a subject is authorized for a particular access mode on an
      object, the integrity level of the subject is compared to that of
      the object. The model prohibits the changing of information in an
      object by a subject with a lesser or incomparable level. The rules
      of the Biba model are duals of the corresponding rules in the
      Bell-LaPadula model.

   $ billet
      (N) "A personnel position or assignment that may be filled by one
      person." [JCP1] (Compare: principal, role, user.)

      Tutorial: In an organization, a "billet" is a populational
      position, of which there is exactly one instance; but a "role" is
      functional position, of which there can be multiple instances.
      System entities are in one-to-one relationships with their
      billets, but may be in many-to-one and one-to-many relationships
      with their roles.

   $ BIN
      (O) See: bank identification number.

   $ bind
      (I) To inseparably associate by applying some security mechanism.

      Example: A CA creates a public-key certificate by using a digital
      signature to bind together (a) a subject name, (b) a public key,
      and usually (c) some additional data items (e.g., "X.509 public-
      key certificate").

   $ biometric authentication
      (I) A method of generating authentication information for a person
      by digitizing measurements of a physical or behavioral

      characteristic, such as a fingerprint, hand shape, retina pattern,
      voiceprint, handwriting style, or face.

   $ birthday attack
      (I) A class of attacks against cryptographic functions, including
      both encryption functions and hash functions. The attacks take
      advantage of a statistical property: Given a cryptographic
      function having an N-bit output, the probability is greater than
      1/2 that for 2**(N/2) randomly chosen inputs, the function will
      produce at least two outputs that are identical. (See: Tutorial
      under "hash function".)

      Derivation: From the somewhat surprising fact (often called the
      "birthday paradox") that although there are 365 days in a year,
      the probability is greater than 1/2 that two of more people share
      the same birthday in any randomly chosen group of 23 people.

      Birthday attacks enable an adversary to find two inputs for which
      a cryptographic function produces the same cipher text (or find
      two inputs for which a hash functions produces the same hash
      result) much faster than a brute-force attack can; and a clever
      adversary can use such a capability to create considerable
      mischief. However, no birthday attack can enable an adversary to
      decrypt a given cipher text (or find a hash input that results in
      a given hash result) any faster than a brute-force attack can.

   $ bit
      (I) A contraction of the term "binary digit"; the smallest unit of
      information storage, which has two possible states or values. The
      values usually are represented by the symbols "0" (zero) and "1"
      (one). (See: block, byte, nibble, word.)

   $ bit string
      (I) A sequence of bits, each of which is either "0" or "1".

   $ BLACK
      1. (N) Designation for data that consists only of cipher text, and
      for information system equipment items or facilities that handle
      only cipher text. Example: "BLACK key". (See: BCR, color change,
      RED/BLACK separation. Compare: RED.)

      2. (O) /U.S. Government/ "Designation applied to information
      systems, and to associated areas, circuits, components, and
      equipment, in which national security information is encrypted or
      is not processed." [C4009]

      3. (D) Any data that can be disclosed without harm.

      Deprecated Definition: IDOCs SHOULD NOT use the term with
      definition 3 because the definition is ambiguous with regard to
      whether or not the data is protected.

   $ BLACK/Crypto/RED (BCR)
      (N) An experimental, end-to-end, network packet encryption system
      developed in a working prototype form by BBN and the Collins Radio
      division of Rockwell Corporation in the 1975-1980 time frame for
      the U.S. DoD. BCR was the first network security system to support
      TCP/IP traffic, and it incorporated the first DES chips that were
      validated by the U.S. National Bureau of Standards (now called
      NIST). BCR also was the first to use a KDC and an ACC to manage
      connections.

   $ BLACK key
      (N) A key that is protected with a key-encrypting key and that
      must be decrypted before use. (See: BLACK. Compare: RED key.)

   $ BLACKER
      (O) An end-to-end encryption system for computer data networks
      that was developed by the U.S. DoD in the 1980s to provide host-
      to-host data confidentiality service for datagrams at OSIRM Layer
      3. [Weis] (Compare: CANEWARE, IPsec.)

      Tutorial: Each user host connects to its own bump-in-the-wire
      encryption device called a BLACKER Front End (BFE, TSEC/KI-111),
      through which the host connects to the subnetwork. The system also
      includes two types of centralized devices: one or more KDCs
      connect to the subnetwork and communicate with assigned sets of
      BFEs, and one or more ACCs connect to the subnetwork and
      communicate with assigned KDCs. BLACKER uses only symmetric
      encryption. A KDC distributes session keys to BFE pairs as
      authorized by an ACC. Each ACC maintains a database for a set of
      BFEs, and the database determines which pairs from that set (i.e.,
      which pairs of user hosts behind the BFEs) are authorized to
      communicate and at what security levels.

      The BLACKER system is MLS in three ways: (a) The BFEs form a
      security perimeter around a subnetwork, separating user hosts from
      the subnetwork, so that the subnetwork can operate at a different
      security level (possibly a lower, less expensive level) than the
      hosts. (b) The BLACKER components are trusted to separate
      datagrams of different security levels, so that each datagram of a
      given security level can be received only by a host that is
      authorized for that security level; and thus BLACKER can separate
      host communities that operate at different security levels. (c)
      The host side of a BFE is itself MLS and can recognize a security
      label on each packet, so that an MLS user host can be authorized

      to successively transmit datagrams that are labeled with different
      security levels.

   $ blind attack
      (I) A type of network-based attack method that does not require
      the attacking entity to receive data traffic from the attacked
      entity; i.e., the attacker does not need to "see" data packets
      sent by the victim. Example: SYN flood.

      Tutorial: If an attack method is blind, the attacker's packets can
      carry (a) a false IP source address (making it difficult for the
      victim to find the attacker) and (b) a different address on every
      packet (making it difficult for the victim to block the attack).
      If the attacker needs to receive traffic from the victim, the
      attacker must either (c) reveal its own IP address to the victim
      (which enables the victim to find the attacker or block the attack
      by filtering) or (d) provide a false address and also subvert
      network routing mechanisms to divert the returning packets to the
      attacker (which makes the attack more complex, more difficult, or
      more expensive). [R3552]

   $ block
      (I) A bit string or bit vector of finite length. (See: bit, block
      cipher. Compare: byte, word.)

      Usage: An "N-bit block" contains N bits, which usually are
      numbered from left to right as 1, 2, 3, ..., N.

   $ block cipher
      (I) An encryption algorithm that breaks plain text into fixed-size
      segments and uses the same key to transform each plaintext segment
      into a fixed-size segment of cipher text. Examples: AES, Blowfish,
      DEA, IDEA, RC2, and SKIPJACK. (See: block, mode. Compare: stream
      cipher.)

      Tutorial: A block cipher can be adapted to have a different
      external interface, such as that of a stream cipher, by using a
      mode of cryptographic operation to package the basic algorithm.
      (See: CBC, CCM, CFB, CMAC, CTR, DEA, ECB, OFB.)

   $ Blowfish
      (N) A symmetric block cipher with variable-length key (32 to 448
      bits) designed in 1993 by Bruce Schneier as an unpatented,
      license-free, royalty-free replacement for DES or IDEA. [Schn]
      (See: Twofish.)

   $ brain-damaged
      (D) /slang/ "Obviously wrong: extremely poorly designed. Calling
      something brain-damaged is very extreme. The word implies that the
      thing is completely unusable, and that its failure to work is due
      to poor design, not accident." [NCSSG] (See: flaw.)

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ brand
      1. (I) A distinctive mark or name that identifies a product or
      business entity.

      2. (O) /SET/ The name of a payment card. (See: BCA.)

      Tutorial: Financial institutions and other companies have founded
      payment card brands, protect and advertise the brands, establish
      and enforce rules for use and acceptance of their payment cards,
      and provide networks to interconnect the financial institutions.
      These brands combine the roles of issuer and acquirer in
      interactions with cardholders and merchants. [SET1]

   $ brand certification authority (BCA)
      (O) /SET/ A CA owned by a payment card brand, such as MasterCard,
      Visa, or American Express. [SET2] (See: certification hierarchy,
      SET.)

   $ brand CRL identifier (BCI)
      (O) /SET/ A digitally signed list, issued by a BCA, of the names
      of CAs for which CRLs need to be processed when verifying
      signatures in SET messages. [SET2]

   $ break
      (I) /cryptography/ To successfully perform cryptanalysis and thus
      succeed in decrypting data or performing some other cryptographic
      function, without initially having knowledge of the key that the
      function requires. (See: penetrate, strength, work factor.)

      Usage: This term applies to encrypted data or, more generally, to
      a cryptographic algorithm or cryptographic system. Also, while the
      most common use is to refer to completely breaking an algorithm,
      the term is also used when a method is found that substantially
      reduces the work factor.

   $ Brewer-Nash model
      (N) A security model [BN89] to enforce the Chinese wall policy.
      (Compare: Bell-LaPadula model, Clark-Wilson model.)

      Tutorial: All proprietary information in the set of commercial
      firms F(1), F(2), ..., F(N) is categorized into mutually exclusive
      conflict-of-interest classes I(1), I(2), ..., I(M) that apply
      across all firms. Each firm belongs to exactly one class. The
      Brewer-Nash model has the following mandatory rules:
      -  Brewer-Nash Read Rule: Subject S can read information object O
         from firm F(i) only if either (a) O is from the same firm as
         some object previously read by S *or* (b) O belongs to a class
         I(i) from which S has not previously read any object. (See:
         object, subject.)
      -  Brewer-Nash Write Rule: Subject S can write information object
         O to firm F(i) only if (a) S can read O by the Brewer-Nash Read
         Rule *and* (b) no object can be read by S from a different firm
         F(j), no matter whether F(j) belongs to the same class as F(i)
         or to a different class.

   $ bridge
      (I) A gateway for traffic flowing at OSIRM Layer 2 between two
      networks (usually two LANs). (Compare: bridge CA, router.)

   $ bridge CA
      (I) A PKI consisting of only a CA that cross-certifies with CAs of
      some other PKIs. (See: cross-certification. Compare: bridge.)

      Tutorial: A bridge CA functions as a hub that enables a
      certificate user in any of the PKIs that attach to the bridge, to
      validate certificates issued in the other attached PKIs.

      For example, a bridge CA (BCA)                 CA1
      could cross-certify with four                   ^
      PKIs that have the roots CA1,                   |
      CA2, CA3, and CA4. The cross-                   v
      certificates that the roots            CA2 <-> BCA <-> CA3
      exchange with the BCA enable an                 ^
      end entity EE1 certified under                  |
      under CA1 in PK1 to construct                   v
      a certification path needed to                 CA4
      validate the certificate of
      end entity EE2 under CA2,           CA1 -> BCA -> CA2 -> EE2
      or vice versa.                     CA2 -> BCA -> CA1 -> EE1

   $ British Standard 7799
      (N) Part 1 of the standard is a code of practice for how to secure
      an information system. Part 2 specifies the management framework,
      objectives, and control requirements for information security
      management systems. [BS7799] (See: ISO 17799.)

   $ browser
      (I) A client computer program that can retrieve and display
      information from servers on the World Wide Web. Examples: Netscape
      Navigator and Microsoft Internet Explorer.

   $ brute force
      (I) A cryptanalysis technique or other kind of attack method
      involving an exhaustive procedure that tries a large number of
      possible solutions to the problem. (See: impossible, strength,
      work factor.)

      Tutorial: In some cases, brute force involves trying all of the
      possibilities. For example, for cipher text where the analyst
      already knows the decryption algorithm, a brute-force technique
      for finding matching plain text is to decrypt the message with
      every possible key. In other cases, brute force involves trying a
      large number of possibilities but substantially fewer than all of
      them. For example, given a hash function that produces an N-bit
      hash result, the probability is greater than 1/2 that the analyst
      will find two inputs that have the same hash result after trying
      only 2**(N/2) randomly chosen inputs. (See: birthday attack.)

   $ BS7799
      (N) See: British Standard 7799.

   $ buffer overflow
      (I) Any attack technique that exploits a vulnerability resulting
      from computer software or hardware that does not check for
      exceeding the bounds of a storage area when data is written into a
      sequence of storage locations beginning in that area.

      Tutorial: By causing a normal system operation to write data
      beyond the bounds of a storage area, the attacker seeks to either
      disrupt system operation or cause the system to execute malicious
      software inserted by the attacker.

   $ buffer zone
      (I) A neutral internetwork segment used to connect other segments
      that each operate under a different security policy.

      Tutorial: To connect a private network to the Internet or some
      other relatively public network, one could construct a small,
      separate, isolated LAN and connect it to both the private network
      and the public network; one or both of the connections would
      implement a firewall to limit the traffic that could pass through
      the buffer zone.

   $ bulk encryption
      1. (I) Encryption of multiple channels by aggregating them into a
      single transfer path and then encrypting that path. (See:
      channel.)

      2. (O) "Simultaneous encryption of all channels of a multichannel
      telecommunications link." [C4009] (Compare: bulk keying material.)

      Usage: The use of "simultaneous" in definition 2 could be
      interpreted to mean that multiple channels are encrypted
      separately but at the same time. However, the common meaning of
      the term is that multiple data flows are combined into a single
      stream and then that stream is encrypted as a whole.

   $ bulk key
      (D) In a few published descriptions of hybrid encryption for SSH,
      Windows 2000, and other applications, this term refers to a
      symmetric key that (a) is used to encrypt a relatively large
      amount of data and (b) is itself encrypted with a public key.
      (Compare: bulk keying material, session key.)

      Example: To send a large file to Bob, Alice (a) generates a
      symmetric key and uses it to encrypt the file (i.e., encrypt the
      bulk of the information that is to be sent) and then (b) encrypts
      that symmetric key (the "bulk key") with Bob's public key.

      Deprecated Term: IDOCs SHOULD NOT use this term or definition; the
      term is not well-established and could be confused with the
      established term "bulk keying material". Instead, use "symmetric
      key" and carefully explain how the key is applied.

   $ bulk keying material
      (N) Refers to handling keying material in large quantities, e.g.,
      as a dataset that contains many items of keying material. (See:
      type 0. Compare: bulk key, bulk encryption.)

   $ bump-in-the-stack
      (I) An implementation approach that places a network security
      mechanism inside the system that is to be protected. (Compare:
      bump-in-the-wire.)

      Example: IPsec can be implemented inboard, in the protocol stack
      of an existing system or existing system design, by placing a new
      layer between the existing IP layer and the OSIRM Layer 3 drivers.
      Source code access for the existing stack is not required, but the
      system that contains the stack does need to be modified [R4301].

   $ bump-in-the-wire
      (I) An implementation approach that places a network security
      mechanism outside of the system that is to be protected. (Compare:
      bump-in-the-stack.)

      Example: IPsec can be implemented outboard, in a physically
      separate device, so that the system that receives the IPsec
      protection does not need to be modified at all [R4301]. Military-
      grade link encryption has mainly been implemented as bump-in-the-
      wire devices.

   $ business-case analysis
      (N) An extended form of cost-benefit analysis that considers
      factors beyond financial metrics, including security factors such
      as the requirement for security services, their technical and
      programmatic feasibility, their qualitative benefits, and
      associated risks. (See: risk analysis.)

   $ byte
      (I) A fundamental unit of computer storage; the smallest
      addressable unit in a computer's architecture. Usually holds one
      character of information and, today, usually means eight bits.
      (Compare: octet.)

      Usage: Understood to be larger than a "bit", but smaller than a
      "word". Although "byte" almost always means "octet" today, some
      computer architectures have had bytes in other sizes (e.g., six
      bits, nine bits). Therefore, an STD SHOULD state the number of
      bits in a byte where the term is first used in the STD.

   $ C field
      (D) See: Compartments field.

   $ C1 or C2 computer system
      (O) /TCSEC/ See: Tutorial under "Trusted Computer System
      Evaluation Criteria".

   $ CA
      (I) See: certification authority.

   $ CA certificate
      (D) "A [digital] certificate for one CA issued by another CA."
      [X509]

      Deprecated Definition: IDOCs SHOULD NOT use the term with this
      definition; the definition is ambiguous with regard to how the
      certificate is constructed and how it is intended to be used.
      IDOCs that use this term SHOULD provide a technical definition for
      it. (See: certificate profile.)

      Tutorial: There is no single, obvious choice for a technical
      definition of this term. Different PKIs can use different
      certificate profiles, and X.509 provides several choices of how to
      issue certificates to CAs. For example, one possible definition is
      the following: A v3 X.509 public-key certificate that has a
      "basicConstraints" extension containing a "cA" value of "TRUE".
      That would specifically indicate that "the certified public key
      may be used to verify certificate signatures", i.e., that the
      private key may be used by a CA.

      However, there also are other ways to indicate such usage. The
      certificate may have a "key Usage" extension that indicates the
      purposes for which the public key may be used, and one of the
      values that X.509 defines for that extension is "keyCertSign", to
      indicate that the certificate may be used for verifying a CA's
      signature on certificates. If "keyCertSign" is present in a
      certificate that also has a "basicConstraints" extension, then
      "cA" is set to "TRUE" in that extension. Alternatively, a CA could
      be issued a certificate in which "keyCertSign" is asserted without
      "basicConstraints" being present; and an entity that acts as a CA
      could be issued a certificate with "keyUsage" set to other values,
      either with or without "keyCertSign".

   $ CA domain
      (N) /PKI/ A security policy domain that "consists of a CA and its
      subjects [i.e., the entities named in the certificates issued by
      the CA]. Sometimes referred to as a PKI domain." [PAG] (See:
      domain.)

   $ Caesar cipher
      (I) A cipher that is defined for an alphabet of N characters,
      A(1), A(2), ..., A(N), and creates cipher text by replacing each
      plaintext character A(i) by A(i+K, mod N) for some 0<K<N+1. [Schn]

      Examples: (a) During the Gallic wars, Julius Caesar used a cipher
      with K=3. In a Caesar cipher with K=3 for the English alphabet, A
      is replaced by D, B by E, C by F, ..., W by Z, X by A, Y by B, Z

      by C. (b) UNIX systems sometimes include "ROT13" software that
      implements a Caesar cipher with K=13 (i.e., ROTate by 13).

   $ call back
      (I) An authentication technique for terminals that remotely access
      a computer via telephone lines; the host system disconnects the
      caller and then reconnects on a telephone number that was
      previously authorized for that terminal.

   $ CAM
      (O) See: Certificate Arbitrator Module.

   $ CANEWARE
      (O) An end-to-end encryption system for computer data networks
      that was developed by the U.S. DoD in the 1980s to provide host-
      to-host data confidentiality service for datagrams in OSIRM Layer
      3. [Roge] (Compare: BLACKER, IPsec.)

      Tutorial: Each user host connects to its own bump-in-the-wire
      encryption device called a CANEWARE Front End (CFE), through which
      the host connects to the subnetwork. CANEWARE uses symmetric
      encryption for CFE-to-CFE traffic, but also uses FIREFLY to
      establish those session keys. The public-key certificates issued
      by the FIREFLY system include credentials for mandatory access
      control. For discretionary access control, the system also
      includes one or more centralized CANEWARE Control Processors
      (CCPs) that connect to the subnetwork, maintain a database for
      discretionary access control authorizations, and communicate those
      authorizations to assigned sets of CFEs.

      The CANEWARE system is MLS in only two of the three ways that
      BLACKER is MLS: (a) Like BLACKER BFEs, CFEs form a security
      perimeter around a subnetwork, separating user hosts from the
      subnetwork, so that the subnetwork can operate at a different
      security level than the hosts. (b) Like BLACKER, the CANEWARE
      components are trusted to separate datagrams of different security
      levels, so that each datagram of a given security level can be
      received only by a host that is authorized for that security
      level; and thus CANEWARE can separate host communities that
      operate at different security levels. (c) Unlike a BFE, the host
      side of a CFE is not MLS, and treats all packets received from a
      user host as being at the same mandatory security level.

   $ capability list
      (I) /information system/ A mechanism that implements access
      control for a system entity by enumerating the system resources
      that the entity is permitted to access and, either implicitly or
      explicitly, the access modes granted for each resource. (Compare:

      access control list, access control matrix, access profile,
      capability token.)

   $ capability token
      (I) A token (usually an unforgeable data object) that gives the
      bearer or holder the right to access a system resource. Possession
      of the token is accepted by a system as proof that the holder has
      been authorized to access the resource indicated by the token.
      (See: attribute certificate, capability list, credential, digital
      certificate, ticket, token.)

   $ Capability Maturity Model (CMM)
      (N) Method for judging the maturity of software processes in an
      organization and for identifying crucial practices needed to
      increase process maturity. [Chris] (Compare: Common Criteria.)

      Tutorial: The CMM does not specify security evaluation criteria
      (see: assurance level), but its use may improve security
      assurance. The CMM describes principles and practices that can
      improve software processes in terms of evolving from ad hoc
      processes to disciplined processes. The CMM has five levels:
      -  Initial: Software processes are ad hoc or chaotic, and few are
         well-defined. Success depends on individual effort and heroics.
      -  Repeatable: Basic project management processes are established
         to track cost, schedule, and functionality. Necessary process
         discipline is in place to repeat earlier successes on projects
         with similar applications.
      -  Defined: Software process for both management and engineering
         activities is documented, standardized, and integrated into a
         standard software process for the organization. Each project
         uses an approved, tailored version of the organization's
         standard process for developing and maintaining software.
      -  Managed: Detailed measures of software process and product
         quality are collected. Both software process and products are
         quantitatively understood and controlled.
      -  Optimizing: Continuous process improvement is enabled by
         quantitative feedback from the process and from piloting
         innovative ideas and technologies.

   $ CAPI
      (I) See: cryptographic application programming interface.

   $ CAPSTONE
      (N) An integrated microcircuit (in MYK-8x series manufactured by
      Mykotronx, Inc.) that implements SKIPJACK, KEA, DSA, SHA, and
      basic mathematical functions needed to support asymmetric
      cryptography; has a non-deterministic random number generator; and
      supports key escrow. (See: FORTEZZA. Compare: CLIPPER.)

   $ card
      See: cryptographic card, FORTEZZA, payment card, PC card, smart
      card, token.

   $ card backup
      See: token backup.

   $ card copy
      See: token copy.

   $ card restore
      See: token restore.

   $ cardholder
      1. (I) An entity to whom or to which a card has been issued.

      Usage: Usually refers to a living human being, but might refer (a)
      to a position (see: billet, role) in an organization or (b) to an
      automated process. (Compare: user.)

      2. (O) /SET/ "The holder of a valid payment card account and user
      of software supporting electronic commerce." [SET2] A cardholder
      is issued a payment card by an issuer. SET ensures that in the
      cardholder's interactions with merchants, the payment card account
      information remains confidential. [SET1]

   $ cardholder certificate
      (O) /SET/ A digital certificate that is issued to a cardholder
      upon approval of the cardholder's issuing financial institution
      and that is transmitted to merchants with purchase requests and
      encrypted payment instructions, carrying assurance that the
      account number has been validated by the issuing financial
      institution and cannot be altered by a third party. [SET1]

   $ cardholder certification authority (CCA)
      (O) /SET/ A CA responsible for issuing digital certificates to
      cardholders and operated on behalf of a payment card brand, an
      issuer, or another party according to brand rules. A CCA maintains
      relationships with card issuers to allow for the verification of
      cardholder accounts. A CCA does not issue a CRL but does
      distribute CRLs issued by root CAs, brand CAs, geopolitical CAs,
      and payment gateway CAs. [SET2]

   $ CAST
      (N) A design procedure for symmetric encryption algorithms, and a
      resulting family of algorithms, invented by Carlisle Adams (C.A.)
      and Stafford Tavares (S.T.). [R2144, R2612]

   $ category
      (I) A grouping of sensitive information items to which a non-
      hierarchical restrictive security label is applied to increase
      protection of the data. (See: formal access approval. Compare:
      compartment, classification.)

   $ CAW
      (N) See: certification authority workstation.

   $ CBC
      (N) See: cipher block chaining.

   $ CCA
      (O) See: cardholder certification authority.

   $ CCEP
      (O) See: Commercial COMSEC Endorsement Program.

   $ CCI
      (O) See: Controlled Cryptographic Item.

   $ CCITT
      (N) Acronym for French translation of International Telephone and
      Telegraph Consultative Committee. Now renamed ITU-T.

   $ CCM
      (N) See: Counter with Cipher Block Chaining-Message Authentication
      Code.

   $ CERIAS
      (O) Purdue University's Center for Education and Research in
      Information Assurance and Security, which includes faculty from
      multiple schools and departments and takes a multidisciplinary
      approach to security problems ranging from technical to ethical,
      legal, educational, communicational, linguistic, and economic.

   $ CERT
      (I) See: computer emergency response team.

   $ certificate
      1. (I) /general English/ A document that attests to the truth of
      something or the ownership of something.

      2. (I) /general security/ See: capability token, digital
      certificate.

      3. (I) /PKI/ See: attribute certificate, public-key certificate.

   $ Certificate Arbitrator Module (CAM)
      (O) An open-source software module that is designed to be
      integrated with an application for routing, replying to, and
      otherwise managing and meditating certificate validation requests
      between that application and the CAs in the ACES PKI.

   $ certificate authority
      (D) Synonym for "certification authority".

      Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
      careless use of the term "certification authority", which is
      preferred in PKI standards (e.g., [X509, R3280]).

   $ certificate chain
      (D) Synonym for "certification path". (See: trust chain.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it duplicates the
      meaning of a standardized term. Instead, use "certification path".

   $ certificate chain validation
      (D) Synonym for "certificate validation" or "path validation".

      Deprecated Term: IDOCs SHOULD NOT use this term; it duplicates the
      meaning of standardized terms and mixes concepts in a potentially
      misleading way. Instead, use "certificate validation" or "path
      validation", depending on what is meant. (See: validate vs.
      verify.)

   $ certificate creation
      (I) The act or process by which a CA sets the values of a digital
      certificate's data fields and signs it. (See: issue.)

   $ certificate expiration
      (I) The event that occurs when a certificate ceases to be valid
      because its assigned lifetime has been exceeded. (See: certificate
      revocation, expire.)

      Tutorial: The assigned lifetime of an X.509 certificate is stated
      in the certificate itself. (See: validity period.)

   $ certificate extension
      (I) See: extension.

   $ certificate holder
      (D) Synonym for the "subject" of a digital certificate. (Compare:
      certificate owner, certificate user.)

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for the subject of a digital certificate; the term is potentially
      ambiguous. For example, the term could be misunderstood as
      referring to a system entity or component, such as a repository,
      that simply has possession of a copy of the certificate.

   $ certificate management
      (I) The functions that a CA may perform during the lifecycle of a
      digital certificate, including the following:
      -  Acquire and verify data items to bind into the certificate.
      -  Encode and sign the certificate.
      -  Store the certificate in a directory or repository.
      -  Renew, rekey, and update the certificate.
      -  Revoke the certificate and issue a CRL.
      (See: archive management, certificate management, key management,
      security architecture, token management.)

   $ certificate management authority (CMA)
      (D) /U.S. DoD/ Used to mean either a CA or an RA. [DoD7, SP32]

      Deprecated Term: IDOCs SHOULD NOT use this term because it is
      potentially ambiguous, such as in a context involving ICRLs.
      Instead, use CA, RA, or both, depending on what is meant.

   $ certificate owner
      (D) Synonym for the "subject" of a digital certificate. (Compare:
      certificate holder, certificate user.)

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for the subject of a digital certificate; the term is potentially
      ambiguous. For example, the term could refer to a system entity,
      such as a corporation, that has purchased a certificate to operate
      equipment, such as a Web server.

   $ certificate path
      (D) Synonym for "certification path".

      Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
      careless use of "certification path", which is preferred in PKI
      standards (e.g., [X509, R3280]).

   $ certificate policy
      (I) "A named set of rules that indicates the applicability of a
      certificate to a particular community and/or class of application
      with common security requirements." [X509] (Compare: CPS, security
      policy.)

      Example: U.S. DoD's certificate policy [DoD7] defined four classes
      (i.e., assurance levels) for X.509 public-key certificates and
      defines the applicability of those classes. (See: class 2.)

      Tutorial: A certificate policy can help a certificate user to
      decide whether a certificate should be trusted in a particular
      application. "For example, a particular certificate policy might
      indicate applicability of a type of certificate for the
      authentication of electronic data interchange transactions for the
      trading of goods within a given price range." [R3647]

      A v3 X.509 public-key certificate may have a "certificatePolicies"
      extension that lists certificate policies, recognized by the
      issuing CA, that apply to the certificate and govern its use. Each
      policy is denoted by an object identifier and may optionally have
      certificate policy qualifiers. (See: certificate profile.)

      Each SET certificate specifies at least one certificate policy,
      that of the SET root CA. SET uses certificate policy qualifiers to
      point to the actual policy statement and to add qualifying
      policies to the root policy. (See: SET qualifier.)

   $ certificate policy qualifier
      (I) Information that pertains to a certificate policy and is
      included in a "certificatePolicies" extension in a v3 X.509
      public-key certificate.

   $ certificate profile
      (I) A specification (e.g., [DoD7, R3280]) of the format and
      semantics of public-key certificates or attribute certificates,
      constructed for use in a specific application context by selecting
      from among options offered by a broader standard. (Compare:
      protection profile.)

   $ certificate reactivation
      (I) The act or process by which a digital certificate, that a CA
      has designated for revocation but not yet listed on a CRL, is
      returned to the valid state.

   $ certificate rekey
      1. (I) The act or process by which an existing public-key
      certificate has its key value changed by issuing a new certificate
      with a different (usually new) public key. (See: certificate
      renewal, certificate update, rekey.)

      Tutorial: For an X.509 public-key certificate, the essence of
      rekey is that the subject stays the same and a new public key is
      bound to that subject. Other changes are made, and the old

      certificate is revoked, only as required by the PKI and CPS in
      support of the rekey. If changes go beyond that, the process is a
      "certificate update".

      2. (O) /MISSI/ The act or process by which a MISSI CA creates a
      new X.509 public-key certificate that is identical to the old one,
      except the new one has (a) a new, different KEA key or (b) a new,
      different DSS key or (c) new, different KEA and DSS keys. The new
      certificate also has a different serial number and may have a
      different validity period. A new key creation date and maximum key
      lifetime period are assigned to each newly generated key. If a new
      KEA key is generated, that key is assigned a new KMID. The old
      certificate remains valid until it expires, but may not be further
      renewed, rekeyed, or updated.

   $ certificate renewal
      (I) The act or process by which the validity of the binding
      asserted by an existing public-key certificate is extended in time
      by issuing a new certificate. (See: certificate rekey, certificate
      update.)

      Tutorial: For an X.509 public-key certificate, this term means
      that the validity period is extended (and, of course, a new serial
      number is assigned) but the binding of the public key to the
      subject and to other data items stays the same. The other data
      items are changed, and the old certificate is revoked, only as
      required by the PKI and CPS to support the renewal. If changes go
      beyond that, the process is a "certificate rekey" or "certificate
      update".

   $ certificate request
      (D) Synonym for "certification request".

      Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
      careless use of the term "certification request", which is
      preferred in PKI standards (e.g., see PKCS #10).

   $ certificate revocation
      (I) The event that occurs when a CA declares that a previously
      valid digital certificate issued by that CA has become invalid;
      usually stated with an effective date.

      Tutorial: In X.509, a revocation is announced to potential
      certificate users by issuing a CRL that mentions the certificate.
      Revocation and listing on a CRL is only necessary prior to the
      certificate's scheduled expiration.

   $ certificate revocation list (CRL)
      1. (I) A data structure that enumerates digital certificates that
      have been invalidated by their issuer prior to when they were
      scheduled to expire. (See: certificate expiration, delta CRL,
      X.509 certificate revocation list.)

      2. (O) "A signed list indicating a set of certificates that are no
      longer considered valid by the certificate issuer. In addition to
      the generic term CRL, some specific CRL types are defined for CRLs
      that cover particular scopes." [X509]

   $ certificate revocation tree
      (N) A mechanism for distributing notices of certificate
      revocations; uses a tree of hash results that is signed by the
      tree's issuer. Offers an alternative to issuing a CRL, but is not
      supported in X.509. (See: certificate status responder.)

   $ certificate serial number
      1. (I) An integer value that (a) is associated with, and may be
      carried in, a digital certificate; (b) is assigned to the
      certificate by the certificate's issuer; and (c) is unique among
      all the certificates produced by that issuer.

      2. (O) "An integer value, unique within the issuing CA, [that] is
      unambiguously associated with a certificate issued by that CA."
      [X509]

   $ certificate status authority
      (D) /U.S. DoD/ "A trusted entity that provides on-line
      verification to a Relying Party of a subject certificate's
      trustworthiness [should instead say 'validity'], and may also
      provide additional attribute information for the subject
      certificate." [DoD7]

      Deprecated Term: IDOCs SHOULD NOT use this term because it is not
      widely accepted; instead, use "certificate status responder" or
      "OCSP server", or otherwise explain what is meant.

   $ certificate status responder
      (N) /FPKI/ A trusted online server that acts for a CA to provide
      authenticated certificate status information to certificate users
      [FPKI]. Offers an alternative to issuing a CR. (See: certificate
      revocation tree, OCSP.)

   $ certificate update
      (I) The act or process by which non-key data items bound in an
      existing public-key certificate, especially authorizations granted

      to the subject, are changed by issuing a new certificate. (See:
      certificate rekey, certificate renewal.)

      Usage: For an X.509 public-key certificate, the essence of this
      process is that fundamental changes are made in the data that is
      bound to the public key, such that it is necessary to revoke the
      old certificate. (Otherwise, the process is only a "certificate
      rekey" or "certificate renewal".)

   $ certificate user
      1. (I) A system entity that depends on the validity of information
      (such as another entity's public key value) provided by a digital
      certificate. (See: relying party. Compare: /digital certificate/
      subject.)

      Usage: The depending entity may be a human being or an
      organization, or a device or process controlled by a human or
      organization. (See: user.)

      2. (O) "An entity that needs to know, with certainty, the public
      key of another entity." [X509]

      3. (D) Synonym for "subject" of a digital certificate.

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 3; the term could be confused with one of the other two
      definitions given above.

   $ certificate validation
      1. (I) An act or process by which a certificate user establishes
      that the assertions made by a digital certificate can be trusted.
      (See: valid certificate, validate vs. verify.)

      2. (O) "The process of ensuring that a certificate was valid at a
      given time, including possibly the construction and processing of
      a certification path [R4158], and ensuring that all certificates
      in that path were valid (i.e. were not expired or revoked) at that
      given time." [X509]

      Tutorial: To validate a certificate, a certificate user checks
      that the certificate is properly formed and signed and is
      currently in force:
      -  Checks the syntax and semantics: Parses the certificate's
         syntax and interprets its semantics, applying rules specified
         for and by its data fields, such as for critical extensions in
         an X.509 certificate.

      -  Checks the signature: Uses the issuer's public key to verify
         the digital signature of the CA who issued the certificate in
         question. If the verifier obtains the issuer's public key from
         the issuer's own public-key certificate, that certificate
         should be validated, too. That validation may lead to yet
         another certificate to be validated, and so on. Thus, in
         general, certificate validation involves discovering and
         validating a certification path.
      -  Checks currency and revocation: Verifies that the certificate
         is currently in force by checking that the current date and
         time are within the validity period (if that is specified in
         the certificate) and that the certificate is not listed on a
         CRL or otherwise announced as invalid. (The CRLs also must be
         checked by a similar validation process.)

   $ certification
      1. (I) /information system/ Comprehensive evaluation (usually made
      in support of an accreditation action) of an information system's
      technical security features and other safeguards to establish the
      extent to which the system's design and implementation meet a set
      of specified security requirements. [C4009, FP102, SP37] (See:
      accreditation. Compare: evaluation.)

      2. (I) /digital certificate/ The act or process of vouching for
      the truth and accuracy of the binding between data items in a
      certificate. (See: certify.)

      3. (I) /PKI/ The act or process of vouching for the ownership of a
      public key by issuing a public-key certificate that binds the key
      to the name of the entity that possesses the matching private key.
      Besides binding a key with a name, a public-key certificate may
      bind those items with other restrictive or explanatory data items.
      (See: X.509 public-key certificate.)

      4. (O) /SET/ "The process of ascertaining that a set of
      requirements or criteria has been fulfilled and attesting to that
      fact to others, usually with some written instrument. A system
      that has been inspected and evaluated as fully compliant with the
      SET protocol by duly authorized parties and process would be said
      to have been certified compliant." [SET2]

   $ certification authority (CA)
      1. (I) An entity that issues digital certificates (especially
      X.509 certificates) and vouches for the binding between the data
      items in a certificate.

      2. (O) "An authority trusted by one or more users to create and
      assign certificates. Optionally the certification authority may
      create the user's keys." [X509]

      Tutorial: Certificate users depend on the validity of information
      provided by a certificate. Thus, a CA should be someone that
      certificate users trust and that usually holds an official
      position created and granted power by a government, a corporation,
      or some other organization. A CA is responsible for managing the
      life cycle of certificates (see: certificate management) and,
      depending on the type of certificate and the CPS that applies, may
      be responsible for the lifecycle of key pairs associated with the
      certificates (see: key management).

   $ certification authority workstation (CAW)
      (N) A computer system that enables a CA to issue digital
      certificates and supports other certificate management functions
      as required.

   $ certification hierarchy
      1. (I) A tree-structured (loop-free) topology of relationships
      between CAs and the entities to whom the CAs issue public-key
      certificates. (See: hierarchical PKI, hierarchy management.)

      Tutorial: In this structure, one CA is the top CA, the highest
      level of the hierarchy. (See: root, top CA.) The top CA may issue
      public-key certificates to one or more additional CAs that form
      the second-highest level. Each of these CAs may issue certificates
      to more CAs at the third-highest level, and so on. The CAs at the
      second-lowest level issue certificates only to non-CA entities
      that form the lowest level (see: end entity). Thus, all
      certification paths begin at the top CA and descend through zero
      or more levels of other CAs. All certificate users base path
      validations on the top CA's public key.

      2. (I) /PEM/ A certification hierarchy for PEM has three levels of
      CAs [R1422]:
      -  The highest level is the "Internet Policy Registration
         Authority".
      -  A CA at the second-highest level is a "policy certification
         authority".
      -  A CA at the third-highest level is a "certification authority".

      3. (O) /MISSI/ A certification hierarchy for MISSI has three or
      four levels of CAs:
      -  A CA at the highest level, the top CA, is a "policy approving
         authority".

      -  A CA at the second-highest level is a "policy creation
         authority".
      -  A CA at the third-highest level is a local authority called a
         "certification authority".
      -  A CA at the fourth-highest (optional) level is a "subordinate
         certification authority".

      4. (O) /SET/ A certification hierarchy for SET has three or four
      levels of CAs:
      -  The highest level is a "SET root CA".
      -  A CA at the second-highest level is a "brand certification
         authority".
      -  A CA at the third-highest (optional) level is a "geopolitical
         certification authority".
      -  A CA at the fourth-highest level is a "cardholder CA", a
         "merchant CA", or a "payment gateway CA".

   $ certification path
      1. (I) A linked sequence of one or more public-key certificates,
      or one or more public-key certificates and one attribute
      certificate, that enables a certificate user to verify the
      signature on the last certificate in the path, and thus enables
      the user to obtain (from that last certificate) a certified public
      key, or certified attributes, of the system entity that is the
      subject of that last certificate. (See: trust anchor, certificate
      validation, valid certificate.)

      2. (O) "An ordered sequence of certificates of objects in the
      [X.500 Directory Information Tree] which, together with the public
      key of the initial object in the path, can be processed to obtain
      that of the final object in the path." [R3647, X509]

      Tutorial: The list is "linked" in the sense that the digital
      signature of each certificate (except possibly the first) is
      verified by the public key contained in the preceding certificate;
      i.e., the private key used to sign a certificate and the public
      key contained in the preceding certificate form a key pair that
      has previously been bound to the authority that signed.

      The path is the "list of certificates needed to [enable] a
      particular user to obtain the public key [or attributes] of
      another [user]." [X509] Here, the word "particular" points out
      that a certification path that can be validated by one certificate
      user might not be able to be validated by another. That is because
      either the first certificate needs to be a trusted certificate or
      the signature on the first certificate needs to be verifiable by a
      trusted key (e.g., a root key), but such trust is established only

      relative to a "particular" (i.e., specific) user, not absolutely
      for all users.

   $ certification policy
      (D) Synonym for either "certificate policy" or "certification
      practice statement".

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      either of those terms; that would be duplicative and would mix
      concepts in a potentially misleading way. Instead, use either
      "certificate policy" or "certification practice statement",
      depending on what is meant.

   $ certification practice statement (CPS)
      (I) "A statement of the practices which a certification authority
      employs in issuing certificates." [DSG, R3647] (See: certificate
      policy.)

      Tutorial: A CPS is a published security policy that can help a
      certificate user to decide whether a certificate issued by a
      particular CA can be trusted enough to use in a particular
      application. A CPS may be (a) a declaration by a CA of the details
      of the system and practices it uses in its certificate management
      operations, (b) part of a contract between the CA and an entity to
      whom a certificate is issued, (c) a statute or regulation
      applicable to the CA, or (d) a combination of these types
      involving multiple documents. [DSG]

      A CPS is usually more detailed and procedurally oriented than a
      certificate policy. A CPS applies to a particular CA or CA
      community, while a certificate policy applies across CAs or
      communities. A CA with its single CPS may support multiple
      certificate policies, which may be used for different application
      purposes or by different user communities. On the other hand,
      multiple CAs, each with a different CPS, may support the same
      certificate policy. [R3647]

   $ certification request
      (I) An algorithm-independent transaction format (e.g., PKCS #10,
      RFC 4211) that contains a DN, and a public key or, optionally, a
      set of attributes, collectively signed by the entity requesting
      certification, and sent to a CA, which transforms the request to
      an X.509 public-key certificate or another type of certificate.

   $ certify
      1. (I) Issue a digital certificate and thus vouch for the truth,
      accuracy, and binding between data items in the certificate (e.g.,
      "X.509 public-key certificate"), such as the identity of the

      certificate's subject and the ownership of a public key. (See:
      certification.)

      Usage: To "certify a public key" means to issue a public-key
      certificate that vouches for the binding between the certificate's
      subject and the key.

      2. (I) The act by which a CA uses measures to verify the truth,
      accuracy, and binding between data items in a digital certificate.

      Tutorial: A description of the measures used for verification
      should be included in the CA's CPS.

   $ CFB
      (N) See: cipher feedback.

   $ chain
      (D) See: trust chain.

   $ Challenge Handshake Authentication Protocol (CHAP)
      (I) A peer entity authentication method (employed by PPP and other
      protocols, e.g., RFC 3720) that uses a randomly generated
      challenge and requires a matching response that depends on a
      cryptographic hash of some combination of the challenge and a
      secret key. [R1994] (See: challenge-response, PAP.)

   $ challenge-response
      (I) An authentication process that verifies an identity by
      requiring correct authentication information to be provided in
      response to a challenge. In a computer system, the authentication
      information is usually a value that is required to be computed in
      response to an unpredictable challenge value, but it might be just
      a password.

   $ Challenge-Response Authentication Mechanism (CRAM)
      (I) /IMAP4/ A mechanism [R2195], intended for use with IMAP4
      AUTHENTICATE, by which an IMAP4 client uses a keyed hash [R2104]
      to authenticate itself to an IMAP4 server. (See: POP3 APOP.)

      Tutorial: The server includes a unique time stamp in its ready
      response to the client. The client replies with the client's name
      and the hash result of applying MD5 to a string formed from
      concatenating the time stamp with a shared secret that is known
      only to the client and the server.

   $ channel
      1. (I) An information transfer path within a system. (See: covert
      channel.)

      2. (O) "A subdivision of the physical medium allowing possibly
      shared independent uses of the medium." (RFC 3753)

   $ channel capacity
      (I) The total capacity of a link to carry information; usually
      expressed in bits per second. (RFC 3753) (Compare: bandwidth.)

      Tutorial: Within a given bandwidth, the theoretical maximum
      channel capacity is given by Shannon's Law. The actual channel
      capacity is determined by the bandwidth, the coding system used,
      and the signal-to-noise ratio.

   $ CHAP
      (I) See: Challenge Handshake Authentication Protocol.

   $ checksum
      (I) A value that (a) is computed by a function that is dependent
      on the contents of a data object and (b) is stored or transmitted
      together with the object, for detecting changes in the data. (See:
      cyclic redundancy check, data integrity service, error detection
      code, hash, keyed hash, parity bit, protected checksum.)

      Tutorial: To gain confidence that a data object has not been
      changed, an entity that later uses the data can independently
      recompute the checksum value and compare the result with the value
      that was stored or transmitted with the object.

      Computer systems and networks use checksums (and other mechanisms)
      to detect accidental changes in data. However, active wiretapping
      that changes data could also change an accompanying checksum to
      match the changed data. Thus, some checksum functions by
      themselves are not good countermeasures for active attacks. To
      protect against active attacks, the checksum function needs to be
      well-chosen (see: cryptographic hash), and the checksum result
      needs to be cryptographically protected (see: digital signature,
      keyed hash).

   $ Chinese wall policy
      (I) A security policy to prevent conflict of interest caused by an
      entity (e.g., a consultant) interacting with competing firms.
      (See: Brewer-Nash model.)

      Tutorial: All information is categorized into mutually exclusive
      conflict-of-interest classes I(1), I(2), ..., I(M), and each firm
      F(1), F(2), ..., F(N) belongs to exactly one class. The policy
      states that if a consultant has access to class I(i) information
      from a firm in that class, then the consultant may not access
      information from another firm in that same class, but may access

      information from another firm that is in a different class. Thus,
      the policy creates a barrier to communication between firms that
      are in the same conflict-of-interest class. Brewer and Nash
      modeled enforcement of this policy [BN89], including dealing with
      policy violations that could occur because two or more consultants
      work for the same firm.

   $ chosen-ciphertext attack
      (I) A cryptanalysis technique in which the analyst tries to
      determine the key from knowledge of plain text that corresponds to
      cipher text selected (i.e., dictated) by the analyst.

   $ chosen-plaintext attack
      (I) A cryptanalysis technique in which the analyst tries to
      determine the key from knowledge of cipher text that corresponds
      to plain text selected (i.e., dictated) by the analyst.

   $ CIAC
      (O) See: Computer Incident Advisory Capability.

   $ CIK
      (N) See: cryptographic ignition key.

   $ cipher
      (I) A cryptographic algorithm for encryption and decryption.

   $ cipher block chaining (CBC)
      (N) A block cipher mode that enhances ECB mode by chaining
      together blocks of cipher text it produces. [FP081] (See: block
      cipher, [R1829], [R2405], [R2451], [SP38A].)

      Tutorial: This mode operates by combining (exclusive OR-ing) the
      algorithm's ciphertext output block with the next plaintext block
      to form the next input block for the algorithm.

   $ cipher feedback (CFB)
      (N) A block cipher mode that enhances ECB mode by chaining
      together the blocks of cipher text it produces and operating on
      plaintext segments of variable length less than or equal to the
      block length. [FP081] (See: block cipher, [SP38A].)

      Tutorial: This mode operates by using the previously generated
      ciphertext segment as the algorithm's input (i.e., by "feeding
      back" the cipher text) to generate an output block, and then
      combining (exclusive OR-ing) that output block with the next
      plaintext segment (block length or less) to form the next
      ciphertext segment.

   $ cipher text
      1. (I) /noun/ Data that has been transformed by encryption so that
      its semantic information content (i.e., its meaning) is no longer
      intelligible or directly available. (See: ciphertext. Compare:
      clear text, plain text.)

      2. (O) "Data produced through the use of encipherment. The
      semantic content of the resulting data is not available."
      [I7498-2]

   $ ciphertext
      1. (O) /noun/ Synonym for "cipher text" [I7498-2].

      2. (I) /adjective/ Referring to cipher text. Usage: Commonly used
      instead of "cipher-text". (Compare: cleartext, plaintext.)

   $ ciphertext auto-key (CTAK)
      (D) "Cryptographic logic that uses previous cipher text to
      generate a key stream." [C4009, A1523] (See: KAK.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it is neither
      well-known nor precisely defined. Instead, use terms associated
      with modes that are defined in standards, such as CBC, CFB, and
      OFB.

   $ ciphertext-only attack
      (I) A cryptanalysis technique in which the analyst tries to
      determine the key solely from knowledge of intercepted cipher text
      (although the analyst may also know other clues, such as the
      cryptographic algorithm, the language in which the plain text was
      written, the subject matter of the plain text, and some probable
      plaintext words.)

   $ ciphony
      (O) The process of encrypting audio information.

   $ CIPSO
      (I) See: Common IP Security Option.

   $ CKL
      (I) See: compromised key list.

   $ Clark-Wilson model
      (N) A security model [Clark] to maintain data integrity in the
      commercial world. (Compare: Bell-LaPadula model.)

   $ class 2, 3, 4, 5
      (O) /U.S. DoD/ Assurance levels for PKIs, and for X.509 public-key
      certificates issued by a PKI. [DoD7] (See: "first law" under
      "Courtney's laws".)
      -  "Class 2": Intended for applications handling unclassified,
         low-value data in minimally or moderately protected
         environments.
      -  "Class 3": Intended for applications handling unclassified,
         medium-value data in moderately protected environments, or
         handling unclassified or high-value data in highly protected
         environments, and for discretionary access control of
         classified data in highly protected environments.
      -  "Class 4": Intended for applications handling unclassified,
         high-value data in minimally protected environments.
      -  "Class 5": Intended for applications handling classified data
         in minimally protected environments, and for authentication of
         material that would affect the security of classified systems.

      The environments are defined as follows:
      -  "Highly protected environment": Networks that are protected
         either with encryption devices approved by NSA for protection
         of classified data or via physical isolation, and that are
         certified for processing system-high classified data, where
         exposure of unencrypted data is limited to U.S. citizens
         holding appropriate security clearances.
      -  "Moderately protected environment":
         -- Physically isolated unclassified, unencrypted networks in
            which access is restricted based on legitimate need.
         -- Networks protected by NSA-approved, type 1 encryption,
            accessible by U.S.-authorized foreign nationals.
      -  "Minimally protected environments": Unencrypted networks
         connected to either the Internet or NIPRNET, either directly or
         via a firewall.

   $ Class A1, B3, B2, B1, C2, or C1 computer system
      (O) /TCSEC/ See: Tutorial under "Trusted Computer System
      Evaluation Criteria".

   $ classification
      1. (I) A grouping of classified information to which a
      hierarchical, restrictive security label is applied to increase
      protection of the data from unauthorized disclosure. (See:
      aggregation, classified, data confidentiality service. Compare:
      category, compartment.)

      2. (I) An authorized process by which information is determined to
      be classified and assigned to a security level. (Compare:
      declassification.)

      Usage: Usually understood to involve data confidentiality, but
      IDOCs SHOULD make this clear when data also is sensitive in other
      ways and SHOULD use other terms for those other sensitivity
      concepts. (See: sensitive information, data integrity.)

   $ classification label
      (I) A security label that tells the degree of harm that will
      result from unauthorized disclosure of the labeled data, and may
      also tell what countermeasures are required to be applied to
      protect the data from unauthorized disclosure. Example: IPSO.
      (See: classified, data confidentiality service. Compare: integrity
      label.)

      Usage: Usually understood to involve data confidentiality, but
      IDOCs SHOULD make this clear when data also is sensitive in other
      ways and SHOULD use other terms for those other sensitivity
      concepts. (See: sensitive information, data integrity.)

   $ classification level
      (I) A hierarchical level of protection (against unauthorized
      disclosure) that is required to be applied to certain classified
      data. (See: classified. Compare: security level.)

      Usage: Usually understood to involve data confidentiality, but
      IDOCs SHOULD make this clear when data also is sensitive in other
      ways and SHOULD use other terms for those other sensitivity
      concepts. (See: sensitive information, data integrity.)

   $ classified
      1. (I) Refers to information (stored or conveyed, in any form)
      that is formally required by a security policy to receive data
      confidentiality service and to be marked with a security label
      (which, in some cases, might be implicit) to indicate its
      protected status. (See: classify, collateral information, SAP,
      security level. Compare: unclassified.)

      Usage: Usually understood to involve data confidentiality, but
      IDOCs SHOULD make this clear when data also is sensitive in other
      ways and SHOULD use other terms for those other sensitivity
      concepts. (See: sensitive information, data integrity.)

      Mainly used by national governments, especially by the military,
      but the underlying concept also applies outside of governments.

      2. (O) /U.S. Government/ "Information that has been determined
      pursuant to Executive Order 12958 or any predecessor Order, or by
      the Atomic Energy Act of 1954, as amended, to require protection

      against unauthorized disclosure and is marked to indicate its
      classified status." [C4009]

   $ classify
      (I) To officially designate an information item or type of
      information as being classified and assigned to a specific
      security level. (See: classified, declassify, security level.)

   $ clean system
      (I) A computer system in which the operating system and
      application system software and files have been freshly installed
      from trusted software distribution media. (Compare: secure state.)

   $ clear
      (D) /verb/ Synonym for "erase". [C4009]

      Deprecated Definition: IDOCs SHOULD NOT use the term with this
      definition; that could be confused with "clear text" in which
      information is directly recoverable.

   $ clear text
      1. (I) /noun/ Data in which the semantic information content
      (i.e., the meaning) is intelligible or is directly available,
      i.e., not encrypted. (See: cleartext, in the clear. Compare:
      cipher text, plain text.)

      2. (O) /noun/ "Intelligible data, the semantic content of which is
      available." [I7498-2]

      3. (D) /noun/ Synonym for "plain text".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "plain text", because the plain text that is input to an
      encryption operation may itself be cipher text that was output
      from a previous encryption operation. (See: superencryption.)

   $ clearance
      See: security clearance.

   $ clearance level
      (I) The security level of information to which a security
      clearance authorizes a person to have access.

   $ cleartext
      1. (O) /noun/ Synonym for "clear text" [I7498-2].

      2. (I) /adjective/ Referring to clear text. Usage: Commonly used
      instead of "clear-text". (Compare: ciphertext, plaintext.)

      3. (D) /adjective/ Synonym for "plaintext".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "plaintext", because the plaintext data that is input to an
      encryption operation may itself be ciphertext data that was output
      from a previous encryption operation. (See: superencryption.)

   $ CLEF
      (N) See: commercially licensed evaluation facility.

   $ client
      (I) A system entity that requests and uses a service provided by
      another system entity, called a "server". (See: server.)

      Tutorial: Usually, it is understood that the client and server are
      automated components of the system, and the client makes the
      request on behalf of a human user. In some cases, the server may
      itself be a client of some other server.

   $ client-server system
      (I) A distributed system in which one or more entities, called
      clients, request a specific service from one or more other
      entities, called servers, that provide the service to the clients.

      Example: The Word Wide Web, in which component servers provide
      information that is requested by component clients called
      "browsers".

   $ CLIPPER
      (N) An integrated microcircuit (in MYK-7x series manufactured by
      Mykotronx, Inc.) that implements SKIPJACK, has a non-deterministic
      random number generator, and supports key escrow. (See: Escrowed
      Encryption Standard. Compare: CLIPPER.)

      Tutorial: The chip was mainly intended for protecting
      telecommunications over the public switched network. The key
      escrow scheme for the chip involves a SKIPJACK key that is common
      to all chips and that protects the unique serial number of the
      chip, and a second SKIPJACK key unique to the chip that protects
      all data encrypted by the chip. The second key is escrowed as
      split key components held by NIST and the U.S. Treasury
      Department.

   $ closed security environment
      (O) /U.S. DoD/ A system environment that meets both of the
      following conditions: (a) Application developers (including
      maintainers) have sufficient clearances and authorizations to
      provide an acceptable presumption that they have not introduced

      malicious logic. (b) Configuration control provides sufficient
      assurance that system applications and the equipment they run on
      are protected against the introduction of malicious logic prior to
      and during the operation of applications. [NCS04] (See: "first
      law" under "Courtney's laws". Compare: open security environment.)

   $ CMA
      (D) See: certificate management authority.

   $ CMAC
      (N) A message authentication code [SP38B] that is based on a
      symmetric block cipher. (See: block cipher.)

      Derivation: Cipher-based MAC. (Compare: HMAC.)

      Tutorial: Because CMAC is based on approved, symmetric-key block
      ciphers, such as AES, CMAC can be considered a mode of operation
      for those block ciphers. (See: mode of operation.)

   $ CMCS
      (O) See: COMSEC Material Control System.

   $ CMM
      (N) See: Capability Maturity Model.

   $ CMS
      (I) See: Cryptographic Message Syntax.

   $ code
      1. (I) A system of symbols used to represent information, which
      might originally have some other representation. Examples: ASCII,
      BER, country code, Morse code. (See: encode, object code, source
      code.)

      Deprecated Abbreviation: To avoid confusion with definition 1,
      IDOCs SHOULD NOT use "code" as an abbreviation of "country code",
      "cyclic redundancy code", "Data Authentication Code", "error
      detection code", or "Message Authentication Code". To avoid
      misunderstanding, use the fully qualified term in these other
      cases, at least at the point of first usage.

      2. (I) /cryptography/ An encryption algorithm based on
      substitution; i.e., a system for providing data confidentiality by
      using arbitrary groups (called "code groups") of letters, numbers,
      or symbols to represent units of plain text of varying length.
      (See: codebook, cryptography.)

      Deprecated Usage: To avoid confusion with definition 1, IDOCs
      SHOULD NOT use "code" as a synonym for any of the following terms:
      (a) "cipher", "hash", or other words that mean "a cryptographic
      algorithm"; (b) "cipher text"; or (c) "encrypt", "hash", or other
      words that refer to applying a cryptographic algorithm.

      3. (I) An algorithm based on substitution, but used to shorten
      messages rather than to conceal their content.

      4. (I) /computer programming/ To write computer software. (See:
      object code, source code.)

      Deprecated Abbreviation: To avoid confusion with definition 1,
      IDOCs SHOULD NOT use "code" as an abbreviation of "object code" or
      "source code". To avoid misunderstanding, use the fully qualified
      term in these other cases, at least at the point of first usage.

   $ code book
      1. (I) Document containing a systematically arranged list of
      plaintext units and their ciphertext equivalents. [C4009]

      2. (I) An encryption algorithm that uses a word substitution
      technique. [C4009] (See: code, ECB.)

   $ code signing
      (I) A security mechanism that uses a digital signature to provide
      data integrity and data origin authentication for software that is
      being distributed for use. (See: mobile code, trusted
      distribution.)

      Tutorial: In some cases, the signature on a software module may
      imply some assertion that the signer makes about the software. For
      example, a signature may imply that the software has been
      designed, developed, or tested according to some criterion.

   $ code word
      (O) /U.S. Government/ A single word that is used as a security
      label (usually applied to classified information) but which itself
      has a classified meaning. (See: classified, /U.S. Government/
      security label.)

   $ COI
      (I) See: community of interest.

   $ cold start
      (N) /cryptographic module/ A procedure for initially keying
      cryptographic equipment. [C4009]

   $ collateral information
      (O) /U.S. Government/ Information that is classified but is not
      required to be protected by an SAP. (See: /U.S. Government/
      classified.)

   $ color change
      (I) In a system being operated in periods-processing mode, the act
      of purging all information from one processing period and then
      changing over to the next processing period. (See: BLACK, RED.)

   $ Commercial COMSEC Evaluation Program (CCEP)
      (O) "Relationship between NSA and industry in which NSA provides
      the COMSEC expertise (i.e., standards, algorithms, evaluations,
      and guidance) and industry provides design, development, and
      production capabilities to produce a type 1 or type 2 product."
      [C4009]

   $ commercially licensed evaluation facility (CLEF)
      (N) An organization that has official approval to evaluate the
      security of products and systems under the Common Criteria, ITSEC,
      or some other standard. (Compare: KLIF.)

   $ Committee on National Security Systems (CNSS)
      (O) /U.S. Government/ A Government, interagency, standing
      committee of the President's Critical Infrastructure Protection
      Board. The CNSS is chaired by the Secretary of Defense and
      provides a forum for the discussion of policy issues, sets
      national policy, and promulgates direction, operational
      procedures, and guidance for the security of national security
      systems. The Secretary of Defense and the Director of Central
      Intelligence are responsible for developing and overseeing the
      implementation of Government-wide policies, principles, standards,
      and guidelines for the security of systems that handle national
      security information.

   $ Common Criteria for Information Technology Security
      (N) A standard for evaluating information technology (IT) products
      and systems. It states requirements for security functions and for
      assurance measures. [CCIB] (See: CLEF, EAL, packages, protection
      profile, security target, TOE. Compare: CMM.)

      Tutorial: Canada, France, Germany, the Netherlands, the United
      Kingdom, and the United States (NIST and NSA) began developing
      this standard in 1993, based on the European ITSEC, the Canadian
      Trusted Computer Product Evaluation Criteria (CTCPEC), and the
      U.S. "Federal Criteria for Information Technology Security" and
      its precursor, the TCSEC. Work was done in cooperation with
      ISO/IEC Joint Technical Committee 1 (Information Technology),

      Subcommittee 27 (Security Techniques), Working Group 3 (Security
      Criteria). Version 2.0 of the Criteria has been issued as ISO's
      International Standard 15408. The U.S. Government intends this
      standard to supersede both the TCSEC and FIPS PUB 140. (See:
      NIAP.)

      The standard addresses data confidentiality, data integrity, and
      availability and may apply to other aspects of security. It
      focuses on threats to information arising from human activities,
      malicious or otherwise, but may apply to non-human threats. It
      applies to security measures implemented in hardware, firmware, or
      software. It does not apply to (a) administrative security not
      related directly to technical security, (b) technical physical
      aspects of security such as electromagnetic emanation control, (c)
      evaluation methodology or administrative and legal framework under
      which the criteria may be applied, (d) procedures for use of
      evaluation results, or (e) assessment of inherent qualities of
      cryptographic algorithms.

      Part 1, Introduction and General Model, defines general concepts
      and principles of IT security evaluation; presents a general model
      of evaluation; and defines constructs for expressing IT security
      objectives, for selecting and defining IT security requirements,
      and for writing high-level specifications for products and
      systems.

      Part 2, Security Functional Requirements, contains a catalog of
      well-defined and well-understood functional requirement statements
      that are intended to be used as a standard way of expressing the
      security requirements for IT products and systems.

      Part 3, Security Assurance Requirements, contains a catalog of
      assurance components for use as a standard way of expressing such
      requirements for IT products and systems, and defines evaluation
      criteria for protection profiles and security targets.

   $ Common IP Security Option (CIPSO)
      (I) See: secondary definition under "IPSO".

   $ common name
      (N) A character string that (a) may be a part of the X.500 DN of a
      Directory object ("commonName" attribute), (b) is a (possibly
      ambiguous) name by which the object is commonly known in some
      limited scope (such as an organization), and (c) conforms to the
      naming conventions of the country or culture with which it is
      associated. [X520] (See: "subject" and "issuer" under "X.509
      public-key certificate".)

      Examples: "Dr. Albert Einstein", "The United Nations", and "12-th
      Floor Laser Printer".

   $ communications cover
      (N) "Concealing or altering of characteristic communications
      patterns to hide information that could be of value to an
      adversary." [C4009] (See: operations security, traffic-flow
      confidentiality, TRANSEC.)

   $ communication security (COMSEC)
      (I) Measures that implement and assure security services in a
      communication system, particularly those that provide data
      confidentiality and data integrity and that authenticate
      communicating entities.

      Usage: COMSEC is usually understood to include (a) cryptography
      and its related algorithms and key management methods and
      processes, devices that implement those algorithms and processes,
      and the lifecycle management of the devices and keying material.
      Also, COMSEC is sometimes more broadly understood as further
      including (b) traffic-flow confidentiality, (c) TRANSEC, and (d)
      steganography [Kahn]. (See: cryptology, signal security.)

   $ community of interest (COI)
      1. (I) A set of entities that operate under a common security
      policy. (Compare: domain.)

      2. (I) A set of entities that exchange information collaboratively
      for some purpose.

   $ community risk
      (N) Probability that a particular vulnerability will be exploited
      within an interacting population and adversely affect some members
      of that population. [C4009] (See: Morris worm, risk.)

   $ community string
      (I) A community name in the form of an octet string that serves as
      a cleartext password in SNMP version 1 (RFC 1157) and version 2
      (RFC 1901). (See: password, Simple Network Management Protocol.)

      Tutorial: The SNMPv1 and SNMPv2 protocols have been declared
      "historic" and have been replaced by the more secure SNMPv3
      standard (RFCs 3410-3418), which does not use cleartext passwords.

   $ compartment
      1. (I) A grouping of sensitive information items that require
      special access controls beyond those normally provided for the
      basic classification level of the information. (See: compartmented
      security mode. Compare: category, classification.)

      Usage: The term is usually understood to include the special
      handling procedures to be used for the information.

      2. (I) Synonym for "category".

      Deprecated Usage: This Glossary defines "category" with a slightly
      narrower meaning than "compartment". That is, a security label is
      assigned to a category because the data owner needs to handle the
      data as a compartment. However, a compartment could receive
      special protection in a system without being assigned a category
      label.

   $ compartmented security mode
      (N) A mode of system operation wherein all users having access to
      the system have the necessary security clearance for the single,
      hierarchical classification level of all data handled by the
      system, but some users do not have the clearance for a non-
      hierarchical category of some data handled by the system. (See:
      category, /system operation/ under "mode", protection level,
      security clearance.)

      Usage: Usually abbreviated as "compartmented mode". This term was
      defined in U.S. Government policy on system accreditation. In this
      mode, a system may handle (a) a single hierarchical classification
      level and (b) multiple non-hierarchical categories within that
      level.

   $ Compartments field
      (I) A 16-bit field (the "C field") that specifies compartment
      values in the security option (option type 130) of version 4 IP's
      datagram header format. The valid field values are assigned by the
      U.S. Government, as specified in RFC 791.

      Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "C
      field"; the abbreviation is potentially ambiguous. Instead, use
      "Compartments field".

   $ component
      See: system component.

   $ compression
      (I) A process that encodes information in a way that minimizes the
      number of resulting code symbols and thus reduces storage space or
      transmission time.

      Tutorial: A data compression algorithm may be "lossless", i.e.,
      retain all information that was encoded in the data, so that
      decompression can recover all the information; or an algorithm may
      be "lossy". Text usually needs to be compressed losslessly, but
      images are often compressed with lossy schemes.

      Not all schemes that encode information losslessly for machine
      processing are efficient in terms of minimizing the number of
      output bits. For example, ASCII encoding is lossless, but ASCII
      data can often be losslessly reencoded in fewer bits with other
      schemes. These more efficient schemes take advantage of some sort
      of inherent imbalance, redundancy, or repetition in the data, such
      as by replacing a character string in which all characters are the
      same by a shorter string consisting of only the single character
      and a character count.

      Lossless compression schemes cannot effectively reduce the number
      of bits in cipher text produced by a strong encryption algorithm,
      because the cipher text is essentially a pseudorandom bit string
      that does not contain patterns susceptible to reencoding.
      Therefore, protocols that offer both encryption and compression
      services (e.g., SSL) need to perform the compression operation
      before the encryption operation.

   $ compromise
      See: data compromise, security compromise.

   $ compromise recovery
      (I) The process of regaining a secure state for a system after
      detecting that the system has experienced a security compromise.

   $ compromised key list (CKL)
      (N) /MISSI/ A list that identifies keys for which unauthorized
      disclosure or alteration may have occurred. (See: compromise.)

      Tutorial: A CKL is issued by a CA, like a CRL is issued. But a CKL
      lists only KMIDs, not subjects that hold the keys, and not
      certificates in which the keys are bound.

   $ COMPUSEC
      (I) See: computer security.

   $ computer emergency response team (CERT)
      (I) An organization that studies computer and network INFOSEC in
      order to provide incident response services to victims of attacks,
      publish alerts concerning vulnerabilities and threats, and offer
      other information to help improve computer and network security.
      (See: CSIRT, security incident.)

      Examples: CERT Coordination Center at Carnegie Mellon University
      (sometimes called "the" CERT); CIAC.

   $ Computer Incident Advisory Capability (CIAC)
      (O) The centralized CSIRT of the U.S. Department of Energy; a
      member of FIRST.

   $ computer network
      (I) A collection of host computers together with the subnetwork or
      internetwork through which they can exchange data.

      Usage: This definition is intended to cover systems of all sizes
      and types, ranging from the complex Internet to a simple system
      composed of a personal computer dialing in as a remote terminal of
      another computer.

   $ computer platform
      (I) A combination of computer hardware and an operating system
      (which may consist of software, firmware, or both) for that
      hardware. (Compare: computer system.)

   $ computer security (COMPUSEC)
      1. (I) Measures to implement and assure security services in a
      computer system, particularly those that assure access control
      service.

      Usage: Usually refers to internal controls (functions, features,
      and technical characteristics) that are implemented in software
      (especially in operating systems); sometimes refers to internal
      controls implemented in hardware; rarely used to refer to external
      controls.

      2. (O) "The protection afforded to an automated information system
      in order to attain the applicable objectives of preserving the
      integrity, availability and confidentiality of information system
      resources (includes hardware, software, firmware,
      information/data, and telecommunications)." [SP12]

   $ computer security incident response team (CSIRT)
      (I) An organization "that coordinates and supports the response to
      security incidents that involve sites within a defined
      constituency." [R2350] (See: CERT, FIRST, security incident.)

      Tutorial: To be considered a CSIRT, an organization must do as
      follows: (a) Provide a (secure) channel for receiving reports
      about suspected security incidents. (b) Provide assistance to
      members of its constituency in handling the incidents. (c)
      Disseminate incident-related information to its constituency and
      other involved parties.

   $ computer security object
      (I) The definition or representation of a resource, tool, or
      mechanism used to maintain a condition of security in computerized
      environments. Includes many items referred to in standards that
      are either selected or defined by separate user communities.
      [CSOR] (See: object identifier, Computer Security Objects
      Register.)

   $ Computer Security Objects Register (CSOR)
      (N) A service operated by NIST is establishing a catalog for
      computer security objects to provide stable object definitions
      identified by unique names. The use of this register will enable
      the unambiguous specification of security parameters and
      algorithms to be used in secure data exchanges. (See: object
      identifier.)

      Tutorial: The CSOR follows registration guidelines established by
      the international standards community and ANSI. Those guidelines
      establish minimum responsibilities for registration authorities
      and assign the top branches of an international registration
      hierarchy. Under that international registration hierarchy, the
      CSOR is responsible for the allocation of unique identifiers under
      the branch: {joint-iso-ccitt(2) country(16) us(840)
      organization(1) gov(101) csor(3)}.

   $ computer system
      (I) Synonym for "information system", or a component thereof.
      (Compare: computer platform.)

   $ Computers At Risk
      (O) The 1991 report [NRC91] of the System Security Study
      Committee, sponsored by the U.S. National Academy of Sciences and
      supported by the Defense Advanced Research Projects Agency of the
      U.S. DoD. It made many recommendations for industry and
      governments to improve computer security and trustworthiness. Some
      of the most important recommendations (e.g., establishing an

      Information Security Foundation chartered by the U.S. Government)
      have not been implemented at all, and others (e.g., codifying
      Generally Accepted System Security Principles similar to
      accounting principles) have been implemented but not widely
      adopted [SP14, SP27].

   $ COMSEC
      (I) See: communication security.

   $ COMSEC account
      (O) /U.S. Government/ "Administrative entity, identified by an
      account number, used to maintain accountability, custody, and
      control of COMSEC material." [C4009] (See: COMSEC custodian.)

   $ COMSEC accounting
      (O) /U.S. Government/ The process of creating, collecting, and
      maintaining data records that describe the status and custody of
      designated items of COMSEC material. (See: accounting legend
      code.)

      Tutorial: Almost any secure information system needs to record a
      security audit trail, but a system that manages COMSEC material
      needs to record additional data about the status and custody of
      COMSEC items.
      -  COMSEC tracking: The process of automatically collecting,
         recording, and managing information that describes the status
         of designated items of COMSEC material at all times during each
         product's lifecycle.
      -  COMSEC controlling: The process of supplementing tracking data
         with custody data, which consists of explicit acknowledgements
         of system entities that they (a) have received specific COMSEC
         items and (b) are responsible for preventing exposure of those
         items.

      For example, a key management system that serves a large customer
      base needs to record tracking data for the same reasons that a
      national parcel delivery system does, i.e., to answer the question
      "Where is that thing now?". If keys are encrypted immediately upon
      generation and handled only in BLACK form between the point of
      generation and the point of use, then tracking may be all that is
      needed. However, in cases where keys are handled at least partly
      in RED form and are potentially subject to exposure, then tracking
      needs to be supplemented by controlling.

      Data that is used purely for tracking need be retained only
      temporarily, until an item's status changes. Data that is used for
      controlling is retained indefinitely to ensure accountability and
      support compromise recovery.

   $ COMSEC boundary
      (N) "Definable perimeter encompassing all hardware, firmware, and
      software components performing critical COMSEC functions, such as
      key generation and key handling and storage." [C4009] (Compare:
      cryptographic boundary.)

   $ COMSEC custodian
      (O) /U.S. Government/ "Individual designated by proper authority
      to be responsible for the receipt, transfer, accounting,
      safeguarding, and destruction of COMSEC material assigned to a
      COMSEC account." [C4009]

   $ COMSEC material
      (N) /U.S. Government/ Items designed to secure or authenticate
      communications or information in general; these items include (but
      are not limited to) keys; equipment, devices, documents, firmware,
      and software that embodies or describes cryptographic logic; and
      other items that perform COMSEC functions. [C4009] (Compare:
      keying material.)

   $ COMSEC Material Control System (CMCS)
      (O) /U.S. Government/ "Logistics and accounting system through
      which COMSEC material marked 'CRYPTO' is distributed, controlled,
      and safeguarded." [C4009] (See: COMSEC account, COMSEC custodian.)

   $ confidentiality
      See: data confidentiality.

   $ concealment system
      (O) "A method of achieving confidentiality in which sensitive
      information is hidden by embedding it in irrelevant data." [NCS04]
      (Compare: steganography.)

   $ configuration control
      (I) The process of regulating changes to hardware, firmware,
      software, and documentation throughout the development and
      operational life of a system. (See: administrative security,
      harden, trusted distribution.)

      Tutorial: Configuration control helps protect against unauthorized
      or malicious alteration of a system and thus provides assurance of
      system integrity. (See: malicious logic.)

   $ confinement property
      (N) /formal model/ Property of a system whereby a subject has
      write access to an object only if the classification of the object
      dominates the clearance of the subject. (See: *-property, Bell-
      LaPadula model.)

   $ constraint
      (I) /access control/ A limitation on the function of an identity,
      role, or privilege. (See: rule-based access control.)

      Tutorial: In effect, a constraint is a form of security policy and
      may be either static or dynamic:
      -  "Static constraint": A constraint that must be satisfied at the
         time the policy is defined, and then continues to be satisfied
         until the constraint is removed.
      -  "Dynamic constraint": A constraint that may be defined to apply
         at various times that the identity, role, or other object of
         the constraint is active in the system.

   $ content filter
      (I) /World Wide Web/ Application software used to prevent access
      to certain Web servers, such as by parents who do not want their
      children to access pornography. (See: filter, guard.)

      Tutorial: The filter is usually browser-based, but could be part
      of an intermediate cache server. The two basic content filtering
      techniques are (a) to block a specified list of URLs and (b) to
      block material that contains specified words and phrases.

   $ contingency plan
      (I) A plan for emergency response, backup operations, and post-
      disaster recovery in a system as part of a security program to
      ensure availability of critical system resources and facilitate
      continuity of operations in a crisis. [NCS04] (See: availability.)

   $ control zone
      (O) "The space, expressed in feet of radius, surrounding equipment
      processing sensitive information, that is under sufficient
      physical and technical control to preclude an unauthorized entry
      or compromise." [NCSSG] (Compare: inspectable space, TEMPEST
      zone.)

   $ controlled access protection
      (O) /TCSEC/ The level of evaluation criteria for a C2 computer
      system.

      Tutorial: The major features of the C2 level are individual
      accountability, audit, access control, and object reuse.

   $ controlled cryptographic item (CCI)
      (O) /U.S. Government/ "Secure telecommunications or information
      handling equipment, or associated cryptographic component, that is
      unclassified but governed by a special set of control
      requirements." [C4009] (Compare: EUCI.)

      Tutorial: This category of equipment was established in 1985 to
      promote broad use of secure equipment for protecting both
      classified and unclassified information in the national interest.
      CCI equipment uses a classified cryptographic logic, but the
      hardware or firmware embodiment of that logic is unclassified.
      Drawings, software implementations, and other descriptions of that
      logic remain classified. [N4001]

   $ controlled interface
      (I) A mechanism that facilitates the adjudication of the different
      security policies of interconnected systems. (See: domain, guard.)

   $ controlled security mode
      (D) /U.S. DoD/ A mode of system operation wherein (a) two or more
      security levels of information are allowed to be handled
      concurrently within the same system when some users having access
      to the system have neither a security clearance nor need-to-know
      for some of the data handled by the system, but (b) separation of
      the users and the classified material on the basis, respectively,
      of clearance and classification level are not dependent only on
      operating system control (like they are in multilevel security
      mode). (See: /system operation/ under "mode", protection level.)

      Deprecated Term: IDOCs SHOULD NOT use this term. It was defined in
      a U.S. Government policy regarding system accreditation and was
      subsumed by "partitioned security mode" in a later policy. Both
      terms were dropped in still later policies.

      Tutorial: Controlled mode was intended to encourage ingenuity in
      meeting data confidentiality requirements in ways less restrictive
      than "dedicated security mode" and "system-high security mode",
      but at a level of risk lower than that generally associated with
      true "multilevel security mode". This was intended to be
      accomplished by implementation of explicit augmenting measures to
      reduce or remove a substantial measure of system software
      vulnerability together with specific limitation of the security
      clearance levels of users having concurrent access to the system.

   $ controlling authority
      (O) /U.S. Government/ "Official responsible for directing the
      operation of a cryptonet and for managing the operational use and
      control of keying material assigned to the cryptonet." [C4009,
      N4006]

   $ cookie
      1. (I) /HTTP/ Data exchanged between an HTTP server and a browser
      (a client of the server) to store state information on the client
      side and retrieve it later for server use.

      Tutorial: An HTTP server, when sending data to a client, may send
      along a cookie, which the client retains after the HTTP connection
      closes. A server can use this mechanism to maintain persistent
      client-side state information for HTTP-based applications,
      retrieving the state information in later connections. A cookie
      may include a description of the range of URLs for which the state
      is valid. Future requests made by the client in that range will
      also send the current value of the cookie to the server. Cookies
      can be used to generate profiles of web usage habits, and thus may
      infringe on personal privacy.

      2. (I) /IPsec/ Data objects exchanged by ISAKMP to prevent certain
      denial-of-service attacks during the establishment of a security
      association.

      3. (D) /access control/ Synonym for "capability token" or
      "ticket".

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 3; that would duplicate the meaning of better-
      established terms and mix concepts in a potentially misleading
      way.

   $ Coordinated Universal Time (UTC)
      (N) UTC is derived from International Atomic Time (TAI) by adding
      a number of leap seconds. The International Bureau of Weights and
      Measures computes TAI once each month by averaging data from many
      laboratories. (See: GeneralizedTime, UTCTime.)

   $ correction
      (I) /security/ A system change made to eliminate or reduce the
      risk of reoccurrence of a security violation or threat
      consequence. (See: secondary definition under "security".)

   $ correctness
      (I) "The property of a system that is guaranteed as the result of
      formal verification activities." [Huff] (See: correctness proof,
      verification.)

   $ correctness integrity
      (I) The property that the information represented by data is
      accurate and consistent. (Compare: data integrity, source
      integrity.)

      Tutorial: IDOCs SHOULD NOT use this term without providing a
      definition; the term is neither well-known nor precisely defined.
      Data integrity refers to the constancy of data values, and source
      integrity refers to confidence in data values. However,

      correctness integrity refers to confidence in the underlying
      information that data values represent, and this property is
      closely related to issues of accountability and error handling.

   $ correctness proof
      (I) A mathematical proof of consistency between a specification
      for system security and the implementation of that specification.
      (See: correctness, formal specification.)

   $ corruption
      (I) A type of threat action that undesirably alters system
      operation by adversely modifying system functions or data. (See:
      disruption.)

      Usage: This type of threat action includes the following subtypes:
      -  "Tampering": /corruption/ Deliberately altering a system's
         logic, data, or control information to interrupt or prevent
         correct operation of system functions. (See: misuse, main entry
         for "tampering".)
      -  "Malicious logic": /corruption/ Any hardware, firmware, or
         software (e.g., a computer virus) intentionally introduced into
         a system to modify system functions or data. (See:
         incapacitation, main entry for "malicious logic", masquerade,
         misuse.)
      -  "Human error": /corruption/ Human action or inaction that
         unintentionally results in the alteration of system functions
         or data.
      -  "Hardware or software error": /corruption/ Error that results
         in the alteration of system functions or data.
      -  "Natural disaster": /corruption/ Any "act of God" (e.g., power
         surge caused by lightning) that alters system functions or
         data. [FP031 Section 2]

   $ counter
      1. (N) /noun/ See: counter mode.

      2. (I) /verb/ See: countermeasure.

   $ counter-countermeasure
      (I) An action, device, procedure, or technique used by an attacker
      to offset a defensive countermeasure.

      Tutorial: For every countermeasure devised to protect computers
      and networks, some cracker probably will be able to devise a
      counter-countermeasure. Thus, systems must use "defense in depth".

   $ counter mode (CTR)
      (N) A block cipher mode that enhances ECB mode by ensuring that
      each encrypted block is different from every other block encrypted
      under the same key. [SP38A] (See: block cipher.)

      Tutorial: This mode operates by first encrypting a generated
      sequence of blocks, called "counters", that are separate from the
      input sequence of plaintext blocks which the mode is intended to
      protect. The resulting sequence of encrypted counters is
      exclusive-ORed with the sequence of plaintext blocks to produce
      the final ciphertext output blocks. The sequence of counters must
      have the property that each counter is different from every other
      counter for all of the plain text that is encrypted under the same
      key.

   $ Counter with Cipher Block Chaining-Message Authentication Code
      (CCM)
      (N) A block cipher mode [SP38C] that provides both data
      confidentiality and data origin authentication, by combining the
      techniques of CTR and a CBC-based message authentication code.
      (See: block cipher.)

   $ countermeasure
      (I) An action, device, procedure, or technique that meets or
      opposes (i.e., counters) a threat, a vulnerability, or an attack
      by eliminating or preventing it, by minimizing the harm it can
      cause, or by discovering and reporting it so that corrective
      action can be taken.

      Tutorial: In an Internet protocol, a countermeasure may take the
      form of a protocol feature, a component function, or a usage
      constraint.

   $ country code
      (I) An identifier that is defined for a nation by ISO. [I3166]

      Tutorial: For each nation, ISO Standard 3166 defines a unique two-
      character alphabetic code, a unique three-character alphabetic
      code, and a three-digit code. Among many uses of these codes, the
      two-character codes are used as top-level domain names.

   $ Courtney's laws
      (N) Principles for managing system security that were stated by
      Robert H. Courtney, Jr.

      Tutorial: Bill Murray codified Courtney's laws as follows: [Murr]
      -  Courtney's first law: You cannot say anything interesting
         (i.e., significant) about the security of a system except in
         the context of a particular application and environment.
      -  Courtney's second law: Never spend more money eliminating a
         security exposure than tolerating it will cost you. (See:
         acceptable risk, risk analysis.)
         -- First corollary: Perfect security has infinite cost.
         -- Second corollary: There is no such thing as zero risk.
      -  Courtney's third law: There are no technical solutions to
         management problems, but there are management solutions to
         technical problems.

   $ covert action
      (I) An operation that is planned and executed in a way that
      conceals the identity of the operator.

   $ covert channel
      1. (I) An unintended or unauthorized intra-system channel that
      enables two cooperating entities to transfer information in a way
      that violates the system's security policy but does not exceed the
      entities' access authorizations. (See: covert storage channel,
      covert timing channel, out-of-band, tunnel.)

      2. (O) "A communications channel that allows two cooperating
      processes to transfer information in a manner that violates the
      system's security policy." [NCS04]

      Tutorial: The cooperating entities can be either two insiders or
      an insider and an outsider. Of course, an outsider has no access
      authorization at all. A covert channel is a system feature that
      the system architects neither designed nor intended for
      information transfer.

   $ covert storage channel
      (I) A system feature that enables one system entity to signal
      information to another entity by directly or indirectly writing a
      storage location that is later directly or indirectly read by the
      second entity. (See: covert channel.)

   $ covert timing channel
      (I) A system feature that enables one system entity to signal
      information to another by modulating its own use of a system
      resource in such a way as to affect system response time observed
      by the second entity. (See: covert channel.)

   $ CPS
      (I) See: certification practice statement.

   $ cracker
      (I) Someone who tries to break the security of, and gain
      unauthorized access to, someone else's system, often with
      malicious intent. (See: adversary, intruder, packet monkey, script
      kiddy. Compare: hacker.)

      Usage: Was sometimes spelled "kracker". [NCSSG]

   $ CRAM
      (I) See: Challenge-Response Authentication Mechanism.

   $ CRC
      (I) See: cyclic redundancy check.

   $ credential
      1. (I) /authentication/ "identifier credential": A data object
      that is a portable representation of the association between an
      identifier and a unit of authentication information, and that can
      be presented for use in verifying an identity claimed by an entity
      that attempts to access a system. Example: X.509 public-key
      certificate. (See: anonymous credential.)

      2. (I) /access control/ "authorization credential": A data object
      that is a portable representation of the association between an
      identifier and one or more access authorizations, and that can be
      presented for use in verifying those authorizations for an entity
      that attempts such access. Example: X.509 attribute certificate.
      (See: capability token, ticket.)

      3. (D) /OSIRM/ "Data that is transferred to establish the claimed
      identity of an entity." [I7498-2]

      Deprecated Definition: IDOCs SHOULD NOT use the term with
      definition 3. As explained in the tutorial below, an
      authentication process can involve the transfer of multiple data
      objects, and not all of those are credentials.

      4. (D) /U.S. Government/ "An object that is verified when
      presented to the verifier in an authentication transaction."
      [M0404]

      Deprecated Definition: IDOCs SHOULD NOT use the term with
      definition 4; it mixes concepts in a potentially misleading way.
      For example, in an authentication process, it is the identity that
      is "verified", not the credential; the credential is "validated".
      (See: validate vs. verify.)

      Tutorial: In general English, "credentials" are evidence or
      testimonials that (a) support a claim of identity or authorization
      and (b) usually are intended to be used more than once (i.e., a
      credential's life is long compared to the time needed for one
      use). Some examples are a policeman's badge, an automobile
      driver's license, and a national passport. An authentication or
      access control process that uses a badge, license, or passport is
      outwardly simple: the holder just shows the thing.

      The problem with adopting this term in Internet security is that
      an automated process for authentication or access control usually
      requires multiple steps using multiple data objects, and it might
      not be immediately obvious which of those objects should get the
      name "credential".

      For example, if the verification step in a user authentication
      process employs public-key technology, then the process involves
      at least three data items: (a) the user's private key, (b) a
      signed value -- signed with that private key and passed to the
      system, perhaps in response to a challenge from the system -- and
      (c) the user's public-key certificate, which is validated by the
      system and provides the public key needed to verify the signature.
      -  Private key: The private key is *not* a credential, because it
         is never transferred or presented. Instead, the private key is
         "authentication information", which is associated with the
         user's identifier for a specified period of time and can be
         used in multiple authentications during that time.
      -  Signed value: The signed value is *not* a credential; the
         signed value is only ephemeral, not long lasting. The OSIRM
         definition could be interpreted to call the signed value a
         credential, but that would conflict with general English.
      -  Certificate: The user's certificate *is* a credential. It can
         be "transferred" or "presented" to any person or process that
         needs it at any time. A public-key certificate may be used as
         an "identity credential", and an attribute certificate may be
         used as an "authorization credential".

   $ critical
      1. (I) /system resource/ A condition of a system resource such
      that denial of access to, or lack of availability of, that
      resource would jeopardize a system user's ability to perform a
      primary function or would result in other serious consequences,
      such as human injury or loss of life. (See: availability,
      precedence. Compare: sensitive.)

      2. (N) /extension/ An indication that an application is not
      permitted to ignore an extension. [X509]

      Tutorial: Each extension of an X.509 certificate or CRL is flagged
      as either "critical" or "non-critical". In a certificate, if a
      computer program does not recognize an extension's type (i.e.,
      does not implement its semantics), then if the extension is
      critical, the program is required to treat the certificate as
      invalid; but if the extension is non-critical, the program is
      permitted to ignore the extension.

      In a CRL, if a program does not recognize a critical extension
      that is associated with a specific certificate, the program is
      required to assume that the listed certificate has been revoked
      and is no longer valid, and then take whatever action is required
      by local policy.

      When a program does not recognize a critical extension that is
      associated with the CRL as a whole, the program is required to
      assume that all listed certificates have been revoked and are no
      longer valid. However, since failing to process the extension may
      mean that the list has not been completed, the program cannot
      assume that other certificates are valid, and the program needs to
      take whatever action is therefore required by local policy.

   $ critical information infrastructure
      (I) Those systems that are so vital to a nation that their
      incapacity or destruction would have a debilitating effect on
      national security, the economy, or public health and safety.

   $ CRL
      (I) See: certificate revocation list.

   $ CRL distribution point
      (I) See: distribution point.

   $ CRL extension
      (I) See: extension.

   $ cross-certificate
      (I) A public-key certificate issued by a CA in one PKI to a CA in
      another PKI. (See: cross-certification.)

   $ cross-certification
      (I) The act or process by which a CA in one PKI issues a public-
      key certificate to a CA in another PKI. [X509] (See: bridge CA.)

      Tutorial: X.509 says that a CA (say, CA1) may issue a "cross-
      certificate" in which the subject is another CA (say, CA2). X.509
      calls CA2 the "subject CA" and calls CA1 an "intermediate CA", but

      this Glossary deprecates those terms. (See: intermediate CA,
      subject CA).

      Cross-certification of CA2 by CA1 appears similar to certification
      of a subordinate CA by a superior CA, but cross-certification
      involves a different concept. The "subordinate CA" concept applies
      when both CAs are in the same PKI, i.e., when either (a) CA1 and
      CA2 are under the same root or (b) CA1 is itself a root. The
      "cross-certification" concept applies in other cases:

      First, cross-certification applies when two CAs are in different
      PKIs, i.e., when CA1 and CA2 are under different roots, or perhaps
      are both roots themselves. Issuing the cross-certificate enables
      end entities certified under CA1 in PK1 to construct the
      certification paths needed to validate the certificates of end
      entities certified under CA2 in PKI2. Sometimes, a pair of cross-
      certificates is issued -- by CA1 to CA2, and by CA2 to CA1 -- so
      that an end entity in either PKI can validate certificates issued
      in the other PKI.

      Second, X.509 says that two CAs in some complex, multi-CA PKI can
      cross-certify one another to shorten the certification paths
      constructed by end entities. Whether or not a CA may perform this
      or any other form of cross-certification, and how such
      certificates may be used by end entities, should be addressed by
      the local certificate policy and CPS.

   $ cross-domain solution
      1. (D) Synonym for "guard".

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "guard"; this term unnecessarily (and verbosely) duplicates the
      meaning of the long-established "guard".

      2. (O) /U.S. Government/ A process or subsystem that provides a
      capability (which could be either manual or automated) to access
      two or more differing security domains in a system, or to transfer
      information between such domains. (See: domain, guard.)

   $ cryptanalysis
      1. (I) The mathematical science that deals with analysis of a
      cryptographic system to gain knowledge needed to break or
      circumvent the protection that the system is designed to provide.
      (See: cryptology, secondary definition under "intrusion".)

      2. (O) "The analysis of a cryptographic system and/or its inputs
      and outputs to derive confidential variables and/or sensitive data
      including cleartext." [I7498-2]

      Tutorial: Definition 2 states the traditional goal of
      cryptanalysis, i.e., convert cipher text to plain text (which
      usually is clear text) without knowing the key; but that
      definition applies only to encryption systems. Today, the term is
      used with reference to all kinds of cryptographic algorithms and
      key management, and definition 1 reflects that. In all cases,
      however, a cryptanalyst tries to uncover or reproduce someone
      else's sensitive data, such as clear text, a key, or an algorithm.
      The basic cryptanalytic attacks on encryption systems are
      ciphertext-only, known-plaintext, chosen-plaintext, and chosen-
      ciphertext; and these generalize to the other kinds of
      cryptography.

   $ crypto, CRYPTO
      1. (N) A prefix ("crypto-") that means "cryptographic".

      Usage: IDOCs MAY use this prefix when it is part of a term listed
      in this Glossary. Otherwise, IDOCs SHOULD NOT use this prefix;
      instead, use the unabbreviated adjective, "cryptographic".

      2. (D) In lower case, "crypto" is an abbreviation for the
      adjective "cryptographic", or for the nouns "cryptography" or
      "cryptographic component".

      Deprecated Abbreviation: IDOCs SHOULD NOT use this abbreviation
      because it could easily be misunderstood in some technical sense.

      3. (O) /U.S. Government/ In upper case, "CRYPTO" is a marking or
      designator that identifies "COMSEC keying material used to secure
      or authenticate telecommunications carrying classified or
      sensitive U.S. Government or U.S. Government-derived information."
      [C4009] (See: security label, security marking.)

   $ cryptographic
      (I) An adjective that refers to cryptography.

   $ cryptographic algorithm
      (I) An algorithm that uses the science of cryptography, including
      (a) encryption algorithms, (b) cryptographic hash algorithms, (c)
      digital signature algorithms, and (d) key-agreement algorithms.

   $ cryptographic application programming interface (CAPI)
      (I) The source code formats and procedures through which an
      application program accesses cryptographic services, which are
      defined abstractly compared to their actual implementation.
      Example, see: PKCS #11, [R2628].

   $ cryptographic association
      (I) A security association that involves the use of cryptography
      to provide security services for data exchanged by the associated
      entities. (See: ISAKMP.)

   $ cryptographic boundary
      (I) See: secondary definition under "cryptographic module".

   $ cryptographic card
      (I) A cryptographic token in the form of a smart card or a PC
      card.

   $ cryptographic component
      (I) A generic term for any system component that involves
      cryptography. (See: cryptographic module.)

   $ cryptographic hash
      (I) See: secondary definition under "hash function".

   $ cryptographic ignition key (CIK)
      1. (N) A physical (usually electronic) token used to store,
      transport, and protect cryptographic keys and activation data.
      (Compare: dongle, fill device.)

      Tutorial: A key-encrypting key could be divided (see: split key)
      between a CIK and a cryptographic module, so that it would be
      necessary to combine the two to regenerate the key, use it to
      decrypt other keys and data contained in the module, and thus
      activate the module.

      2. (O) "Device or electronic key used to unlock the secure mode of
      cryptographic equipment." [C4009] Usage: Abbreviated as "crypto-
      ignition key".

   $ cryptographic key
      (I) See: key. Usage: Usually shortened to just "key".

   $ Cryptographic Message Syntax (CMS)
      (I) An encapsulation syntax (RFC 3852) for digital signatures,
      hashes, and encryption of arbitrary messages.

      Tutorial: CMS derives from PKCS #7. CMS values are specified with
      ASN.1 and use BER encoding. The syntax permits multiple
      encapsulation with nesting, permits arbitrary attributes to be
      signed along with message content, and supports a variety of
      architectures for digital certificate-based key management.

   $ cryptographic module
      (I) A set of hardware, software, firmware, or some combination
      thereof that implements cryptographic logic or processes,
      including cryptographic algorithms, and is contained within the
      module's "cryptographic boundary", which is an explicitly defined
      contiguous perimeter that establishes the physical bounds of the
      module. [FP140]

   $ cryptographic system
      1. (I) A set of cryptographic algorithms together with the key
      management processes that support use of the algorithms in some
      application context.

      Usage: IDOCs SHOULD use definition 1 because it covers a wider
      range of algorithms than definition 2.

      2. (O) "A collection of transformations from plain text into
      cipher text and vice versa [which would exclude digital signature,
      cryptographic hash, and key-agreement algorithms], the particular
      transformation(s) to be used being selected by keys. The
      transformations are normally defined by a mathematical algorithm."
      [X509]

   $ cryptographic token
      1. (I) A portable, user-controlled, physical device (e.g., smart
      card or PCMCIA card) used to store cryptographic information and
      possibly also perform cryptographic functions. (See: cryptographic
      card, token.)

      Tutorial: A smart token might implement some set of cryptographic
      algorithms and might incorporate related key management functions,
      such as a random number generator. A smart cryptographic token may
      contain a cryptographic module or may not be explicitly designed
      that way.

   $ cryptography
      1. (I) The mathematical science that deals with transforming data
      to render its meaning unintelligible (i.e., to hide its semantic
      content), prevent its undetected alteration, or prevent its
      unauthorized use. If the transformation is reversible,
      cryptography also deals with restoring encrypted data to
      intelligible form. (See: cryptology, steganography.)

      2. (O) "The discipline which embodies principles, means, and
      methods for the transformation of data in order to hide its
      information content, prevent its undetected modification and/or
      prevent its unauthorized use.... Cryptography determines the
      methods used in encipherment and decipherment." [I7498-2]

      Tutorial: Comprehensive coverage of applied cryptographic
      protocols and algorithms is provided by Schneier [Schn].
      Businesses and governments use cryptography to make data
      incomprehensible to outsiders; to make data incomprehensible to
      both outsiders and insiders, the data is sent to lawyers for a
      rewrite.

   $ Cryptoki
      (N) A CAPI defined in PKCS #11. Pronunciation: "CRYPTO-key".
      Derivation: Abbreviation of "cryptographic token interface".

   $ cryptology
      (I) The science of secret communication, which includes both
      cryptography and cryptanalysis.

      Tutorial: Sometimes the term is used more broadly to denote
      activity that includes both rendering signals secure (see: signal
      security) and extracting information from signals (see: signal
      intelligence) [Kahn].

   $ cryptonet
      (I) A network (i.e., a communicating set) of system entities that
      share a secret cryptographic key for a symmetric algorithm. (See:
      controlling authority.)

      (O) "Stations holding a common key." [C4009]

   $ cryptoperiod
      (I) The time span during which a particular key value is
      authorized to be used in a cryptographic system. (See: key
      management.)

      Usage: This term is long-established in COMPUSEC usage. In the
      context of certificates and public keys, "key lifetime" and
      "validity period" are often used instead.

      Tutorial: A cryptoperiod is usually stated in terms of calendar or
      clock time, but sometimes is stated in terms of the maximum amount
      of data permitted to be processed by a cryptographic algorithm
      using the key. Specifying a cryptoperiod involves a tradeoff
      between the cost of rekeying and the risk of successful
      cryptoanalysis.

   $ cryptosystem
      (I) Contraction of "cryptographic system".

   $ cryptovariable
      (D) Synonym for "key".

      Deprecated Usage: In contemporary COMSEC usage, the term "key" has
      replaced the term "cryptovariable".

   $ CSIRT
      (I) See: computer security incident response team.

   $ CSOR
      (N) See: Computer Security Objects Register.

   $ CTAK
      (D) See: ciphertext auto-key.

   $ CTR
      (N) See: counter mode.

   $ cut-and-paste attack
      (I) An active attack on the data integrity of cipher text,
      effected by replacing sections of cipher text with other cipher
      text, such that the result appears to decrypt correctly but
      actually decrypts to plain text that is forged to the satisfaction
      of the attacker.

   $ cyclic redundancy check (CRC)
      (I) A type of checksum algorithm that is not a cryptographic hash
      but is used to implement data integrity service where accidental
      changes to data are expected. Sometimes called "cyclic redundancy
      code".

   $ DAC
      (N) See: Data Authentication Code, discretionary access control.

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because this abbreviation is ambiguous.

   $ daemon
      (I) A computer program that is not invoked explicitly but waits
      until a specified condition occurs, and then runs with no
      associated user (principal), usually for an administrative
      purpose. (See: zombie.)

   $ dangling threat
      (O) A threat to a system for which there is no corresponding
      vulnerability and, therefore, no implied risk.

   $ dangling vulnerability
      (O) A vulnerability of a system for which there is no
      corresponding threat and, therefore, no implied risk.

   $ DASS
      (I) See: Distributed Authentication Security Service.

   $ data
      (I) Information in a specific representation, usually as a
      sequence of symbols that have meaning.

      Usage: Refers to both (a) representations that can be recognized,
      processed, or produced by a computer or other type of machine, and
      (b) representations that can be handled by a human.

   $ Data Authentication Algorithm, data authentication algorithm
      1. (N) /capitalized/ The ANSI standard for a keyed hash function
      that is equivalent to DES cipher block chaining with IV = 0.
      [A9009]

      2. (D) /not capitalized/ Synonym for some kind of "checksum".

      Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form "data
      authentication algorithm" as a synonym for any kind of checksum,
      regardless of whether or not the checksum is based on a hash.
      Instead, use "checksum", "Data Authentication Code", "error
      detection code", "hash", "keyed hash", "Message Authentication
      Code", "protected checksum", or some other specific term,
      depending on what is meant.

      The uncapitalized term can be confused with the Data
      Authentication Code and also mixes concepts in a potentially
      misleading way. The word "authentication" is misleading because
      the checksum may be used to perform a data integrity function
      rather than a data origin authentication function.

   $ Data Authentication Code, data authentication code
      1. (N) /capitalized/ A specific U.S. Government standard [FP113]
      for a checksum that is computed by the Data Authentication
      Algorithm. Usage: a.k.a. Message Authentication Code [A9009].)
      (See: DAC.)

      2. (D) /not capitalized/ Synonym for some kind of "checksum".

      Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form "data
      authentication code" as a synonym for any kind of checksum,
      regardless of whether or not the checksum is based on the Data
      Authentication Algorithm. The uncapitalized term can be confused
      with the Data Authentication Code and also mixes concepts in a
      potentially misleading way (see: authentication code).

   $ data compromise
      1. (I) A security incident in which information is exposed to
      potential unauthorized access, such that unauthorized disclosure,
      alteration, or use of the information might have occurred.
      (Compare: security compromise, security incident.)

      2. (O) /U.S. DoD/ A "compromise" is a "communication or physical
      transfer of information to an unauthorized recipient." [DoD5]

      3. (O) /U.S. Government/ "Type of [security] incident where
      information is disclosed to unauthorized individuals or a
      violation of the security policy of a system in which unauthorized
      intentional or unintentional disclosure, modification,
      destruction, or loss of an object may have occurred." [C4009]

   $ data confidentiality
      1. (I) The property that data is not disclosed to system entities
      unless they have been authorized to know the data. (See: Bell-
      LaPadula model, classification, data confidentiality service,
      secret. Compare: privacy.)

      2. (D) "The property that information is not made available or
      disclosed to unauthorized individuals, entities, or processes
      [i.e., to any unauthorized system entity]." [I7498-2].

      Deprecated Definition: The phrase "made available" might be
      interpreted to mean that the data could be altered, and that would
      confuse this term with the concept of "data integrity".

   $ data confidentiality service
      (I) A security service that protects data against unauthorized
      disclosure. (See: access control, data confidentiality, datagram
      confidentiality service, flow control, inference control.)

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      "privacy", which is a different concept.

   $ Data Encryption Algorithm (DEA)
      (N) A symmetric block cipher, defined in the U.S. Government's
      DES. DEA uses a 64-bit key, of which 56 bits are independently
      chosen and 8 are parity bits, and maps a 64-bit block into another
      64-bit block. [FP046] (See: AES, symmetric cryptography.)

      Usage: This algorithm is usually referred to as "DES". The
      algorithm has also been adopted in standards outside the
      Government (e.g., [A3092]).

   $ data encryption key (DEK)
      (I) A cryptographic key that is used to encipher application data.
      (Compare: key-encrypting key.)

   $ Data Encryption Standard (DES)
      (N) A U.S. Government standard [FP046] that specifies the DEA and
      states policy for using the algorithm to protect unclassified,
      sensitive data. (See: AES.)

   $ data integrity
      1. (I) The property that data has not been changed, destroyed, or
      lost in an unauthorized or accidental manner. (See: data integrity
      service. Compare: correctness integrity, source integrity.)

      2. (O) "The property that information has not been modified or
      destroyed in an unauthorized manner." [I7498-2]

      Usage: Deals with (a) constancy of and confidence in data values,
      and not with either (b) information that the values represent
      (see: correctness integrity) or (c) the trustworthiness of the
      source of the values (see: source integrity).

   $ data integrity service
      (I) A security service that protects against unauthorized changes
      to data, including both intentional change or destruction and
      accidental change or loss, by ensuring that changes to data are
      detectable. (See: data integrity, checksum, datagram integrity
      service.)

      Tutorial: A data integrity service can only detect a change and
      report it to an appropriate system entity; changes cannot be
      prevented unless the system is perfect (error-free) and no
      malicious user has access. However, a system that offers data
      integrity service might also attempt to correct and recover from
      changes.

      The ability of this service to detect changes is limited by the
      technology of the mechanisms used to implement the service. For
      example, if the mechanism were a one-bit parity check across each
      entire SDU, then changes to an odd number of bits in an SDU would
      be detected, but changes to an even number of bits would not.

      Relationship between data integrity service and authentication
      services: Although data integrity service is defined separately
      from data origin authentication service and peer entity
      authentication service, it is closely related to them.
      Authentication services depend, by definition, on companion data
      integrity services. Data origin authentication service provides

      verification that the identity of the original source of a
      received data unit is as claimed; there can be no such
      verification if the data unit has been altered. Peer entity
      authentication service provides verification that the identity of
      a peer entity in a current association is as claimed; there can be
      no such verification if the claimed identity has been altered.

   $ data origin authentication
      (I) "The corroboration that the source of data received is as
      claimed." [I7498-2] (See: authentication.)

   $ data origin authentication service
      (I) A security service that verifies the identity of a system
      entity that is claimed to be the original source of received data.
      (See: authentication, authentication service.)

      Tutorial: This service is provided to any system entity that
      receives or holds the data. Unlike peer entity authentication
      service, this service is independent of any association between
      the originator and the recipient, and the data in question may
      have originated at any time in the past.

      A digital signature mechanism can be used to provide this service,
      because someone who does not know the private key cannot forge the
      correct signature. However, by using the signer's public key,
      anyone can verify the origin of correctly signed data.

      This service is usually bundled with connectionless data integrity
      service. (See: "relationship between data integrity service and
      authentication services" under "data integrity service".

   $ data owner
      (N) The organization that has the final statutory and operational
      authority for specified information.

   $ data privacy
      (D) Synonym for "data confidentiality".

      Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
      in a potentially misleading way. Instead, use either "data
      confidentiality" or "privacy" or both, depending on what is meant.

   $ data recovery
      1. (I) /cryptanalysis/ A process for learning, from some cipher
      text, the plain text that was previously encrypted to produce the
      cipher text. (See: recovery.)

      2. (I) /system integrity/ The process of restoring information
      following damage or destruction.

   $ data security
      (I) The protection of data from disclosure, alteration,
      destruction, or loss that either is accidental or is intentional
      but unauthorized.

      Tutorial: Both data confidentiality service and data integrity
      service are needed to achieve data security.

   $ datagram
      (I) "A self-contained, independent entity of data [i.e., a packet]
      carrying sufficient information to be routed from the source
      [computer] to the destination computer without reliance on earlier
      exchanges between this source and destination computer and the
      transporting network." [R1983] Example: A PDU of IP.

   $ datagram confidentiality service
      (I) A data confidentiality service that preserves the
      confidentiality of data in a single, independent, packet; i.e.,
      the service applies to datagrams one-at-a-time. Example: ESP.
      (See: data confidentiality.)

      Usage: When a protocol is said to provide data confidentiality
      service, this is usually understood to mean that only the SDU is
      protected in each packet. IDOCs that use the term to mean that the
      entire PDU is protected should include a highlighted definition.

      Tutorial: This basic form of network confidentiality service
      suffices for protecting the data in a stream of packets in both
      connectionless and connection-oriented protocols. Except perhaps
      for traffic flow confidentiality, nothing further is needed to
      protect the confidentiality of data carried by a packet stream.
      The OSIRM distinguishes between connection confidentiality and
      connectionless confidentiality. The IPS need not make that
      distinction, because those services are just instances of the same
      service (i.e., datagram confidentiality) being offered in two
      different protocol contexts. (For data integrity service, however,
      additional effort is needed to protect a stream, and the IPS does
      need to distinguish between "datagram integrity service" and
      "stream integrity service".)

   $ datagram integrity service
      (I) A data integrity service that preserves the integrity of data
      in a single, independent, packet; i.e., the service applies to
      datagrams one-at-a-time. (See: data integrity. Compare: stream
      integrity service.)

      Tutorial: The ability to provide appropriate data integrity is
      important in many Internet security situations, and so there are
      different kinds of data integrity services suited to different
      applications. This service is the simplest kind; it is suitable
      for connectionless data transfers.

      Datagram integrity service usually is designed only to attempt to
      detect changes to the SDU in each packet, but it might also
      attempt to detect changes to some or all of the PCI in each packet
      (see: selective field integrity). In contrast to this simple,
      one-at-a-time service, some security situations demand a more
      complex service that also attempts to detect deleted, inserted, or
      reordered datagrams within a stream of datagrams (see: stream
      integrity service).

   $ DEA
      (N) See: Data Encryption Algorithm.

   $ deception
      (I) A circumstance or event that may result in an authorized
      entity receiving false data and believing it to be true. (See:
      authentication.)

      Tutorial: This is a type of threat consequence, and it can be
      caused by the following types of threat actions: masquerade,
      falsification, and repudiation.

   $ decipher
      (D) Synonym for "decrypt".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "decrypt". However, see usage note under "encryption".

   $ decipherment
      (D) Synonym for "decryption".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "decryption". However, see the Usage note under "encryption".

   $ declassification
      (I) An authorized process by which information is declassified.
      (Compare: classification.)

   $ declassify
      (I) To officially remove the security level designation of a
      classified information item or information type, such that the
      information is no longer classified (i.e., becomes unclassified).
      (See: classified, classify, security level. Compare: downgrade.)

   $ decode
      1. (I) Convert encoded data back to its original form of
      representation. (Compare: decrypt.)

      2. (D) Synonym for "decrypt".

      Deprecated Definition: Encoding is not usually meant to conceal
      meaning. Therefore, IDOCs SHOULD NOT use this term as a synonym
      for "decrypt", because that would mix concepts in a potentially
      misleading way.

   $ decrypt
      (I) Cryptographically restore cipher text to the plaintext form it
      had before encryption.

   $ decryption
      (I) See: secondary definition under "encryption".

   $ dedicated security mode
      (I) A mode of system operation wherein all users having access to
      the system possess, for all data handled by the system, both (a)
      all necessary authorizations (i.e., security clearance and formal
      access approval) and (b) a need-to-know. (See: /system operation/
      under "mode", formal access approval, need to know, protection
      level, security clearance.)

      Usage: Usually abbreviated as "dedicated mode". This mode was
      defined in U.S. Government policy on system accreditation, but the
      term is also used outside the Government. In this mode, the system
      may handle either (a) a single classification level or category of
      information or (b) a range of levels and categories.

   $ default account
      (I) A system login account (usually accessed with a user
      identifier and password) that has been predefined in a
      manufactured system to permit initial access when the system is
      first put into service. (See: harden.)

      Tutorial: A default account becomes a serious vulnerability if not
      properly administered. Sometimes, the default identifier and
      password are well-known because they are the same in each copy of
      the system. In any case, when a system is put into service, any
      default password should immediately be changed or the default
      account should be disabled.

   $ defense in depth
      (N) "The siting of mutually supporting defense positions designed
      to absorb and progressively weaken attack, prevent initial

      observations of the whole position by the enemy, and [enable] the
      commander to maneuver the reserve." [JP1]

      Tutorial: In information systems, defense in depth means
      constructing a system's security architecture with layered and
      complementary security mechanisms and countermeasures, so that if
      one security mechanism is defeated, one or more other mechanisms
      (which are "behind" or "beneath" the first mechanism) still
      provide protection.

      This architectural concept is appealing because it aligns with
      traditional warfare doctrine, which applies defense in depth to
      physical, geospatial structures; but applying the concept to
      logical, cyberspace structures of computer networks is more
      difficult. The concept assumes that networks have a spatial or
      topological representation. It also assumes that there can be
      implemented -- from the "outer perimeter" of a network, through
      its various "layers" of components, to its "center" (i.e., to the
      subscriber application systems supported by the network) -- a
      varied series of countermeasures that together provide adequate
      protection. However, it is more difficult to map the topology of
      networks and make certain that no path exists by which an attacker
      could bypass all defensive layers.

   $ Defense Information Infrastructure (DII)
      (O) /U.S. DoD/ The U.S. DoD's shared, interconnected system of
      computers, communications, data, applications, security, people,
      training, and support structures, serving information needs
      worldwide. (See: DISN.) Usage: Has evolved to be called the GIG.

      Tutorial: The DII connects mission support, command and control,
      and intelligence computers and users through voice, data, imagery,
      video, and multimedia services, and provides information
      processing and value-added services to subscribers over the DISN.
      Users' own data and application software are not considered part
      of the DII.

   $ Defense Information Systems Network (DISN)
      (O) /U.S. DoD/ The U.S. DoD's consolidated, worldwide, enterprise
      level telecommunications infrastructure that provides end-to-end
      information transfer for supporting military operations; a part of
      the DII. (Compare: GIG.)

   $ degauss
      1a. (N) Apply a magnetic field to permanently remove data from a
      magnetic storage medium, such as a tape or disk [NCS25]. (Compare:
      erase, purge, sanitize.)

      1b. (N) Reduce magnetic flux density to zero by applying a
      reversing magnetic field. (See: magnetic remanence.)

   $ degausser
      (N) An electrical device that can degauss magnetic storage media.

   $ DEK
      (I) See: data encryption key.

   $ delay
      (I) /packet/ See: secondary definition under "stream integrity
      service".

   $ deletion
      (I) /packet/ See: secondary definition under "stream integrity
      service".

   $ deliberate exposure
      (I) /threat action/ See: secondary definition under "exposure".

   $ delta CRL
      (I) A partial CRL that only contains entries for certificates that
      have been revoked since the issuance of a prior, base CRL [X509].
      This method can be used to partition CRLs that become too large
      and unwieldy. (Compare: CRL distribution point.)

   $ demilitarized zone (DMZ)
      (D) Synonym for "buffer zone".

      Deprecated Term: IDOCs SHOULD NOT use this term because it mixes
      concepts in a potentially misleading way. (See: Deprecated Usage
      under "Green Book".)

   $ denial of service
      (I) The prevention of authorized access to a system resource or
      the delaying of system operations and functions. (See:
      availability, critical, flooding.)

      Tutorial: A denial-of-service attack can prevent the normal
      conduct of business on the Internet. There are four types of
      solutions to this security problem:
      -  Awareness: Maintaining cognizance of security threats and
         vulnerabilities. (See: CERT.)
      -  Detection: Finding attacks on end systems and subnetworks.
         (See: intrusion detection.)
      -  Prevention: Following defensive practices on network-connected
         systems. (See: [R2827].)

      -  Response: Reacting effectively when attacks occur. (See: CSIRT,
         contingency plan.)

   $ DES
      (N) See: Data Encryption Standard.

   $ designated approving authority (DAA)
      (O) /U.S. Government/ Synonym for "accreditor".

   $ detection
      (I) See: secondary definition under "security".

   $ deterrence
      (I) See: secondary definition under "security".

   $ dictionary attack
      (I) An attack that uses a brute-force technique of successively
      trying all the words in some large, exhaustive list.

      Examples: Attack an authentication service by trying all possible
      passwords. Attack an encryption service by encrypting some known
      plaintext phrase with all possible keys so that the key for any
      given encrypted message containing that phrase may be obtained by
      lookup.

   $ Diffie-Hellman
   $ Diffie-Hellman-Merkle
      (N) A key-agreement algorithm published in 1976 by Whitfield
      Diffie and Martin Hellman [DH76, R2631].

      Usage: The algorithm is most often called "Diffie-Hellman".
      However, in the November 1978 issue of "IEEE Communications
      Magazine", Hellman wrote that the algorithm "is a public key
      distribution system, a concept developed by [Ralph C.] Merkle, and
      hence should be called 'Diffie-Hellman-Merkle' ... to recognize
      Merkle's equal contribution to the invention of public key
      cryptography."

      Tutorial: Diffie-Hellman-Merkle does key establishment, not
      encryption. However, the key that it produces may be used for
      encryption, for further key management operations, or for any
      other cryptography.

      The algorithm is described in [R2631] and [Schn]. In brief, Alice
      and Bob together pick large integers that satisfy certain
      mathematical conditions, and then use the integers to each
      separately compute a public-private key pair. They send each other
      their public key. Each person uses their own private key and the

      other person's public key to compute a key, k, that, because of
      the mathematics of the algorithm, is the same for each of them.
      Passive wiretapping cannot learn the shared k, because k is not
      transmitted, and neither are the private keys needed to compute k.

      The difficulty of breaking Diffie-Hellman-Merkle is considered to
      be equal to the difficulty of computing discrete logarithms modulo
      a large prime. However, without additional mechanisms to
      authenticate each party to the other, a protocol based on the
      algorithm may be vulnerable to a man-in-the-middle attack.

   $ digest
      See: message digest.

   $ digital certificate
      (I) A certificate document in the form of a digital data object (a
      data object used by a computer) to which is appended a computed
      digital signature value that depends on the data object. (See:
      attribute certificate, public-key certificate.)

      Deprecated Usage: IDOCs SHOULD NOT use this term to refer to a
      signed CRL or CKL. Although the recommended definition can be
      interpreted to include other signed items, the security community
      does not use the term with those meanings.

   $ digital certification
      (D) Synonym for "certification".

      Deprecated Definition: IDOCs SHOULD NOT use this definition unless
      the context is not sufficient to distinguish between digital
      certification and another kind of certification, in which case it
      would be better to use "public-key certification" or another
      phrase that indicates what is being certified.

   $ digital document
      (I) An electronic data object that represents information
      originally written in a non-electronic, non-magnetic medium
      (usually ink on paper) or is an analogue of a document of that
      type.

   $ digital envelope
      (I) A combination of (a) encrypted content data (of any kind)
      intended for a recipient and (b) the content encryption key in an
      encrypted form that has been prepared for the use of the
      recipient.

      Usage: In IDOCs, the term SHOULD be defined at the point of first
      use because, although the term is defined in PKCS #7 and used in
      S/MIME, it is not widely known.

      Tutorial: Digital enveloping is not simply a synonym for
      implementing data confidentiality with encryption; digital
      enveloping is a hybrid encryption scheme to "seal" a message or
      other data, by encrypting the data and sending both it and a
      protected form of the key to the intended recipient, so that no
      one other than the intended recipient can "open" the message. In
      PKCS #7, it means first encrypting the data using a symmetric
      encryption algorithm and a secret key, and then encrypting the
      secret key using an asymmetric encryption algorithm and the public
      key of the intended recipient. In S/MIME, additional methods are
      defined for encrypting the content encryption key.

   $ Digital ID(service mark)
      (D) Synonym for "digital certificate".

      Deprecated Term: IDOCs SHOULD NOT use this term. It is a service
      mark of a commercial firm, and it unnecessarily duplicates the
      meaning of a better-established term. (See: credential.)

   $ digital key
      (D) Synonym for an input parameter of a cryptographic algorithm or
      other process. (See: key.)

      Deprecated Usage: The adjective "digital" need not be used with
      "key" or "cryptographic key", unless the context is insufficient
      to distinguish the digital key from another kind of key, such as a
      metal key for a door lock.

   $ digital notary
      (I) An electronic functionary analogous to a notary public.
      Provides a trusted timestamp for a digital document, so that
      someone can later prove that the document existed at that point in
      time; verifies the signature(s) on a signed document before
      applying the stamp. (See: notarization.)

   $ digital signature
      1. (I) A value computed with a cryptographic algorithm and
      associated with a data object in such a way that any recipient of
      the data can use the signature to verify the data's origin and
      integrity. (See: data origin authentication service, data
      integrity service, signer. Compare: digitized signature,
      electronic signature.)

      2. (O) "Data appended to, or a cryptographic transformation of, a
      data unit that allows a recipient of the data unit to prove the
      source and integrity of the data unit and protect against forgery,
      e.g. by the recipient." [I7498-2]

      Tutorial: A digital signature should have these properties:
      -  Be capable of being verified. (See: validate vs. verify.)
      -  Be bound to the signed data object in such a way that if the
         data is changed, then when an attempt is made to verify the
         signature, it will be seen as not authentic. (In some schemes,
         the signature is appended to the signed object as stated by
         definition 2, but in other it, schemes is not.)
      -  Uniquely identify a system entity as being the signer.
      -  Be under the signer's sole control, so that it cannot be
         created by any other entity.

      To achieve these properties, the data object is first input to a
      hash function, and then the hash result is cryptographically
      transformed using a private key of the signer. The final resulting
      value is called the digital signature of the data object. The
      signature value is a protected checksum, because the properties of
      a cryptographic hash ensure that if the data object is changed,
      the digital signature will no longer match it. The digital
      signature is unforgeable because one cannot be certain of
      correctly creating or changing the signature without knowing the
      private key of the supposed signer.

      Some digital signature schemes use an asymmetric encryption
      algorithm (e.g., "RSA") to transform the hash result. Thus, when
      Alice needs to sign a message to send to Bob, she can use her
      private key to encrypt the hash result. Bob receives both the
      message and the digital signature. Bob can use Alice's public key
      to decrypt the signature, and then compare the plaintext result to
      the hash result that he computes by hashing the message himself.
      If the values are equal, Bob accepts the message because he is
      certain that it is from Alice and has arrived unchanged. If the
      values are not equal, Bob rejects the message because either the
      message or the signature was altered in transit.

      Other digital signature schemes (e.g., "DSS") transform the hash
      result with an algorithm (e.g., "DSA", "El Gamal") that cannot be
      directly used to encrypt data. Such a scheme creates a signature
      value from the hash and provides a way to verify the signature
      value, but does not provide a way to recover the hash result from
      the signature value. In some countries, such a scheme may improve
      exportability and avoid other legal constraints on usage. Alice
      sends the signature value to Bob along with both the message and
      its hash result. The algorithm enables Bob to use Alice's public

      signature key and the signature value to verify the hash result he
      receives. Then, as before, he compares that hash result she sent
      to the one that he computes by hashing the message himself.

   $ Digital Signature Algorithm (DSA)
      (N) An asymmetric cryptographic algorithm for a digital signature
      in the form of a pair of large numbers. The signature is computed
      using rules and parameters such that the identity of the signer
      and the integrity of the signed data can be verified. (See: DSS.)

   $ Digital Signature Standard (DSS)
      (N) The U.S. Government standard [FP186] that specifies the DSA.

   $ digital watermarking
      (I) Computing techniques for inseparably embedding unobtrusive
      marks or labels as bits in digital data -- text, graphics, images,
      video, or audio -- and for detecting or extracting the marks
      later.

      Tutorial: A "digital watermark", i.e., the set of embedded bits,
      is sometimes hidden, usually imperceptible, and always intended to
      be unobtrusive. Depending on the particular technique that is
      used, digital watermarking can assist in proving ownership,
      controlling duplication, tracing distribution, ensuring data
      integrity, and performing other functions to protect intellectual
      property rights. [ACM]

   $ digitized signature
      (D) Denotes various forms of digitized images of handwritten
      signatures. (Compare: digital signature).

      Deprecated Term: IDOCs SHOULD NOT use this term without including
      this definition. This term suggests careless use of "digital
      signature", which is the term standardized by [I7498-2]. (See:
      electronic signature.)

   $ DII
      (O) See: Defense Information Infrastructure.

   $ direct attack
      (I) See: secondary definition under "attack". (Compare: indirect
      attack.)

   $ directory, Directory
      1. (I) /not capitalized/ Refers generically to a database server
      or other system that stores and provides access to values of
      descriptive or operational data items that are associated with the
      components of a system. (Compare: repository.)

      2. (N) /capitalized/ Refers specifically to the X.500 Directory.
      (See: DN, X.500.)

   $ Directory Access Protocol (DAP)
      (N) An OSI protocol [X519] for communication between a Directory
      User Agent (a type of X.500 client) and a Directory System Agent
      (a type of X.500 server). (See: LDAP.)

   $ disaster plan
      (O) Synonym for "contingency plan".

      Deprecated Term: IDOCs SHOULD NOT use this term; instead, for
      consistency and neutrality of language, IDOCs SHOULD use
      "contingency plan".

   $ disclosure
      See: unauthorized disclosure. Compare: exposure.

   $ discretionary access control
      1a. (I) An access control service that (a) enforces a security
      policy based on the identity of system entities and the
      authorizations associated with the identities and (b) incorporates
      a concept of ownership in which access rights for a system
      resource may be granted and revoked by the entity that owns the
      resource. (See: access control list, DAC, identity-based security
      policy, mandatory access control.)

      Derivation: This service is termed "discretionary" because an
      entity can be granted access rights to a resource such that the
      entity can by its own volition enable other entities to access the
      resource.

      1b. (O) /formal model/ "A means of restricting access to objects
      based on the identity of subjects and/or groups to which they
      belong. The controls are discretionary in the sense that a subject
      with a certain access permission is capable of passing that
      permission (perhaps indirectly) on to any other subject." [DoD1]

   $ DISN
      (O) See: Defense Information Systems Network (DISN).

   $ disruption
      (I) A circumstance or event that interrupts or prevents the
      correct operation of system services and functions. (See:
      availability, critical, system integrity, threat consequence.)

      Tutorial: Disruption is a type of threat consequence; it can be
      caused by the following types of threat actions: incapacitation,
      corruption, and obstruction.

   $ Distinguished Encoding Rules (DER)
      (N) A subset of the Basic Encoding Rules that always provides only
      one way to encode any data structure defined by ASN.1. [X690].

      Tutorial: For a data structure defined abstractly in ASN.1, BER
      often provides for encoding the structure into an octet string in
      more than one way, so that two separate BER implementations can
      legitimately produce different octet strings for the same ASN.1
      definition. However, some applications require all encodings of a
      structure to be the same, so that encodings can be compared for
      equality. Therefore, DER is used in applications in which unique
      encoding is needed, such as when a digital signature is computed
      on a structure defined by ASN.1.

   $ distinguished name (DN)
      (N) An identifier that uniquely represents an object in the X.500
      Directory Information Tree (DIT) [X501]. (Compare: domain name,
      identity, naming authority.)

      Tutorial: A DN is a set of attribute values that identify the path
      leading from the base of the DIT to the object that is named. An
      X.509 public-key certificate or CRL contains a DN that identifies
      its issuer, and an X.509 attribute certificate contains a DN or
      other form of name that identifies its subject.

   $ distributed attack
      1a. (I) An attack that is implemented with distributed computing.
      (See: zombie.)

      1b. (I) An attack that deploys multiple threat agents.

   $ Distributed Authentication Security Service (DASS)
      (I) An experimental Internet protocol [R1507] that uses
      cryptographic mechanisms to provide strong, mutual authentication
      services in a distributed environment.

   $ distributed computing
      (I) A technique that disperses a single, logically related set of
      tasks among a group of geographically separate yet cooperating
      computers. (See: distributed attack.)

   $ distribution point
      (I) An X.500 Directory entry or other information source that is
      named in a v3 X.509 public-key certificate extension as a location
      from which to obtain a CRL that may list the certificate.

      Tutorial: A v3 X.509 public-key certificate may have a
      "cRLDistributionPoints" extension that names places to get CRLs on
      which the certificate might be listed. (See: certificate profile.)
      A CRL obtained from a distribution point may (a) cover either all
      reasons for which a certificate might be revoked or only some of
      the reasons, (b) be issued by either the authority that signed the
      certificate or some other authority, and (c) contain revocation
      entries for only a subset of the full set of certificates issued
      by one CA or (d) contain revocation entries for multiple CAs.

   $ DKIM
      (I) See: Domain Keys Identified Mail.

   $ DMZ
      (D) See: demilitarized zone.

   $ DN
      (N) See: distinguished name.

   $ DNS
      (I) See: Domain Name System.

   $ doctrine
      See: security doctrine.

   $ DoD
      (N) Department of Defense.

      Usage: To avoid international misunderstanding, IDOCs SHOULD use
      this abbreviation only with a national qualifier (e.g., U.S. DoD).

   $ DOI
      (I) See: Domain of Interpretation.

   $ domain
      1a. (I) /general security/ An environment or context that (a)
      includes a set of system resources and a set of system entities
      that have the right to access the resources and (b) usually is
      defined by a security policy, security model, or security
      architecture. (See: CA domain, domain of interpretation, security
      perimeter. Compare: COI, enclave.)

      Tutorial: A "controlled interface" or "guard" is required to
      transfer information between network domains that operate under
      different security policies.

      1b. (O) /security policy/ A set of users, their information
      objects, and a common security policy. [DoD6, SP33]

      1c. (O) /security policy/ A system or collection of systems that
      (a) belongs to a community of interest that implements a
      consistent security policy and (b) is administered by a single
      authority.

      2. (O) /COMPUSEC/ An operating state or mode of a set of computer
      hardware.

      Tutorial: Most computers have at least two hardware operating
      modes [Gass]:
      -  "Privileged" mode: a.k.a. "executive", "master", "system",
         "kernel", or "supervisor" mode. In this mode, software can
         execute all machine instructions and access all storage
         locations.
      -  "Unprivileged" mode: a.k.a. "user", "application", or "problem"
         mode. In this mode, software is restricted to a subset of the
         instructions and a subset of the storage locations.

      3. (O) "A distinct scope within which certain common
      characteristics are exhibited and common rules are observed."
      [CORBA]

      4. (O) /MISSI/ The domain of a MISSI CA is the set of MISSI users
      whose certificates are signed by the CA.

      5. (I) /Internet/ That part of the tree-structured name space of
      the DNS that is at or below the name that specifies the domain. A
      domain is a subdomain of another domain if it is contained within
      that domain. For example, D.C.B.A is a subdomain of C.B.A

6. (O) /OSI/ An administrative partition of a complex distributed
OSI system.

   $ Domain Keys Identified Mail (DKIM)
      (I) A protocol, which is being specified by the IETF working group
      of the same name, to provide data integrity and domain-level (see:
      DNS, domain name) data origin authentication for Internet mail
      messages. (Compare: PEM.)

      Tutorial: DKIM employs asymmetric cryptography to create a digital
      signature for an Internet email message's body and selected

      headers (see RFC 1822), and the signature is then carried in a
      header of the message. A recipient of the message can verify the
      signature and, thereby, authenticate the identity of the
      originating domain and the integrity of the signed content, by
      using a public key belonging to the domain. The key can be
      obtained from the DNS.

   $ domain name
      (I) The style of identifier that is defined for subtrees in the
      Internet DNS -- i.e., a sequence of case-insensitive ASCII labels
      separated by dots (e.g., "bbn.com") -- and also is used in other
      types of Internet identifiers, such as host names (e.g.,
      "rosslyn.bbn.com"), mailbox names (e.g., "rshirey@bbn.com") and
      URLs (e.g., "http://www.rosslyn.bbn.com/foo"). (See: domain.
      Compare: DN.)

      Tutorial: The name space of the DNS is a tree structure in which
      each node and leaf holds records describing a resource. Each node
      has a label. The domain name of a node is the list of labels on
      the path from the node to the root of the tree. The labels in a
      domain name are printed or read left to right, from the most
      specific (lowest, farthest from the root) to the least specific
      (highest, closest to the root), but the root's label is the null
      string. (See: country code.)

   $ Domain Name System (DNS)
      (I) The main Internet operations database, which is distributed
      over a collection of servers and used by client software for
      purposes such as (a) translating a domain name-style host name
      into an IP address (e.g., "rosslyn.bbn.com" translates to
      "192.1.7.10") and (b) locating a host that accepts mail for a
      given mailbox address. (RFC 1034) (See: domain name.)

      Tutorial: The DNS has three major components:
      -  Domain name space and resource records: Specifications for the
         tree-structured domain name space, and data associated with the
         names.
      -  Name servers: Programs that hold information about a subset of
         the tree's structure and data holdings, and also hold pointers
         to other name servers that can provide information from any
         part of the tree.
      -  Resolvers: Programs that extract information from name servers
         in response to client requests; typically, system routines
         directly accessible to user programs.

      Extensions to the DNS [R4033, R4034, R4035] support (a) key
      distribution for public keys needed for the DNS and for other
      protocols, (b) data origin authentication service and data

      integrity service for resource records, (c) data origin
      authentication service for transactions between resolvers and
      servers, and (d) access control of records.

   $ domain of interpretation (DOI)
      (I) /IPsec/ A DOI for ISAKMP or IKE defines payload formats,
      exchange types, and conventions for naming security-relevant
      information such as security policies or cryptographic algorithms
      and modes. Example: See [R2407].

      Derivation: The DOI concept is based on work by the TSIG's CIPSO
      Working Group.

   $ dominate
      (I) Security level A is said to "dominate" security level B if the
      (hierarchical) classification level of A is greater (higher) than
      or equal to that of B, and A's (nonhierarchical) categories
      include (as a subset) all of B's categories. (See: lattice,
      lattice model.)

   $ dongle
      (I) A portable, physical, usually electronic device that is
      required to be attached to a computer to enable a particular
      software program to run. (See: token.)

      Tutorial: A dongle is essentially a physical key used for copy
      protection of software; that is, the program will not run unless
      the matching dongle is attached. When the software runs, it
      periodically queries the dongle and quits if the dongle does not
      reply with the proper authentication information. Dongles were
      originally constructed as an EPROM (erasable programmable read-
      only memory) to be connected to a serial input-output port of a
      personal computer.

   $ downgrade
      (I) /data security/ Reduce the security level of data (especially
      the classification level) without changing the information content
      of the data. (Compare: downgrade.)

   $ downgrade attack
      (I) A type of man-in-the-middle attack in which the attacker can
      cause two parties, at the time they negotiate a security
      association, to agree on a lower level of protection than the
      highest level that could have been supported by both of them.
      (Compare: downgrade.)

   $ draft RFC
      (D) A preliminary, temporary version of a document that is
      intended to become an RFC. (Compare: Internet-Draft.)

      Deprecated Term: IDOCs SHOULD NOT use this term. The RFC series is
      archival in nature and consists only of documents in permanent
      form. A document that is intended to become an RFC usually needs
      to be published first as an Internet-Draft (RFC 2026). (See:
      "Draft Standard" under "Internet Standard".)

   $ Draft Standard
      (I) See: secondary definition under "Internet Standard".

   $ DSA
      (N) See: Digital Signature Algorithm.

   $ DSS
      (N) See: Digital Signature Standard.

   $ dual control
      (I) A procedure that uses two or more entities (usually persons)
      operating in concert to protect a system resource, such that no
      single entity acting alone can access that resource. (See: no-lone
      zone, separation of duties, split knowledge.)

   $ dual signature
      (O) /SET/ A single digital signature that protects two separate
      messages by including the hash results for both sets in a single
      encrypted value. [SET2]

      Deprecated Usage: IDOCs SHOULD NOT use this term except when
      qualified as "SET(trademark) dual signature" with this definition.

      Tutorial: Generated by hashing each message separately,
      concatenating the two hash results, and then hashing that value
      and encrypting the result with the signer's private key. Done to
      reduce the number of encryption operations and to enable
      verification of data integrity without complete disclosure of the
      data.

   $ dual-use certificate
      (O) A certificate that is intended for use with both digital
      signature and data encryption services. [SP32]

      Usage: IDOCs that use this term SHOULD state a definition for it
      by identifying the intended uses of the certificate, because there
      are more than just these two uses mentioned in the NIST
      publication. A v3 X.509 public-key certificate may have a "key

      Usage" extension, which indicates the purposes for which the
      public key may be used. (See: certificate profile.)

   $ duty
      (I) An attribute of a role that obligates an entity playing the
      role to perform one or more tasks, which usually are essential for
      the functioning of the system. [Sand] (Compare authorization,
      privilege. See: role, billet.)

   $ e-cash
      (O) Electronic cash; money that is in the form of data and can be
      used as a payment mechanism on the Internet. (See: IOTP.)

      Usage: IDOCs that use this term SHOULD state a definition for it
      because many different types of electronic cash have been devised
      with a variety of security mechanisms.

   $ EAP
      (I) See: Extensible Authentication Protocol.

   $ EAL
      (O) See: evaluation assurance level.

   $ Easter egg
      (O) "Hidden functionality within an application program, which
      becomes activated when an undocumented, and often convoluted, set
      of commands and keystrokes is entered. Easter eggs are typically
      used to display the credits for the development team and [are]
      intended to be non-threatening" [SP28], but Easter eggs have the
      potential to contain malicious code.

      Deprecated Usage: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ eavesdropping
      (I) Passive wiretapping done secretly, i.e., without the knowledge
      of the originator or the intended recipients of the communication.

   $ ECB
      (N) See: electronic codebook.

   $ ECDSA
      (N) See: Elliptic Curve Digital Signature Algorithm.

   $ economy of alternatives
      (I) The principle that a security mechanism should be designed to
      minimize the number of alternative ways of achieving a service.
      (Compare: economy of mechanism.)

   $ economy of mechanism
      (I) The principle that a security mechanism should be designed to
      be as simple as possible, so that (a) the mechanism can be
      correctly implemented and (b) it can be verified that the
      operation of the mechanism enforces the system's security policy.
      (Compare: economy of alternatives, least privilege.)

   $ ECU
      (N) See: end cryptographic unit.

   $ EDI
      (I) See: electronic data interchange.

   $ EDIFACT
      (N) See: secondary definition under "electronic data interchange".

   $ EE
      (D) Abbreviation of "end entity" and other terms.

      Deprecated Abbreviation: IDOCs SHOULD NOT use this abbreviation;
      there could be confusion among "end entity", "end-to-end
      encryption", "escrowed encryption standard", and other terms.

   $ EES
      (O) See: Escrowed Encryption Standard.

   $ effective key length
      (O) "A measure of strength of a cryptographic algorithm,
      regardless of actual key length." [IATF] (See: work factor.)

   $ effectiveness
      (O) /ITSEC/ A property of a TOE representing how well it provides
      security in the context of its actual or proposed operational use.

   $ El Gamal algorithm
      (N) An algorithm for asymmetric cryptography, invented in 1985 by
      Taher El Gamal, that is based on the difficulty of calculating
      discrete logarithms and can be used for both encryption and
      digital signatures. [ElGa]

   $ electronic codebook (ECB)
      (N) A block cipher mode in which a plaintext block is used
      directly as input to the encryption algorithm and the resultant
      output block is used directly as cipher text [FP081]. (See: block
      cipher, [SP38A].)

   $ electronic commerce
      1. (I) Business conducted through paperless exchanges of
      information, using electronic data interchange, electronic funds
      transfer (EFT), electronic mail, computer bulletin boards,
      facsimile, and other paperless technologies.

      2. (O) /SET/ "The exchange of goods and services for payment
      between the cardholder and merchant when some or all of the
      transaction is performed via electronic communication." [SET2]

   $ electronic data interchange (EDI)
      (I) Computer-to-computer exchange, between trading partners, of
      business data in standardized document formats.

      Tutorial: EDI formats have been standardized primarily by ANSI X12
      and by EDIFACT (EDI for Administration, Commerce, and
      Transportation), which is an international, UN-sponsored standard
      primarily used in Europe and Asia. X12 and EDIFACT are aligning to
      create a single, global EDI standard.

   $ Electronic Key Management System (EKMS)
      (O) "Interoperable collection of systems developed by ... the U.S.
      Government to automate the planning, ordering, generating,
      distributing, storing, filling, using, and destroying of
      electronic keying material and the management of other types of
      COMSEC material." [C4009]

   $ electronic signature
      (D) Synonym for "digital signature" or "digitized signature".

      Deprecated Term: IDOCs SHOULD NOT use this term; there is no
      current consensus on its definition. Instead, use "digital
      signature", if that is what was intended

   $ electronic wallet
      (D) A secure container to hold, in digitized form, some sensitive
      data objects that belong to the owner, such as electronic money,
      authentication material, and various types of personal
      information. (See: IOTP.)

      Deprecated Term: IDOCs SHOULD NOT use this term. There is no
      current consensus on its definition; and some uses and definitions

      may be proprietary. Meanings range from virtual wallets
      implemented by data structures to physical wallets implemented by
      cryptographic tokens. (See: Deprecated Usage under "Green Book".)

   $ elliptic curve cryptography (ECC)
      (I) A type of asymmetric cryptography based on mathematics of
      groups that are defined by the points on a curve, where the curve
      is defined by a quadratic equation in a finite field. [Schn]

      Tutorial: ECC is based on mathematics different than that
      originally used to define the Diffie-Hellman-Merkle algorithm and
      the DSA, but ECC can be used to define an algorithm for key
      agreement that is an analog of Diffie-Hellman-Merkle [A9063] and
      an algorithm for digital signature that is an analog of DSA
      [A9062]. The mathematical problem upon which ECC is based is
      believed to be more difficult than the problem upon which Diffie-
      Hellman-Merkle is based and, therefore, that keys for ECC can be
      shorter for a comparable level of security. (See: ECDSA.)

   $ Elliptic Curve Digital Signature Algorithm (ECDSA)
      (N) A standard [A9062] that is the analog, in elliptic curve
      cryptography, of the Digital Signature Algorithm.

   $ emanation
      (I) A signal (e.g., electromagnetic or acoustic) that is emitted
      by a system (e.g., through radiation or conductance) as a
      consequence (i.e., byproduct) of the system's operation, and that
      may contain information. (See: emanations security.)

   $ emanations analysis
      (I) /threat action/ See: secondary definition under
      "interception".

   $ emanations security (EMSEC)
      (I) Physical security measures to protect against data compromise
      that could occur because of emanations that might be received and
      read by an unauthorized party. (See: emanation, TEMPEST.)

      Usage: Refers either to preventing or limiting emanations from a
      system and to preventing or limiting the ability of unauthorized
      parties to receive the emissions.

   $ embedded cryptography
      (N) "Cryptography engineered into an equipment or system whose
      basic function is not cryptographic." [C4009]

   $ emergency plan
      (D) Synonym for "contingency plan".

      Deprecated Term: IDOCs SHOULD NOT use this term. Instead, for
      neutrality and consistency of language, use "contingency plan".

   $ emergency response
      (O) An urgent response to a fire, flood, civil commotion, natural
      disaster, bomb threat, or other serious situation, with the intent
      of protecting lives, limiting damage to property, and minimizing
      disruption of system operations. [FP087] (See: availability, CERT,
      emergency plan.)

   $ EMSEC
      (I) See: emanations security.

   $ EMV
      (N) Abbreviation of "Europay, MasterCard, Visa". Refers to a
      specification for smart cards that are used as payment cards, and
      for related terminals and applications. [EMV1, EMV2, EMV3]

   $ Encapsulating Security Payload (ESP)
      (I) An Internet protocol [R2406, R4303] designed to provide data
      confidentiality service and other security services for IP
      datagrams. (See: IPsec. Compare: AH.)

      Tutorial: ESP may be used alone, or in combination with AH, or in
      a nested fashion with tunneling. Security services can be provided
      between a pair of communicating hosts, between a pair of
      communicating security gateways, or between a host and a gateway.
      The ESP header is encapsulated by the IP header, and the ESP
      header encapsulates either the upper-layer protocol header
      (transport mode) or an IP header (tunnel mode). ESP can provide
      data confidentiality service, data origin authentication service,
      connectionless data integrity service, an anti-replay service, and
      limited traffic-flow confidentiality. The set of services depends
      on the placement of the implementation and on options selected
      when the security association is established.

   $ encipher
      (D) Synonym for "encrypt".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "encrypt". However, see Usage note under "encryption".

   $ encipherment
      (D) Synonym for "encryption".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "encryption". However, see Usage note under "encryption".

   $ enclave
      1. (I) A set of system resources that operate in the same security
      domain and that share the protection of a single, common,
      continuous security perimeter. (Compare: domain.)

      2. (D) /U.S. Government/ "Collection of computing environments
      connected by one or more internal networks under the control of a
      single authority and security policy, including personnel and
      physical security." [C4009]

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 2 because the definition applies to what is usually
      called a "security domain". That is, a security domain is a set of
      one or more security enclaves.

   $ encode
      1. (I) Use a system of symbols to represent information, which
      might originally have some other representation. Example: Morse
      code. (See: ASCII, BER.) (See: code, decode.)

      2. (D) Synonym for "encrypt".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "encrypt"; encoding is not always meant to conceal meaning.

   $ encrypt
      (I) Cryptographically transform data to produce cipher text. (See:
      encryption. Compare: seal.)

   $ encryption
      1. (I) Cryptographic transformation of data (called "plain text")
      into a different form (called "cipher text") that conceals the
      data's original meaning and prevents the original form from being
      used. The corresponding reverse process is "decryption", a
      transformation that restores encrypted data to its original form.
      (See: cryptography.)

      2. (O) "The cryptographic transformation of data to produce
      ciphertext." [I7498-2]

      Usage: For this concept, IDOCs SHOULD use the verb "to encrypt"
      (and related variations: encryption, decrypt, and decryption).
      However, because of cultural biases involving human burial, some
      international documents (particularly ISO and CCITT standards)
      avoid "to encrypt" and instead use the verb "to encipher" (and
      related variations: encipherment, decipher, decipherment).

      Tutorial: Usually, the plaintext input to an encryption operation
      is clear text. But in some cases, the plain text may be cipher
      text that was output from another encryption operation. (See:
      superencryption.)

      Encryption and decryption involve a mathematical algorithm for
      transforming data. Besides the data to be transformed, the
      algorithm has one or more inputs that are control parameters: (a)
      a key that varies the transformation and, in some cases, (b) an IV
      that establishes the starting state of the algorithm.

   $ encryption certificate
      (I) A public-key certificate that contains a public key that is
      intended to be used for encrypting data, rather than for verifying
      digital signatures or performing other cryptographic functions.

      Tutorial: A v3 X.509 public-key certificate may have a "keyUsage"
      extension that indicates the purpose for which the certified
      public key is intended. (See: certificate profile.)

   $ end cryptographic unit (ECU)
      1. (N) Final destination device into which a key is loaded for
      operational use.

      2. (N) A device that (a) performs cryptographic functions, (b)
      typically is part of a larger system for which the device provides
      security services, and (c), from the viewpoint of a supporting
      security infrastructure such as a key management system, is the
      lowest level of identifiable component with which a management
      transaction can be conducted

   $ end entity
      1. (I) A system entity that is the subject of a public-key
      certificate and that is using, or is permitted and able to use,
      the matching private key only for purposes other than signing a
      digital certificate; i.e., an entity that is not a CA.

      2. (O) "A certificate subject [that] uses its public [sic] key for
      purposes other than signing certificates." [X509]

      Deprecated Definition: IDOCs SHOULD NOT use definition 2, which is
      misleading and incomplete. First, that definition should have said
      "private key" rather than "public key" because certificates are
      not usefully signed with a public key. Second, the X.509
      definition is ambiguous regarding whether an end entity may or may
      not use the private key to sign a certificate, i.e., whether the
      subject may be a CA. The intent of X.509's authors was that an end
      entity certificate is not valid for use in verifying a signature

      on an X.509 certificate or X.509 CRL. Thus, it would have been
      better for the X.509 definition to have said "only for purposes
      other than signing certificates".

      Usage: Despite the problems in the X.509 definition, the term
      itself is useful in describing applications of asymmetric
      cryptography. The way the term is used in X.509 implies that it
      was meant to be defined, as we have done here, relative to roles
      that an entity (which is associated with an OSI end system) is
      playing or is permitted to play in applications of asymmetric
      cryptography other than the PKI that supports applications.

      Tutorial: Whether a subject can play both CA and non-CA roles,
      with either the same or different certificates, is a matter of
      policy. (See: CPS.) A v3 X.509 public-key certificate may have a
      "basicConstraints" extension containing a "cA" value that
      specifically "indicates whether or not the public key may be used
      to verify certificate signatures". (See: certificate profile.)

   $ end system
      (N) /OSIRM/ A computer that implements all seven layers of the
      OSIRM and may attach to a subnetwork. Usage: In the IPS context,
      an end system is called a "host".

   $ end-to-end encryption
      (I) Continuous protection of data that flows between two points in
      a network, effected by encrypting data when it leaves its source,
      keeping it encrypted while it passes through any intermediate
      computers (such as routers), and decrypting it only when it
      arrives at the intended final destination. (See: wiretapping.
      Compare: link encryption.)

      Examples: A few are BLACKER, CANEWARE, IPLI, IPsec, PLI, SDNS,
      SILS, SSH, SSL, TLS.

      Tutorial: When two points are separated by multiple communication
      links that are connected by one or more intermediate relays, end-
      to-end encryption enables the source and destination systems to
      protect their communications without depending on the intermediate
      systems to provide the protection.

   $ end user
      1. (I) /information system/ A system entity, usually a human
      individual, that makes use of system resources, primarily for
      application purposes as opposed to system management purposes.

      2. (D) /PKI/ Synonym for "end entity".

      Deprecated Definition: IDOCs SHOULD NOT use "end user" as a
      synonym for "end entity", because that would mix concepts in a
      potentially misleading way.

   $ endorsed-for-unclassified cryptographic item (EUCI)
      (O) /U.S. Government/ "Unclassified cryptographic equipment that
      embodies a U.S. Government classified cryptographic logic and is
      endorsed by NSA for the protection of national security
      information." [C4009] (Compare: CCI, type 2 product.)

   $ entity
      See: system entity.

   $ entrapment
      (I) "The deliberate planting of apparent flaws in a system for the
      purpose of detecting attempted penetrations or confusing an
      intruder about which flaws to exploit." [FP039] (See: honey pot.)

   $ entropy
      1. (I) An information-theoretic measure (usually stated as a
      number of bits) of the amount of uncertainty that an attacker
      faces to determine the value of a secret. [SP63] (See: strength.)

      Example: If a password is said to contain at least 20 bits of
      entropy, that means that it must be as hard to find the password
      as to guess a 20-bit random number.

      2. (I) An information-theoretic measure (usually stated as a
      number of bits) of the amount of information in a message; i.e.,
      the minimum number of bits needed to encode all possible meanings
      of that message. [Schn] (See: uncertainty.)

   $ ephemeral
      (I) /adjective/ Refers to a cryptographic key or other
      cryptographic parameter or data object that is short-lived,
      temporary, or used one time. (See: session key. Compare: static.)

   $ erase
      1. (I) Delete stored data. (See: sanitize, zeroize.)

      2. (O) /U.S. Government/ Delete magnetically stored data in such a
      way that the data cannot be recovered by ordinary means, but might
      be recoverable by laboratory methods. [C4009] (Compare: /U.S.
      Government/ purge.)

   $ error detection code
      (I) A checksum designed to detect, but not correct, accidental
      (i.e., unintentional) changes in data.

   $ Escrowed Encryption Standard (EES)
      (N) A U.S. Government standard [FP185] that specifies how to use a
      symmetric encryption algorithm (SKIPJACK) and create a Law
      Enforcement Access Field (LEAF) for implementing part of a key
      escrow system that enables decryption of telecommunications when
      interception is lawfully authorized.

      Tutorial: Both SKIPJACK and the LEAF are intended for use in
      equipment used to encrypt and decrypt sensitive, unclassified,
      telecommunications data.

   $ ESP
      (I) See: Encapsulating Security Payload.

   $ Estelle
      (N) A language (ISO 9074-1989) for formal specification of
      computer network protocols.

   $ ETSI
      (N) See: European Telecommunication Standards Institute.

   $ EUCI
      (O) See: endorsed-for-unclassified cryptographic item.

   $ European Telecommunication Standards Institute (ETSI)
      (N) An independent, non-profit organization, based in France, that
      is officially recognized by the European Commission and
      responsible for standardization of information and communication
      technologies within Europe.

      Tutorial: ETSI maintains the standards for a number of security
      algorithms, including encryption algorithms for mobile telephone
      systems in Europe.

   $ evaluated system
      (I) A system that has been evaluated against security criteria
      (for example, against the TCSEC or against a profile based on the
      Common Criteria).

   $ evaluation
      (I) Assessment of an information system against defined security
      criteria (for example, against the TCSEC or against a profile
      based on the Common Criteria). (Compare: certification.)

   $ evaluation assurance level (EAL)
      (N) A predefined package of assurance components that represents a
      point on the Common Criteria's scale for rating confidence in the
      security of information technology products and systems.

      Tutorial: The Common Criteria defines a scale of seven,
      hierarchically ordered EALs for rating a TOE. From highest to
      lowest, they are as follows:
      -  EAL7. Formally verified design and tested.
      -  EAL6. Semiformally verified design and tested.
      -  EAL5. Semiformally designed and tested.
      -  EAL4. Methodically designed, tested, and reviewed.
      -  EAL3. Methodically tested and checked.
      -  EAL2. Structurally tested.
      -  EAL1. Functionally tested.

      An EAL is a consistent, baseline set of requirements. The increase
      in assurance from EAL to EAL is accomplished by substituting
      higher assurance components (i.e., criteria of increasing rigor,
      scope, or depth) from seven assurance classes: (a) configuration
      management, (b) delivery and operation, (c) development, (d)
      guidance documents, (e) lifecycle support, (f) tests, and (g)
      vulnerability assessment.

      The EALs were developed with the goal of preserving concepts of
      assurance that were adopted from earlier criteria, so that results
      of previous evaluations would remain relevant. For example, EALs
      levels 2-7 are generally equivalent to the assurance portions of
      the TCSEC C2-A1 scale. However, this equivalency should be used
      with caution. The levels do not derive assurance in the same
      manner, and exact mappings do not exist.

   $ expire
      (I) /credential/ Cease to be valid (i.e., change from being valid
      to being invalid) because its assigned lifetime has been exceeded.
      (See: certificate expiration.)

   $ exposure
      (I) A type of threat action whereby sensitive data is directly
      released to an unauthorized entity. (See: unauthorized
      disclosure.)

      Usage: This type of threat action includes the following subtypes:
      -  "Deliberate Exposure": Intentional release of sensitive data to
         an unauthorized entity.
      -  "Scavenging": Searching through data residue in a system to
         gain unauthorized knowledge of sensitive data.
      -  "Human error": /exposure/ Human action or inaction that
         unintentionally results in an entity gaining unauthorized
         knowledge of sensitive data. (Compare: corruption,
         incapacitation.)
      -  "Hardware or software error": /exposure/ System failure that
         unintentionally results in an entity gaining unauthorized

         knowledge of sensitive data. (Compare: corruption,
         incapacitation.)

   $ Extended Security Option
      (I) See: secondary definition under "IPSO".

   $ Extensible Authentication Protocol (EAP)
      (I) An extension framework for PPP that supports multiple,
      optional authentication mechanisms, including cleartext passwords,
      challenge-response, and arbitrary dialog sequences. [R3748]
      (Compare: GSS-API, SASL.)

      Tutorial: EAP typically runs directly over IPS data link protocols
      or OSIRM Layer 2 protocols, i.e., without requiring IP.
      Originally, EAP was developed for use in PPP, by a host or router
      that connects to a network server via switched circuits or dial-up
      lines. Today, EAP's domain of applicability includes other areas
      of network access control; it is used in wired and wireless LANs
      with IEEE 802.1X, and in IPsec with IKEv2. EAP is conceptually
      related to other authentication mechanism frameworks, such as SASL
      and GSS-API.

   $ Extensible Markup Language (XML)
      (N) A version of Standard Generalized Markup Language (ISO 8879)
      that separately represents a document's content and its structure.
      XML was designed by W3C for use on the World Wide Web.

   $ extension
      (I) /protocol/ A data item or a mechanism that is defined in a
      protocol to extend the protocol's basic or original functionality.

      Tutorial: Many protocols have extension mechanisms, and the use of
      these extension is usually optional. IP and X.509 are two examples
      of protocols that have optional extensions. In IP version 4,
      extensions are called "options", and some of the options have
      security purposes (see: IPSO).

      In X.509, certificate and CRL formats can be extended to provide
      methods for associating additional attributes with subjects and
      public keys and for managing a certification hierarchy:
      -  A "certificate extension": X.509 defines standard extensions
         that may be included in v3 certificates to provide additional
         key and security policy information, subject and issuer
         attributes, and certification path constraints.
      -  A "CRL extension": X.509 defines extensions that may be
         included in v2 CRLs to provide additional issuer key and name
         information, revocation reasons and constraints, and
         information about distribution points and delta CRLs.

      -  A "private extension": Additional extensions, each named by an
         OID, can be locally defined as needed by applications or
         communities. (See: Authority Information Access extension, SET
         private extensions.)

   $ external controls
      (I) /COMPUSEC/ Refers to administrative security, personnel
      security, and physical security. (Compare: internal controls.)

   $ extranet
      (I) A computer network that an organization uses for application
      data traffic between the organization and its business partners.
      (Compare: intranet.)

      Tutorial: An extranet can be implemented securely, either on the
      Internet or using Internet technology, by constructing the
      extranet as a VPN.

   $ extraction resistance
      (O) Ability of cryptographic equipment to resist efforts to
      extract keying material directly from the equipment (as opposed to
      gaining knowledge of keying material by cryptanalysis). [C4009]

   $ extrusion detection
      (I) Monitoring for unauthorized transfers of sensitive information
      and other communications that originate inside a system's security
      perimeter and are directed toward the outside; i.e., roughly the
      opposite of "intrusion detection".

   $ fail-safe
      1. (I) Synonym for "fail-secure".

      2. (I) A mode of termination of system functions that prevents
      damage to specified system resources and system entities (i.e.,
      specified data, property, and life) when a failure occurs or is
      detected in the system (but the failure still might cause a
      security compromise). (See: failure control.)

      Tutorial: Definitions 1 and 2 are opposing design alternatives.
      Therefore, IDOCs SHOULD NOT use this term without providing a
      definition for it. If definition 1 is intended, IDOCs can avoid
      ambiguity by using "fail-secure" instead.

   $ fail-secure
      (I) A mode of termination of system functions that prevents loss
      of secure state when a failure occurs or is detected in the system
      (but the failure still might cause damage to some system resource
      or system entity). (See: failure control. Compare: fail-safe.)

   $ fail-soft
      (I) Selective termination of affected, non-essential system
      functions when a failure occurs or is detected in the system.
      (See: failure control.)

   $ failure control
      (I) A methodology used to provide fail-safe, fail-secure or fail-
      soft termination and recovery of system functions. [FP039]

   $ fairness
      (I) A property of an access protocol for a system resource whereby
      the resource is made equitably or impartially available to all
      eligible users. (RFC 3753)

      Tutorial: Fairness can be used to defend against some types of
      denial-of-service attacks on a system connected to a network.
      However, this technique assumes that the system can properly
      receive and process inputs from the network. Therefore, the
      technique can mitigate flooding but is ineffective against
      jamming.

   $ falsification
      (I) A type of threat action whereby false data deceives an
      authorized entity. (See: active wiretapping, deception.)

      Usage: This type of threat action includes the following subtypes:
      -  "Substitution": Altering or replacing valid data with false
         data that serves to deceive an authorized entity.
      -  "Insertion": Introducing false data that serves to deceive an
         authorized entity.

   $ fault tree
      (I) A branching, hierarchical data structure that is used to
      represent events and to determine the various combinations of
      component failures and human acts that could result in a specified
      undesirable system event. (See: attack tree, flaw hypothesis
      methodology.)

      Tutorial: "Fault-tree analysis" is a technique in which an
      undesired state of a system is specified and the system is studied
      in the context of its environment and operation to find all
      credible ways in which the event could occur. The specified fault
      event is represented as the root of the tree. The remainder of the
      tree represents AND or OR combinations of subevents, and
      sequential combinations of subevents, that could cause the root
      event to occur. The main purpose of a fault-tree analysis is to
      calculate the probability of the root event, using statistics or
      other analytical methods and incorporating actual or predicted

      quantitative reliability and maintainability data. When the root
      event is a security violation, and some of the subevents are
      deliberate acts intended to achieve the root event, then the fault
      tree is an attack tree.

   $ FEAL
      (O) A family of symmetric block ciphers that was developed in
      Japan; uses a 64-bit block, keys of either 64 or 128 bits, and a
      variable number of rounds; and has been successfully attacked by
      cryptanalysts. [Schn]

   $ Federal Information Processing Standards (FIPS)
      (N) The Federal Information Processing Standards Publication (FIPS
      PUB) series issued by NIST under the provisions of Section 111(d)
      of the Federal Property and Administrative Services Act of 1949 as
      amended by the Computer Security Act of 1987 (Public Law 100-235)
      as technical guidelines for U.S. Government procurements of
      information processing system equipment and services. (See:
      "[FPxxx]" items in Section 7, Informative References.)

   $ Federal Public-key Infrastructure (FPKI)
      (O) A PKI being planned to establish facilities, specifications,
      and policies needed by the U.S. Government to use public-key
      certificates in systems involving unclassified but sensitive
      applications and interactions between Federal agencies as well as
      with entities of state and local governments, the business
      community, and the public. [FPKI]

   $ Federal Standard 1027
      (N) An U.S. Government document defining emanation, anti-tamper,
      security fault analysis, and manual key management criteria for
      DES encryption devices, primary for OSIRM Layer 2. Was renamed
      "FIPS PUB 140" when responsibility for protecting unclassified,
      sensitive information was transferred from NSA to NIST, and has
      since been superseded by newer versions of that standard [FP140].

   $ File Transfer Protocol (FTP)
      (I) A TCP-based, Application-Layer, Internet Standard protocol
      (RFC 959) for moving data files from one computer to another.

   $ fill device
      (N) /COMSEC/ A device used to transfer or store keying material in
      electronic form or to insert keying material into cryptographic
      equipment.

   $ filter
      1. (I) /noun/ Synonym for "guard". (Compare: content filter,
      filtering router.)

      2. (I) /verb/ To process a flow of data and selectively block
      passage or permit passage of individual data items according to a
      security policy.

   $ filtering router
      (I) An internetwork router that selectively prevents the passage
      of data packets according to a security policy. (See: guard.)

      Tutorial: A router usually has two or more physical connections to
      networks or other systems; and when the router receives a packet
      on one of those connections, it forwards the packet on a second
      connection. A filtering router does the same; but it first
      decides, according to some security policy, whether the packet
      should be forwarded at all. The policy is implemented by rules
      (packet filters) loaded into the router. The rules mostly involve
      values of data packet control fields (especially IP source and
      destination addresses and TCP port numbers) [R2179]. A filtering
      router may be used alone as a simple firewall or be used as a
      component of a more complex firewall.

   $ financial institution
      (N) "An establishment responsible for facilitating customer-
      initiated transactions or transmission of funds for the extension
      of credit or the custody, loan, exchange, or issuance of money."
      [SET2]

   $ fingerprint
      1. (I) A pattern of curves formed by the ridges on a fingertip.
      (See: biometric authentication. Compare: thumbprint.)

      2. (D) /PGP/ A hash result ("key fingerprint") used to
      authenticate a public key or other data. [PGP]

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 2, and SHOULD NOT use this term as a synonym for "hash
      result" of *any* kind. Either use would mix concepts in a
      potentially misleading way.

   $ FIPS
      (N) See: Federal Information Processing Standards.

   $ FIPS PUB 140
      (N) The U.S. Government standard [FP140] for security requirements
      to be met by a cryptographic module when the module is used to
      protect unclassified information in computer and communication
      systems. (See: Common Criteria, FIPS, Federal Standard 1027.)

      Tutorial: The standard specifies four increasing levels (from
      "Level 1" to "Level 4") of requirements to cover a wide range of
      potential applications and environments. The requirements address
      basic design and documentation, module interfaces, authorized
      roles and services, physical security, software security,
      operating system security, key management, cryptographic
      algorithms, electromagnetic interference and electromagnetic
      compatibility (EMI/EMC), and self-testing. NIST and the Canadian
      Communication Security Establishment jointly certify modules.

   $ FIREFLY
      (O) /U.S. Government/ "Key management protocol based on public-key
      cryptography." [C4009]

   $ firewall
      1. (I) An internetwork gateway that restricts data communication
      traffic to and from one of the connected networks (the one said to
      be "inside" the firewall) and thus protects that network's system
      resources against threats from the other network (the one that is
      said to be "outside" the firewall). (See: guard, security
      gateway.)

      2. (O) A device or system that controls the flow of traffic
      between networks using differing security postures. [SP41]

      Tutorial: A firewall typically protects a smaller, secure network
      (such as a corporate LAN, or even just one host) from a larger
      network (such as the Internet). The firewall is installed at the
      point where the networks connect, and the firewall applies policy
      rules to control traffic that flows in and out of the protected
      network.

      A firewall is not always a single computer. For example, a
      firewall may consist of a pair of filtering routers and one or
      more proxy servers running on one or more bastion hosts, all
      connected to a small, dedicated LAN (see: buffer zone) between the
      two routers. The external router blocks attacks that use IP to
      break security (IP address spoofing, source routing, packet
      fragments), while proxy servers block attacks that would exploit a
      vulnerability in a higher-layer protocol or service. The internal
      router blocks traffic from leaving the protected network except
      through the proxy servers. The difficult part is defining criteria
      by which packets are denied passage through the firewall, because
      a firewall not only needs to keep unauthorized traffic (i.e.,
      intruders) out, but usually also needs to let authorized traffic
      pass both in and out.

   $ firmware
      (I) Computer programs and data stored in hardware -- typically in
      read-only memory (ROM) or programmable read-only memory (PROM) --
      such that the programs and data cannot be dynamically written or
      modified during execution of the programs. (See: hardware,
      software.)

   $ FIRST
      (N) See: Forum of Incident Response and Security Teams.

   $ flaw
      1. (I) An error in the design, implementation, or operation of an
      information system. A flaw may result in a vulnerability.
      (Compare: vulnerability.)

      2. (D) "An error of commission, omission, or oversight in a system
      that allows protection mechanisms to be bypassed." [NCSSG]
      (Compare: vulnerability. See: brain-damaged.)

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 2; not every flaw is a vulnerability.

   $ flaw hypothesis methodology
      (I) An evaluation or attack technique in which specifications and
      documentation for a system are analyzed to hypothesize flaws in
      the system. The list of hypothetical flaws is prioritized on the
      basis of the estimated probability that a flaw exists and,
      assuming it does, on the ease of exploiting it and the extent of
      control or compromise it would provide. The prioritized list is
      used to direct a penetration test or attack against the system.
      [NCS04] (See: fault tree, flaw.)

   $ flooding
      1. (I) An attack that attempts to cause a failure in a system by
      providing more input than the system can process properly. (See:
      denial of service, fairness. Compare: jamming.)

      Tutorial: Flooding uses "overload" as a type of "obstruction"
      intended to cause "disruption".

      2. (I) The process of delivering data or control messages to every
      node of a network. (RFC 3753)

   $ flow analysis
      (I) An analysis performed on a nonprocedural, formal, system
      specification that locates potential flows of information between
      system variables. By assigning security levels to the variables,
      the analysis can find some types of covert channels. [Huff]

   $ flow control
      1. (I) /data security/ A procedure or technique to ensure that
      information transfers within a system are not made from one
      security level to another security level, and especially not from
      a higher level to a lower level. [Denns] (See: covert channel,
      confinement property, information flow policy, simple security
      property.)

      2. (O) /data security/ "A concept requiring that information
      transfers within a system be controlled so that information in
      certain types of objects cannot, via any channel within the
      system, flow to certain other types of objects." [NCSSG]

   $ For Official Use Only (FOUO)
      (O) /U.S. DoD/ A U.S. Government designation for information that
      has not been given a security classification pursuant to the
      criteria of an Executive Order dealing with national security, but
      which may be withheld from the public because disclosure would
      cause a foreseeable harm to an interest protected by one of the
      exemptions stated in the Freedom of Information Act (Section 552
      of title 5, United States Code). (See: security label, security
      marking. Compare: classified.)

   $ formal
      (I) Expressed in a restricted syntax language with defined
      semantics based on well-established mathematical concepts. [CCIB]
      (Compare: informal, semiformal.)

   $ formal access approval
      (O) /U.S. Government/ Documented approval by a data owner to allow
      access to a particular category of information in a system. (See:
      category.)

   $ Formal Development Methodology
      (O) See: Ina Jo.

   $ formal model
      (I) A security model that is formal. Example: Bell-LaPadula model.
      [Land] (See: formal, security model.)

   $ formal proof
      (I) "A complete and convincing mathematical argument, presenting
      the full logical justification for each step in the proof, for the
      truth of a theorem or set of theorems." [NCSSG]

   $ formal specification
      (I) A precise description of the (intended) behavior of a system,
      usually written in a mathematical language, sometimes for the

      purpose of supporting formal verification through a correctness
      proof. [Huff] (See: Affirm, Gypsy, HDM, Ina Jo.) (See: formal.)

      Tutorial: A formal specification can be written at any level of
      detail but is usually a top-level specification.

   $ formal top-level specification
      (I) "A top-level specification that is written in a formal
      mathematical language to allow theorems showing the correspondence
      of the system specification to its formal requirements to be
      hypothesized and formally proven." [NCS04] (See: formal
      specification.)

   $ formulary
      (I) A technique for enabling a decision to grant or deny access to
      be made dynamically at the time the access is attempted, rather
      than earlier when an access control list or ticket is created.

   $ FORTEZZA(trademark)
      (O) A registered trademark of NSA, used for a family of
      interoperable security products that implement a NIST/NSA-approved
      suite of cryptographic algorithms for digital signature, hash,
      encryption, and key exchange. The products include a PC card
      (which contains a CAPSTONE chip), and compatible serial port
      modems, server boards, and software implementations.

   $ Forum of Incident Response and Security Teams (FIRST)
      (N) An international consortium of CSIRTs (e.g., CIAC) that work
      together to handle computer security incidents and promote
      preventive activities. (See: CSIRT, security incident.)

      Tutorial: FIRST was founded in 1990 and, as of July 2004, had more
      than 100 members spanning the globe. Its mission includes:
      -  Provide members with technical information, tools, methods,
         assistance, and guidance.
      -  Coordinate proactive liaison activities and analytical support.
      -  Encourage development of quality products and services.
      -  Improve national and international information security for
         governments, private industry, academia, and the individual.
      -  Enhance the image and status of the CSIRT community.

   $ forward secrecy
      (I) See: perfect forward secrecy.

   $ FOUO
      (O) See: For Official Use Only.

   $ FPKI
      (O) See: Federal Public-Key Infrastructure.

   $ fraggle attack
      (D) /slang/ A synonym for "smurf attack".

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term.

      Derivation: The Fraggles are a fictional race of small humanoids
      (represented as hand puppets in a children's television series,
      "Fraggle Rock") that live underground.

   $ frequency hopping
      (N) Repeated switching of frequencies during radio transmission
      according to a specified algorithm. [C4009] (See: spread
      spectrum.)

      Tutorial: Frequency hopping is a TRANSEC technique to minimize the
      potential for unauthorized interception or jamming.

   $ fresh
      (I) Recently generated; not replayed from some earlier interaction
      of the protocol.

      Usage: Describes data contained in a PDU that is received and
      processed for the first time. (See: liveness, nonce, replay
      attack.)

   $ FTP
      (I) See: File Transfer Protocol.

   $ gateway
      (I) An intermediate system (interface, relay) that attaches to two
      (or more) computer networks that have similar functions but
      dissimilar implementations and that enables either one-way or two-
      way communication between the networks. (See: bridge, firewall,
      guard, internetwork, proxy server, router, and subnetwork.)

      Tutorial: The networks may differ in any of several aspects,
      including protocols and security mechanisms. When two computer
      networks differ in the protocol by which they offer service to
      hosts, a gateway may translate one protocol into the other or
      otherwise facilitate interoperation of hosts (see: Internet
      Protocol). In theory, gateways between computer networks are
      conceivable at any OSIRM layer. In practice, they usually operate

      at OSIRM Layer 2 (see: bridge), 3 (see: router), or 7 (see: proxy
      server).

   $ GCA
      (O) See: geopolitical certificate authority.

   $ GDOI
      (O) See: Group Domain of Interpretation.

   $ GeldKarte
      (O) A smartcard-based, electronic money system that is maintained
      by the German banking industry, incorporates cryptography, and can
      be used to make payments via the Internet. (See: IOTP.)

   $ GeneralizedTime
      (N) The ASN.1 data type "GeneralizedTime" (ISO 8601) contains a
      calendar date (YYYYMMDD) and a time of day, which is either (a)
      the local time, (b) the Coordinated Universal Time, or (c) both
      the local time and an offset that enables Coordinated Universal
      Time to be calculated. (See: Coordinated Universal Time. Compare:
      UTCTime.)

   $ Generic Security Service Application Program Interface (GSS-API)
      (I) An Internet Standard protocol [R2743] that specifies calling
      conventions by which an application (typically another
      communication protocol) can obtain authentication, integrity, and
      confidentiality security services independently of the underlying
      security mechanisms and technologies, thus enabling the
      application source code to be ported to different environments.
      (Compare: EAP, SASL.)

      Tutorial: "A GSS-API caller accepts tokens provided to it by its
      local GSS-API implementation and transfers the tokens to a peer on
      a remote system; that peer passes the received tokens to its local
      GSS-API implementation for processing. The security services
      available through GSS-API in this fashion are implementable (and
      have been implemented) over a range of underlying mechanisms based
      on [symmetric] and [asymmetric cryptography]." [R2743]

   $ geopolitical certificate authority (GCA)
      (O) /SET/ In a SET certification hierarchy, an optional level that
      is certified by a BCA and that may certify cardholder CAs,
      merchant CAs, and payment gateway CAs. Using GCAs enables a brand
      to distribute responsibility for managing certificates to
      geographic or political regions, so that brand policies can vary
      between regions as needed.

   $ GIG
      (O) See: Global Information Grid.

   $ Global Information Grid (GIG)
      (O) /U.S. DoD/ The GIG is "a globally interconnected, end-to-end
      set of information capabilities, associated processes and
      personnel for collecting, processing, storing, disseminating, and
      managing information on demand to war fighters, policy makers, and
      support personnel." [IATF] Usage: Formerly referred to as the DII.

   $ good engineering practice(s)
      (N) A term used to specify or characterize design, implementation,
      installation, or operating practices for an information system,
      when a more explicit specification is not possible. Generally
      understood to refer to the state of the engineering art for
      commercial systems that have problems and solutions equivalent to
      the system in question.

   $ granularity
      1. (N) /access control/ Relative fineness to which an access
      control mechanism can be adjusted.

      2. (N) /data security/ "The size of the smallest protectable unit
      of information" in a trusted system. [Huff]

   $ Green Book
      (D) /slang/ Synonym for "Defense Password Management Guideline"
      [CSC2].

      Deprecated Term: Except as an explanatory appositive, IDOCs SHOULD
      NOT use this term, regardless of the associated definition.
      Instead, use the full proper name of the document or, in
      subsequent references, a conventional abbreviation. (See: Rainbow
      Series.)

      Deprecated Usage: To improve international comprehensibility of
      Internet Standards and the Internet Standards Process, IDOCs
      SHOULD NOT use "cute" synonyms. No matter how clearly understood
      or popular a nickname may be in one community, it is likely to
      cause confusion or offense in others. For example, several other
      information system standards also are called "the Green Book"; the
      following are some examples:
      -  Each volume of 1992 ITU-T (known at that time as CCITT)
         standards.
      -  "PostScript Language Program Design", Adobe Systems, Addison-
         Wesley, 1988.
      -  IEEE 1003.1 POSIX Operating Systems Interface.

      -  "Smalltalk-80: Bits of History, Words of Advice", Glenn
         Krasner, Addison-Wesley, 1983.
      -  "X/Open Compatibility Guide".
      -  A particular CD-ROM format developed by Phillips.

   $ Group Domain of Interpretation (GDOI)
      (I) An ISAKMP/IKE domain of interpretation for group key
      management; i.e., a phase 2 protocol in ISAKMP. [R3547] (See:
      secure multicast.)

      Tutorial: In this group key management model that extends the
      ISAKMP standard, the protocol is run between a group member and a
      "group controller/key server", which establishes security
      associations [R4301] among authorized group members. The GDOI
      protocol is itself protected by an ISAKMP phase 1 association.

      For example, multicast applications may use ESP to protect their
      data traffic. GDOI carries the needed security association
      parameters for ESP. In this way, GDOI supports multicast ESP with
      group authentication of ESP packets using a shared, group key.

   $ group identity
      (I) See: secondary definition under "identity".

   $ group security association
      (I) "A bundling of [security associations] (SAs) that together
      define how a group communicates securely. The [group SA] may
      include a registration protocol SA, a rekey protocol SA, and one
      or more data security protocol SAs." [R3740]

   $ GSS-API
      (I) See: Generic Security Service Application Program Interface.

   $ guard
      (I) A computer system that (a) acts as gateway between two
      information systems operating under different security policies
      and (b) is trusted to mediate information data transfers between
      the two. (See: controlled interface, cross-domain solution,
      domain, filter. Compare: firewall.)

      Usage: Frequently understood to mean that one system is operating
      at a higher security level than the other, and that the gateway's
      purpose is to prevent unauthorized disclosure of data from the
      higher system to the lower. However, the purpose might also be to
      protect the data integrity, availability, or general system
      integrity of one system from threats posed by connecting to the
      other system. The mediation may be entirely automated or may
      involve "reliable human review".

   $ guest login
      (I) See: anonymous login.

   $ GULS
      (I) Generic Upper Layer Security service element (ISO 11586), a
      five-part standard for the exchange of security information and
      security-transformation functions that protect confidentiality and
      integrity of application data.

   $ Gypsy verification environment
      (O) A methodology, language, and integrated set of software tools
      developed at the University of Texas for specifying, coding, and
      verifying software to produce correct and reliable programs.
      [Cheh]

   $ H field
      (D) See: Deprecated Usage under "Handling Restrictions field".

   $ hack
      1a. (I) /verb/ To work on something, especially to program a
      computer. (See: hacker.)

      1b. (I) /verb/ To do some kind of mischief, especially to play a
      prank on, or penetrate, a system. (See: hacker, cracker.)

      2. (I) /noun/ An item of completed work, or a solution for a
      problem, that is non-generalizable, i.e., is very specific to the
      application area or problem being solved.

      Tutorial: Often, the application area or problem involves computer
      programming or other use of a computer. Characterizing something
      as a hack can be a compliment, such as when the solution is
      minimal and elegant; or it can be derogatory, such as when the
      solution fixes the problem but leaves the system in an
      unmaintainable state.

      See [Raym] for several other meanings of this term and also
      definitions of several derivative terms.

   $ hacker
      1. (I) Someone with a strong interest in computers, who enjoys
      learning about them, programming them, and experimenting and
      otherwise working with them. (See: hack. Compare: adversary,
      cracker, intruder.)

      Usage: This first definition is the original meaning of the term
      (circa 1960); it then had a neutral or positive connotation of
      "someone who figures things out and makes something cool happen".

      2. (O) "An individual who spends an inordinate amount of time
      working on computer systems for other than professional purposes."
      [NCSSG]

      3. (D) Synonym for "cracker".

      Deprecated Usage: Today, the term is frequently (mis)used
      (especially by journalists) with definition 3.

   $ handle
      1. (I) /verb/ Perform processing operations on data, such as
      receive and transmit, collect and disseminate, create and delete,
      store and retrieve, read and write, and compare. (See: access.)

      2. (I) /noun/ An online pseudonym, particularly one used by a
      cracker; derived from citizens' band radio culture.

   $ handling restriction
      (I) A type of access control other than (a) the rule-based
      protections of mandatory access control and (b) the identity-based
      protections of discretionary access control; usually involves
      administrative security.

   $ Handling Restrictions field
      (I) A 16-bit field that specifies a control and release marking in
      the security option (option type 130) of IP's datagram header
      format. The valid field values are alphanumeric digraphs assigned
      by the U.S. Government, as specified in RFC 791.

      Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "H
      field" because it is potentially ambiguous. Instead, use "Handling
      Restrictions field".

   $ handshake
      (I) Protocol dialogue between two systems for identifying and
      authenticating themselves to each other, or for synchronizing
      their operations with each other.

   $ Handshake Protocol
      (I) /TLS/ The TLS Handshake Protocol consists of three parts
      (i.e., subprotocols) that enable peer entities to agree upon
      security parameters for the record layer, authenticate themselves
      to each other, instantiate negotiated security parameters, and
      report error conditions to each other. [R4346]

   $ harden
      (I) To protect a system by configuring it to operate in a way that
      eliminates or mitigates known vulnerabilities. Example: [RSCG].
      (See: default account.)

   $ hardware
      (I) The material physical components of an information system.
      (See: firmware, software.)

   $ hardware error
      (I) /threat action/ See: secondary definitions under "corruption",
      "exposure", and "incapacitation".

   $ hardware token
      See: token.

   $ hash code
      (D) Synonym for "hash result" or "hash function".

      Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
      in a potentially misleading way. A hash result is not a "code",
      and a hash function does not "encode" in any sense defined by this
      glossary. (See: hash value, message digest.)

   $ hash function
      1. (I) A function H that maps an arbitrary, variable-length bit
      string, s, into a fixed-length string, h = H(s) (called the "hash
      result"). For most computing applications, it is desirable that
      given a string s with H(s) = h, any change to s that creates a
      different string s' will result in an unpredictable hash result
      H(s') that is, with high probability, not equal to H(s).

      2. (O) "A (mathematical) function which maps values from a large
      (possibly very large) domain into a smaller range. A 'good' hash
      function is such that the results of applying the function to a
      (large) set of values in the domain will be evenly distributed
      (and apparently at random) over the range." [X509]

      Tutorial: A hash function operates on variable-length input (e.g.,
      a message or a file) and outputs a fixed-length output, which
      typically is much shorter than most input values. If the algorithm
      is "good" as described in the "O" definition, then the hash
      function may be a candidate for use in a security mechanism to
      detect accidental changes in data, but not necessarily for a
      mechanism to detect changes made by active wiretapping. (See:
      Tutorial under "checksum".)

      Security mechanisms require a "cryptographic hash function" (e.g.,
      MD2, MD4, MD5, SHA-1, Snefru), i.e., a good hash function that
      also has the one-way property and one of the two collision-free
      properties:
      -  "One-way property": Given H and a hash result h = H(s), it is
         hard (i.e., computationally infeasible, "impossible") to find
         s. (Of course, given H and an input s, it must be relatively
         easy to compute the hash result H(s).)
      -  "Weakly collision-free property": Given H and an input s, it is
         hard (i.e., computationally infeasible, "impossible") to find a
         different input, s', such that H(s) = H(s').
      -  "Strongly collision-free property": Given H, it is hard to find
         any pair of inputs s and s' such that H(s) = H(s').

      If H produces a hash result N bits long, then to find an s' where
      H(s') = H(s) for a specific given s, the amount of computation
      required is O(2**n); i.e., it is necessary to try on the order of
      2 to the power n values of s' before finding a collision. However,
      to simply find any pair of values s and s' that collide, the
      amount of computation required is only O(2**(n/2)); i.e., after
      computing H(s) for 2 to the power n/2 randomly chosen values of s,
      the probability is greater than 1/2 that two of those values have
      the same hash result. (See: birthday attack.)

   $ hash result
      1. (I) The output of a hash function. (See: hash code, hash value.
      Compare: hash value.)

      2. (O) "The output produced by a hash function upon processing a
      message" (where "message" is broadly defined as "a digital
      representation of data"). [DSG]

      Usage: IDOCs SHOULD avoid the unusual usage of "message" that is
      seen in the "O" definition.

   $ hash value
      (D) Synonym for "hash result".

      Deprecated Term: IDOCs SHOULD NOT use this term for the output of
      a hash function; the term could easily be confused with "hashed
      value", which means the input to a hash function. (See: hash code,
      hash result, message digest.)

   $ HDM
      (O) See: Hierarchical Development Methodology.

   $ Hierarchical Development Methodology (HDM)
      (O) A methodology, language, and integrated set of software tools
      developed at SRI International for specifying, coding, and
      verifying software to produce correct and reliable programs.
      [Cheh]

   $ hierarchical PKI
      (I) A PKI architecture based on a certification hierarchy.
      (Compare: mesh PKI, trust-file PKI.)

   $ hierarchy management
      (I) The process of generating configuration data and issuing
      public-key certificates to build and operate a certification
      hierarchy. (See: certificate management.)

   $ hierarchy of trust
      (D) Synonym for "certification hierarchy".

      Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
      in a potentially misleading way. (See: certification hierarchy,
      trust, web of trust.)

   $ high-assurance guard
      (O) "An oxymoron," said Lt. Gen. William H. Campbell, former U.S.
      Army chief information officer, speaking at an Armed Forces
      Communications and Electronics Association conference.

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the term mixes concepts and could easily be misunderstood.

   $ hijack attack
      (I) A form of active wiretapping in which the attacker seizes
      control of a previously established communication association.
      (See: man-in-the-middle attack, pagejacking, piggyback attack.)

   $ HIPAA
      (N) Health Information Portability and Accountability Act of 1996,
      a U.S. law (Public Law 104-191) that is intended to protect the
      privacy of patients' medical records and other health information
      in all forms, and mandates security for that information,
      including for its electronic storage and transmission.

   $ HMAC
      (I) A keyed hash [R2104] that can be based on any iterated
      cryptographic hash (e.g., MD5 or SHA-1), so that the cryptographic
      strength of HMAC depends on the properties of the selected
      cryptographic hash. (See: [R2202, R2403, R2404].)

      Derivation: Hash-based MAC. (Compare: CMAC.)

      Tutorial: Assume that H is a generic cryptographic hash in which a
      function is iterated on data blocks of length B bytes. L is the
      length of the of hash result of H. K is a secret key of length L
      <= K <= B. The values IPAD and OPAD are fixed strings used as
      inner and outer padding and defined as follows: IPAD = the byte
      0x36 repeated B times, and OPAD = the byte 0x5C repeated B times.
      HMAC is computed by H(K XOR OPAD, H(K XOR IPAD, inputdata)).

      HMAC has the following goals:
      -  To use available cryptographic hash functions without
         modification, particularly functions that perform well in
         software and for which software is freely and widely available.
      -  To preserve the original performance of the selected hash
         without significant degradation.
      -  To use and handle keys in a simple way.
      -  To have a well-understood cryptographic analysis of the
         strength of the mechanism based on reasonable assumptions about
         the underlying hash function.
      -  To enable easy replacement of the hash function in case a
         faster or stronger hash is found or required.

   $ honey pot
      (N) A system (e.g., a web server) or system resource (e.g., a file
      on a server) that is designed to be attractive to potential
      crackers and intruders, like honey is attractive to bears. (See:
      entrapment.)

      Usage: It is likely that other cultures use different metaphors
      for this concept. Therefore, to avoid international
      misunderstanding, an IDOC SHOULD NOT use this term without
      providing a definition for it. (See: Deprecated Usage under "Green
      Book".)

   $ host
      1. (I) /general/ A computer that is attached to a communication
      subnetwork or internetwork and can use services provided by the
      network to exchange data with other attached systems. (See: end
      system. Compare: server.)

      2. (I) /IPS/ A networked computer that does not forward IP packets
      that are not addressed to the computer itself. (Compare: router.)

      Derivation: As viewed by its users, a host "entertains" them,
      providing Application-Layer services or access to other computers
      attached to the network. However, even though some traditional
      peripheral service devices, such as printers, can now be

      independently connected to networks, they are not usually called
      hosts.

   $ HTML
      (I) See: Hypertext Markup Language.

   $ HTTP
      (I) See: Hypertext Transfer Protocol.

   $ https
      (I) When used in the first part of a URL (the part that precedes
      the colon and specifies an access scheme or protocol), this term
      specifies the use of HTTP enhanced by a security mechanism, which
      is usually SSL. (Compare: S-HTTP.)

   $ human error
      (I) /threat action/ See: secondary definitions under "corruption",
      "exposure", and "incapacitation".

   $ hybrid encryption
      (I) An application of cryptography that combines two or more
      encryption algorithms, particularly a combination of symmetric and
      asymmetric encryption. Examples: digital envelope, MSP, PEM, PGP.
      (Compare: superencryption.)

      Tutorial: Asymmetric algorithms require more computation than
      equivalently strong symmetric ones. Thus, asymmetric encryption is
      not normally used for data confidentiality except to distribute a
      symmetric key in a hybrid encryption scheme, where the symmetric
      key is usually very short (in terms of bits) compared to the data
      file it protects. (See: bulk key.)

   $ hyperlink
      (I) In hypertext or hypermedia, an information object (such as a
      word, a phrase, or an image, which usually is highlighted by color
      or underscoring) that points (i.e., indicates how to connect) to
      related information that is located elsewhere and can be retrieved
      by activating the link (e.g., by selecting the object with a mouse
      pointer and then clicking).

   $ hypermedia
      (I) A generalization of hypertext; any media that contain
      hyperlinks that point to material in the same or another data
      object.

   $ hypertext
      (I) A computer document, or part of a document, that contains
      hyperlinks to other documents; i.e., text that contains active
      pointers to other text. Usually written in HTML and accessed using
      a web browser. (See: hypermedia.)

   $ Hypertext Markup Language (HTML)
      (I) A platform-independent system of syntax and semantics (RFC
      1866) for adding characters to data files (particularly text
      files) to represent the data's structure and to point to related
      data, thus creating hypertext for use in the World Wide Web and
      other applications. (Compare: XML.)

   $ Hypertext Transfer Protocol (HTTP)
      (I) A TCP-based, Application-Layer, client-server, Internet
      protocol (RFC 2616) that is used to carry data requests and
      responses in the World Wide Web. (See: hypertext.)

   $ IAB
      (I) See: Internet Architecture Board.

   $ IANA
      (I) See: Internet Assigned Numbers Authority.

   $ IATF
      (O) See: Information Assurance Technical Framework.

   $ ICANN
      (I) See: Internet Corporation for Assigned Names and Numbers.

   $ ICMP
      (I) See: Internet Control Message Protocol.

   $ ICMP flood
      (I) A denial-of-service attack that sends a host more ICMP echo
      request ("ping") packets than the protocol implementation can
      handle. (See: flooding, smurf.)

   $ ICRL
      (N) See: indirect certificate revocation list.

   $ IDEA
      (N) See: International Data Encryption Algorithm.

   $ identification
      (I) An act or process that presents an identifier to a system so
      that the system can recognize a system entity and distinguish it
      from other entities. (See: authentication.)

   $ identification information
      (D) Synonym for "identifier"; synonym for "authentication
      information". (See: authentication, identifying information.)

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      either of those terms; this term (a) is not as precise as they are
      and (b) mixes concepts in a potentially misleading way. Instead,
      use "identifier" or "authentication information", depending on
      what is meant.

   $ Identification Protocol
      (I) A client-server Internet protocol [R1413] for learning the
      identity of a user of a particular TCP connection.

      Tutorial: Given a TCP port number pair, the server returns a
      character string that identifies the owner of that connection on
      the server's system. The protocol does not provide an
      authentication service and is not intended for authorization or
      access control. At best, it provides additional auditing
      information with respect to TCP.

   $ identifier
      (I) A data object -- often, a printable, non-blank character
      string -- that definitively represents a specific identity of a
      system entity, distinguishing that identity from all others.
      (Compare: identity.)

      Tutorial: Identifiers for system entities must be assigned very
      carefully, because authenticated identities are the basis for
      other security services, such as access control service.

   $ identifier credential
      1. (I) See: /authentication/ under "credential".

      2. (D) Synonym for "signature certificate".

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the term is used in many ways and could easily be
      misunderstood.

   $ identifying information
      (D) Synonym for "identifier"; synonym for "authentication
      information". (See: authentication, identification information.)

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      either of those terms; this term (a) is not as precise as they are
      and (b) mixes concepts in a potentially misleading way. Instead,

      use "identifier" or "authentication information", depending on
      what is meant.

   $ identity
      (I) The collective aspect of a set of attribute values (i.e., a
      set of characteristics) by which a system user or other system
      entity is recognizable or known. (See: authenticate, registration.
      Compare: identifier.)

      Usage: An IDOC MAY apply this term to either a single entity or a
      set of entities. If an IDOC involves both meanings, the IDOC
      SHOULD use the following terms and definitions to avoid ambiguity:
      -  "Singular identity": An identity that is registered for an
         entity that is one person or one process.
      -  "Shared identity": An identity that is registered for an entity
         that is a set of singular entities (1) in which each member is
         authorized to assume the identity individually and (2) for
         which the registering system maintains a record of the singular
         entities that comprise the set. In this case, we would expect
         each member entity to be registered with a singular identity
         before becoming associated with the shared identity.
      -  "Group identity": An identity that is registered for an entity
         (1) that is a set of entities (2) for which the registering
         system does not maintain a record of singular entities that
         comprise the set.

      Tutorial: When security services are based on identities, two
      properties are desirable for the set of attributes used to define
      identities:
      -  The set should be sufficient to distinguish each entity from
         all other entities, i.e., to represent each entity uniquely.
      -  The set should be sufficient to distinguish each identity from
         any other identities of the same entity.

      The second property is needed if a system permits an entity to
      register two or more concurrent identities. Having two or more
      identities for the same entity implies that the entity has two
      separate justifications for registration. In that case, the set of
      attributes used for identities must be sufficient to represent
      multiple identities for a single entity.

      Having two or more identities registered for the same entity is
      different from concurrently associating two different identifiers
      with the same identity, and also is different from a single
      identity concurrently accessing the system in two different roles.
      (See: principal, role-based access control.)

      When an identity of a user is being registered in a system, the
      system may require presentation of evidence that proves the
      identity's authenticity (i.e., that the user has the right to
      claim or use the identity) and its eligibility (i.e., that the
      identity is qualified to be registered and needs to be
      registered).

      The following diagram illustrates how this term relates to some
      other terms in a PKI system: authentication information,
      identifier, identifier credential, registration, registered user,
      subscriber, and user.

      Relationships:  === one-to-one, ==> one-to-many, <=> many-to-many.
                  +- - - - - - - - - - - - - - - - - - - - - - - - - - +
                  |                      PKI System                    |
      + - - - - + | +------------------+   +-------------------------+ |
      |  User,  | | |Subscriber, i.e., |   | Identity of Subscriber  | |
      |i.e., one| | | Registered User, |   |    is system-unique     | |
      | of the  | | | is system-unique |   | +---------------------+ | |
      |following| | | +--------------+ |   | |     Subscriber      | | |
      |         | | | | User's core  | |   | |     Identity's      | | |
      | +-----+ |===| | Registration | |==>| |  Registration data  | | |
      | |human| | | | | data, i.e.,  | |   | |+-------------------+| | |
      | |being| | | | | an entity's  | |   | ||  same core data   || | |
      | +-----+ | | | |distinguishing|========|for all Identities || | |
      |   or    | | | |  attribute   | |   | || of the same User  || | |
      | +-----+ | | | |   values     | | +===|+-------------------+| | |
      | |auto-| | | | +--------------+ | | | +---------------------+ | |
      | |mated| | | +------------------+ | +------------|------------+ |
      | |pro- | | |         |    +=======+              |              |
      | |cess | | | +-------v----|----------------------|------------+ |
      | +-----+ | | | +----------v---+     +------------v----------+ | |
      |   or    | | | |Authentication|<===>|Identifier of Identity | | |
      |+-------+| | | | Information  |     |    is system-unique   | | |
      || a set || | | +--------------+     +-----------------------+ | |
      ||  of   || | | Identifier Credential that associates unit of  | |
      || either|| | | Authentication Information with the Identifier | |
      |+-------+| | +------------------------------------------------+ |
      + - - - - + + - - - - - - - - - - - - - - - - - - - - - - - - - -+

   $ identity-based security policy
      (I) "A security policy based on the identities and/or attributes
      of users, a group of users, or entities acting on behalf of the
      users and the resources/objects being accessed." [I7498-2] (See:
      rule-based security policy.)

   $ identity proofing
      (I) A process that vets and verifies the information that is used
      to establish the identity of a system entity. (See: registration.)

   $ IDOC
      (I) An abbreviation used in this Glossary to refer to a document
      or other item of written material that is generated in the
      Internet Standards Process (RFC 2026), i.e., an RFC, an Internet-
      Draft, or some other item of discourse.

      Deprecated Usage: This abbreviation SHOULD NOT be used in an IDOC
      unless it is first defined in the IDOC because the abbreviation
      was invented for this Glossary and is not widely known.

   $ IDS
      (I) See: intrusion detection system.

   $ IEEE
      (N) See: Institute of Electrical and Electronics Engineers, Inc.

   $ IEEE 802.10
      (N) An IEEE committee developing security standards for LANs.
      (See: SILS.)

   $ IEEE P1363
      (N) An IEEE working group, Standard for Public-Key Cryptography,
      engaged in developing a comprehensive reference standard for
      asymmetric cryptography. Covers discrete logarithm (e.g., DSA),
      elliptic curve, and integer factorization (e.g., RSA); and covers
      key agreement, digital signature, and encryption.

   $ IESG
      (I) See: Internet Engineering Steering Group.

   $ IETF
      (I) See: Internet Engineering Task Force.

   $ IKE
      (I) See: IPsec Key Exchange.

   $ IMAP4
      (I) See: Internet Message Access Protocol, version 4.

   $ IMAP4 AUTHENTICATE
      (I) An IMAP4 command (better described as a transaction type, or
      subprotocol) by which an IMAP4 client optionally proposes a
      mechanism to an IMAP4 server to authenticate the client to the
      server and provide other security services. (See: POP3.)

      Tutorial: If the server accepts the proposal, the command is
      followed by performing a challenge-response authentication
      protocol and, optionally, negotiating a protection mechanism for
      subsequent POP3 interactions. The security mechanisms that are
      used by IMAP4 AUTHENTICATE -- including Kerberos, GSS-API, and
      S/Key -- are described in [R1731].

   $ impossible
      (O) Cannot be done in any reasonable amount of time. (See: break,
      brute force, strength, work factor.)

   $ in the clear
      (I) Not encrypted. (See: clear text.)

   $ Ina Jo
      (O) A methodology, language, and integrated set of software tools
      developed at the System Development Corporation for specifying,
      coding, and verifying software to produce correct and reliable
      programs. Usage: a.k.a. the Formal Development Methodology. [Cheh]

   $ incapacitation
      (I) A type of threat action that prevents or interrupts system
      operation by disabling a system component. (See: disruption.)

      Usage: This type of threat action includes the following subtypes:
      -  "Malicious logic": In context of incapacitation, any hardware,
         firmware, or software (e.g., logic bomb) intentionally
         introduced into a system to destroy system functions or
         resources. (See: corruption, main entry for "malicious logic",
         masquerade, misuse.)
      -  "Physical destruction": Deliberate destruction of a system
         component to interrupt or prevent system operation.
      -  "Human error": /incapacitation/ Action or inaction that
         unintentionally disables a system component. (See: corruption,
         exposure.)
      -  "Hardware or software error": /incapacitation/ Error that
         unintentionally causes failure of a system component and leads
         to disruption of system operation. (See: corruption, exposure.)
      -  "Natural disaster": /incapacitation/ Any "act of God" (e.g.,
         fire, flood, earthquake, lightning, or wind) that disables a
         system component. [FP031 Section 2]

   $ incident
      See: security incident.

   $ INCITS
      (N) See: "International Committee for Information Technology
      Standardization" under "ANSI".

   $ indicator
      (N) An action -- either specific, generalized, or theoretical --
      that an adversary might be expected to take in preparation for an
      attack. [C4009] (See: "attack sensing, warning, and response".
      Compare: message indicator.)

   $ indirect attack
      (I) See: secondary definition under "attack". Compare: direct
      attack.

   $ indirect certificate revocation list (ICRL)
      (N) In X.509, a CRL that may contain certificate revocation
      notifications for certificates issued by CAs other than the issuer
      (i.e., signer) of the ICRL.

   $ indistinguishability
      (I) An attribute of an encryption algorithm that is a
      formalization of the notion that the encryption of some string is
      indistinguishable from the encryption of an equal-length string of
      nonsense. (Compare: semantic security.)

   $ inference
      1. (I) A type of threat action that reasons from characteristics
      or byproducts of communication and thereby indirectly accesses
      sensitive data, but not necessarily the data contained in the
      communication. (See: traffic analysis, signal analysis.)

      2. (I) A type of threat action that indirectly gains unauthorized
      access to sensitive information in a database management system by
      correlating query responses with information that is already
      known.

   $ inference control
      (I) Protection of data confidentiality against inference attack.
      (See: traffic-flow confidentiality.)

      Tutorial: A database management system containing N records about
      individuals may be required to provide statistical summaries about
      subsets of the population, while not revealing sensitive
      information about a single individual. An attacker may try to
      obtain sensitive information about an individual by isolating a
      desired record at the intersection of a set of overlapping
      queries. A system can attempt to prevent this by restricting the
      size and overlap of query sets, distorting responses by rounding
      or otherwise perturbing database values, and limiting queries to
      random samples. However, these techniques may be impractical to
      implement or use, and no technique is totally effective. For
      example, restricting the minimum size of a query set -- that is,

      not responding to queries for which there are fewer than K or more
      than N-K records that satisfy the query -- usually cannot prevent
      unauthorized disclosure. An attacker can pad small query sets with
      extra records, and then remove the effect of the extra records.
      The formula for identifying the extra records is called the
      "tracker". [Denns]

   $ INFOCON
      (O) See: information operations condition

   $ informal
      (N) Expressed in natural language. [CCIB] (Compare: formal,
      semiformal.)

   $ information
      1. (I) Facts and ideas, which can be represented (encoded) as
      various forms of data.

      2. (I) Knowledge -- e.g., data, instructions -- in any medium or
      form that can be communicated between system entities.

      Tutorial: Internet security could be defined simply as protecting
      information in the Internet. However, the perceived need to use
      different protective measures for different types of information
      (e.g., authentication information, classified information,
      collateral information, national security information, personal
      information, protocol control information, sensitive compartmented
      information, sensitive information) has led to the diversity of
      terminology listed in this Glossary.

   $ information assurance
      (N) /U.S. Government/ "Measures that protect and defend
      information and information systems by ensuring their availability
      integrity, authentication, confidentiality, and non-repudiation.
      These measures include providing for restoration of information
      systems by incorporating protection, detection, and reaction
      capabilities." [C4009]

   $ Information Assurance Technical Framework (IATF)
      (O) A publicly available document [IATF], developed through a
      collaborative effort by organizations in the U.S. Government and
      industry, and issued by NSA. Intended for security managers and
      system security engineers as a tutorial and reference document
      about security problems in information systems and networks, to
      improve awareness of tradeoffs among available technology
      solutions and of desired characteristics of security approaches
      for particular problems. (See: ISO 17799, [SP14].)

   $ information domain
      (O) See: secondary definition under "domain".

   $ information domain security policy
      (O) See: secondary definition under "domain".

   $ information flow policy
      (N) /formal model/ A triple consisting of a set of security levels
      (or their equivalent security labels), a binary operator that maps
      each pair of security levels into a security level, and a binary
      relation on the set that selects a set of pairs of levels such
      that information is permitted to flow from an object of the first
      level to an object of the second level. (See: flow control,
      lattice model.)

   $ information operations condition (INFOCON)
      (O) /U.S. DoD/ A comprehensive defense posture and response based
      on the status of information systems, military operations, and
      intelligence assessments of adversary capabilities and intent.
      (See: threat)

      Derivation: From DEFCON, i.e., defense condition.

      Tutorial: The U.S. DoD defines five INFOCON levels: NORMAL (normal
      activity), ALPHA (increased risk of attack), BRAVO (specific risk
      of attack), CHARLIE (limited attack), and DELTA (general attack).

   $ information security (INFOSEC)
      (N) Measures that implement and assure security services in
      information systems, including in computer systems (see: COMPUSEC)
      and in communication systems (see: COMSEC).

   $ information system
      (I) An organized assembly of computing and communication resources
      and procedures -- i.e., equipment and services, together with
      their supporting infrastructure, facilities, and personnel -- that
      create, collect, record, process, store, transport, retrieve,
      display, disseminate, control, or dispose of information to
      accomplish a specified set of functions. (See: system entity,
      system resource. Compare: computer platform.)

   $ Information Technology Security Evaluation Criteria (ITSEC)
      (N) A Standard [ITSEC] jointly developed by France, Germany, the
      Netherlands, and the United Kingdom for use in the European Union;
      accommodates a wider range of security assurance and functionality
      combinations than the TCSEC. Superseded by the Common Criteria.

   $ INFOSEC
      (I) See: information security.

   $ ingress filtering
      (I) A method [R2827] for countering attacks that use packets with
      false IP source addresses, by blocking such packets at the
      boundary between connected networks.

      Tutorial: Suppose network A of an internet service provider (ISP)
      includes a filtering router that is connected to customer network
      B, and an attacker in B at IP source address "foo" attempts to
      send packets with false source address "bar" into A. The false
      address may be either fixed or randomly changing, and it may
      either be unreachable or be a forged address that legitimately
      exists within either B or some other network C. In ingress
      filtering, the ISP's router blocks all inbound packet that arrive
      from B with a source address that is not within the range of
      legitimately advertised addresses for B. This method does not
      prevent all attacks that can originate from B, but the actual
      source of such attacks can be more easily traced because the
      originating network is known.

   $ initialization value (IV)
      (I) /cryptography/ An input parameter that sets the starting state
      of a cryptographic algorithm or mode. (Compare: activation data.)

      Tutorial: An IV can be used to synchronize one cryptographic
      process with another; e.g., CBC, CFB, and OFB use IVs. An IV also
      can be used to introduce cryptographic variance (see: salt)
      besides that provided by a key.

   $ initialization vector
      (D) /cryptography/ Synonym for "initialization value".

      Deprecated Term: To avoid international misunderstanding, IDOCs
      SHOULD NOT use this term in the context of cryptography because
      most dictionary definitions of "vector" includes a concept of
      direction or magnitude, which are irrelevant to cryptographic use.

   $ insertion
      1. (I) /packet/ See: secondary definition under "stream integrity
      service".

      2. (I) /threat action/ See: secondary definition under
      "falsification".

   $ inside attack
      (I) See: secondary definition under "attack". Compare: insider.

   $ insider
      1. (I) A user (usually a person) that accesses a system from a
      position that is inside the system's security perimeter. (Compare:
      authorized user, outsider, unauthorized user.)

      Tutorial: An insider has been assigned a role that has more
      privileges to access system resources than do some other types of
      users, or can access those resources without being constrained by
      some access controls that are applied to outside users. For
      example, a salesclerk is an insider who has access to the cash
      register, but a store customer is an outsider.

      The actions performed by an insider in accessing the system may be
      either authorized or unauthorized; i.e., an insider may act either
      as an authorized user or as an unauthorized user.

      2. (O) A person with authorized physical access to the system.
      Example: In this sense, an office janitor is an insider, but a
      burglar or casual visitor is not. [NRC98]

      3. (O) A person with an organizational status that causes the
      system or members of the organization to view access requests as
      being authorized. Example: In this sense, a purchasing agent is an
      insider but a vendor is not. [NRC98]

   $ inspectable space
      (O) /EMSEC/ "Three-dimensional space surrounding equipment that
      process classified and/or sensitive information within which
      TEMPEST exploitation is not considered practical or where legal
      authority to identify and/or remove a potential TEMPEST
      exploitation exists." [C4009] (Compare: control zone, TEMPEST
      zone.)

   $ Institute of Electrical and Electronics Engineers, Inc. (IEEE)
      (N) The IEEE is a not-for-profit association of approximately
      300,000 individual members in 150 countries. The IEEE produces
      nearly one third of the world's published literature in electrical
      engineering, computers, and control technology; holds hundreds of
      major, annual conferences; and maintains more than 800 active
      standards, with many more under development. (See: SILS.)

   $ integrity
      See: data integrity, datagram integrity service, correctness
      integrity, source integrity, stream integrity service, system
      integrity.

   $ integrity check
      (D) A computation that is part of a mechanism to provide data
      integrity service or data origin authentication service. (Compare:
      checksum.)

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "cryptographic hash" or "protected checksum". This term
      unnecessarily duplicates the meaning of other, well-established
      terms; this term only mentions integrity, even though the intended
      service may be data origin authentication; and not every checksum
      is cryptographically protected.

   $ integrity label
      (I) A security label that tells the degree of confidence that may
      be placed in the data, and may also tell what countermeasures are
      required to be applied to protect the data from alteration and
      destruction. (See: integrity. Compare: classification label.)

   $ intelligent threat
      (I) A circumstance in which an adversary has the technical and
      operational ability to detect and exploit a vulnerability and also
      has the demonstrated, presumed, or inferred intent to do so. (See:
      threat.)

   $ interception
      (I) A type of threat action whereby an unauthorized entity
      directly accesses sensitive data while the data is traveling
      between authorized sources and destinations. (See: unauthorized
      disclosure.)

      Usage: This type of threat action includes the following subtypes:
      -  "Theft": Gaining access to sensitive data by stealing a
         shipment of a physical medium, such as a magnetic tape or disk,
         that holds the data.
      -  "Wiretapping (passive)": Monitoring and recording data that is
         flowing between two points in a communication system. (See:
         wiretapping.)
      -  "Emanations analysis": Gaining direct knowledge of communicated
         data by monitoring and resolving a signal that is emitted by a
         system and that contains the data but was not intended to
         communicate the data. (See: emanation.)

   $ interference
      (I) /threat action/ See: secondary definition under "obstruction".

   $ intermediate CA
      (D) The CA that issues a cross-certificate to another CA. [X509]
      (See: cross-certification.)

      Deprecated Term: IDOCs SHOULD NOT use this term because it is not
      widely known and mixes concepts in a potentially misleading way.
      For example, suppose that end entity 1 ("EE1) is in one PKI
      ("PKI1"), end entity 2 ("EE2) is in another PKI ("PKI2"), and the
      root in PKI1 ("CA1") cross-certifies the root CA in PKI2 ("CA2").
      Then, if EE1 constructs the certification path CA1-to-CA2-to-EE2
      to validate a certificate of EE2, conventional English usage would
      describe CA2 as being in the "intermediate" position in that path,
      not CA1.

   $ internal controls
      (I) /COMPUSEC/ Functions, features, and technical characteristics
      of computer hardware and software, especially of operating
      systems. Includes mechanisms to regulate the operation of a
      computer system with regard to access control, flow control, and
      inference control. (Compare: external controls.)

   $ International Data Encryption Algorithm (IDEA)
      (N) A patented, symmetric block cipher that uses a 128-bit key and
      operates on 64-bit blocks. [Schn] (See: symmetric cryptography.)

   $ International Standard
      (N) See: secondary definition under "ISO".

   $ International Traffic in Arms Regulations (ITAR)
      (O) Rules issued by the U.S. State Department, by authority of the
      Arms Export Control Act (22 U.S.C. 2778), to control export and
      import of defense articles and defense services, including
      information security systems, such as cryptographic systems, and
      TEMPEST suppression technology. (See: type 1 product, Wassenaar
      Arrangement.)

   $ internet, Internet
      1. (I) /not capitalized/ Abbreviation of "internetwork".

      2. (I) /capitalized/ The Internet is the single, interconnected,
      worldwide system of commercial, governmental, educational, and
      other computer networks that share (a) the protocol suite
      specified by the IAB (RFC 2026) and (b) the name and address
      spaces managed by the ICANN. (See: Internet Layer, Internet
      Protocol Suite.)

      Usage: Use with definite article ("the") when using as a noun. For
      example, say "My LAN is small, but the Internet is large." Don't
      say "My LAN is small, but Internet is large."

   $ Internet Architecture Board (IAB)
      (I) A technical advisory group of the ISOC, chartered by the ISOC
      Trustees to provide oversight of Internet architecture and
      protocols and, in the context of Internet Standards, a body to
      which decisions of the IESG may be appealed. Responsible for
      approving appointments to the IESG from among nominees submitted
      by the IETF nominating committee. (RFC 2026)

   $ Internet Assigned Numbers Authority (IANA)
      (I) From the early days of the Internet, the IANA was chartered by
      the ISOC and the U.S. Government's Federal Network Council to be
      the central coordination, allocation, and registration body for
      parameters for Internet protocols. Superseded by ICANN.

   $ Internet Control Message Protocol (ICMP)
      (I) An Internet Standard protocol (RFC 792) that is used to report
      error conditions during IP datagram processing and to exchange
      other information concerning the state of the IP network.

   $ Internet Corporation for Assigned Names and Numbers (ICANN)
      (I) The non-profit, private corporation that has assumed
      responsibility for the IP address space allocation, protocol
      parameter assignment, DNS management, and root server system
      management functions formerly performed under U.S. Government
      contract by IANA and other entities.

      Tutorial: The IPS, as defined by the IETF and the IESG, contains
      numerous parameters, such as Internet addresses, domain names,
      autonomous system numbers, protocol numbers, port numbers,
      management information base OIDs, including private enterprise
      numbers, and many others. The Internet community requires that the
      values used in these parameter fields be assigned uniquely. ICANN
      makes those assignments as requested and maintains a registry of
      the current values.

      ICANN was formed in October 1998, by a coalition of the Internet's
      business, technical, and academic communities. The U.S. Government
      designated ICANN to serve as the global consensus entity with
      responsibility for coordinating four key functions for the
      Internet: allocation of IP address space, assignment of protocol
      parameters, management of the DNS, and management of the DNS root
      server system.

   $ Internet-Draft
      (I) A working document of the IETF, its areas, and its working
      groups. (RFC 2026) (Compare: RFC.)

      Usage: The term is customarily hyphenated when used either as a
      adjective or a noun, even though the latter is not standard
      English punctuation.

      Tutorial: An Internet-Draft is not an archival document like an
      RFC is. Instead, an Internet-Draft is a preliminary or working
      document that is valid for a maximum of six months and may be
      updated, replaced, or made obsolete by other documents at any
      time. It is inappropriate to use an Internet-Draft as reference
      material or to cite it other than as a "work in progress".
      Although most of the Internet-Drafts are produced by the IETF, any
      interested organization may request to have its working documents
      published as Internet-Drafts.

   $ Internet Engineering Steering Group (IESG)
      (I) The part of the ISOC responsible for technical management of
      IETF activities and administration of the Internet Standards
      Process according to procedures approved by the ISOC Trustees.
      Directly responsible for actions along the "standards track",
      including final approval of specifications as Internet Standards.
      Composed of IETF Area Directors and the IETF chairperson, who also
      chairs the IESG. (RFC 2026)

   $ Internet Engineering Task Force (IETF)
      (I) A self-organized group of people who make contributions to the
      development of Internet technology. The principal body engaged in
      developing Internet Standards, although not itself a part of the
      ISOC. Composed of Working Groups, which are arranged into Areas
      (such as the Security Area), each coordinated by one or more Area
      Directors. Nominations to the IAB and the IESG are made by a
      committee selected at random from regular IETF meeting attendees
      who have volunteered. (RFCs 2026, 3935) [R2323]

   $ Internet Key Exchange (IKE)
      (I) An Internet, IPsec, key-establishment protocol [R4306] for
      putting in place authenticated keying material (a) for use with
      ISAKMP and (b) for other security associations, such as in AH and
      ESP.

      Tutorial: IKE is based on three earlier protocol designs: ISAKMP,
      OAKLEY, and SKEME.

   $ Internet Layer
      (I) See: Internet Protocol Suite.

   $ Internet Message Access Protocol, version 4 (IMAP4)
      (I) An Internet protocol (RFC 2060) by which a client workstation
      can dynamically access a mailbox on a server host to manipulate

      and retrieve mail messages that the server has received and is
      holding for the client. (See: POP3.)

      Tutorial: IMAP4 has mechanisms for optionally authenticating a
      client to a server and providing other security services. (See:
      IMAP4 AUTHENTICATE.)

   $ Internet Open Trading Protocol (IOTP)
      (I) An Internet protocol [R2801] proposed as a general framework
      for Internet commerce, able to encapsulate transactions of various
      proprietary payment systems (e.g., GeldKarte, Mondex, SET, Visa
      Cash). Provides optional security services by incorporating
      various Internet security mechanisms (e.g., MD5) and protocols
      (e.g., TLS).

   $ Internet Policy Registration Authority (IPRA)
      (I) An X.509-compliant CA that is the top CA of the Internet
      certification hierarchy operated under the auspices of the ISOC
      [R1422]. (See: /PEM/ under "certification hierarchy".)

   $ Internet Private Line Interface (IPLI)
      (O) A successor to the PLI, updated to use TCP/IP and newer
      military-grade COMSEC equipment (TSEC/KG-84). The IPLI was a
      portable, modular system that was developed for use in tactical,
      packet-radio networks. (See: end-to-end encryption.)

   $ Internet Protocol (IP)
      (I) An Internet Standard, Internet-Layer protocol that moves
      datagrams (discrete sets of bits) from one computer to another
      across an internetwork but does not provide reliable delivery,
      flow control, sequencing, or other end-to-end services that TCP
      provides. IP version 4 (IPv4) is specified in RFC 791, and IP
      version 6 (IPv6) is specified in RFC 2460. (See: IP address,
      TCP/IP.)

      Tutorial: If IP were used in an OSIRM stack, IP would be placed at
      the top of Layer 3, above other Layer 3 protocols in the stack.

      In any IPS stack, IP is always present in the Internet Layer and
      is always placed at the top of that layer, on top of any other
      protocols that are used in that layer. In some sense, IP is the
      only protocol specified for the IPS Internet Layer; other
      protocols used there, such as AH and ESP, are just IP variations.

   $ Internet Protocol security
      See: IP Security Protocol.

   $ Internet Protocol Security Option (IPSO)
      (I) Refers to one of three types of IP security options, which are
      fields that may be added to an IP datagram for carrying security
      information about the datagram. (Compare: IPsec.)

      Deprecated Usage: IDOCs SHOULD NOT use this term without a
      modifier to indicate which of the following three types is meant:
      -  "DoD Basic Security Option" (IP option type 130): Defined for
         use on U.S. DoD common-use data networks. Identifies the DoD
         classification level at which the datagram is to be protected
         and the protection authorities whose rules apply to the
         datagram. (A "protection authority" is a National Access
         Program (e.g., GENSER, SIOP-ESI, SCI, NSA, Department of
         Energy) or Special Access Program that specifies protection
         rules for transmission and processing of the information
         contained in the datagram.) [R1108]
      -  "DoD Extended Security Option" (IP option type 133): Permits
         additional security labeling information, beyond that present
         in the Basic Security Option, to be supplied in the datagram to
         meet the needs of registered authorities. [R1108]
      -  "Common IP Security Option" (CIPSO) (IP option type 134):
         Designed by TSIG to carry hierarchic and non-hierarchic
         security labels. (Formerly called "Commercial IP Security
         Option"; a version 2.3 draft was published 9 March 1993 as an
         Internet-Draft but did not advance to RFC form.) [CIPSO]

   $ Internet Protocol Suite (IPS)
      (I) The set of network communication protocols that are specified
      by the IETF, and approved as Internet Standards by the IESG,
      within the oversight of the IAB. (See: OSIRM Security
      Architecture. Compare: OSIRM.)

      Usage: This set of protocols is popularly known as "TCP/IP"
      because TCP and IP are its most basic and important components.

      For clarity, this Glossary refers to IPS protocol layers by name
      and capitalizes those names, and refers to OSIRM protocol layers
      by number.

      Tutorial: The IPS does have architectural principles [R1958], but
      there is no Internet Standard that defines a layered IPS reference
      model like the OSIRM. Still, Internet community literature has
      referred (inconsistently) to IPS layers since early in the
      Internet's development [Padl].

      This Glossary treats the IPS as having five protocol layers --
      Application, Transport, Internet, Network Interface, and Network
      Hardware (or Network Substrate) -- which are illustrated in the
      following diagram:

      OSIRM Layers       Examples          IPS Layers     Examples
      ------------------ ---------------  --------------- --------------
      Message Format:    P2   [X420]      Message Format: ARPA (RFC 822)
      +----------------+                  +-------------+
      |7.Application   | P1   [X419]      | Application | SMTP (RFC 821)
      +----------------+ -  -  -  -  -  - |             |
      |6.Presentation  |      [I8823]     |             |
      +----------------+ -  -  -  -  -  - |             |
      |5.Session       |      [I8327]     +-------------+
      +----------------+ -  -  -  -  -  - |  Transport  | TCP  (RFC 793)
      |4.Transport     | TP4  [I8073]     |             |
      +----------------+ -  -  -  -  -  - +-------------+
      |3.Network       | CLNP [I8473]     |  Internet   | IP   (RFC 791)
      |                |                  +-------------+
      |                |                  |   Network   | IP over IEEE
      +----------------+ -  -  -  -  -  - |  Interface  | 802 (RFC 1042)
      |2.Data Link     |                  +-------------+
      |                | LLC  [I8802-2]   -   Network   - The IPS does
      |                | MAC  [I8802-3]   -  Hardware   - not include
      +----------------+                  - (or Network - standards for
      |1.Physical      | Baseband         -  Substrate) - this layer.
      +----------------+ Signaling [Stal] + - - - - - - +

      The diagram approximates how the five IPS layers align with the
      seven OSIRM layers, and it offers examples of protocol stacks that
      provide roughly equivalent electronic mail service over a private
      LAN that uses baseband signaling.

      -  IPS Application Layer: The user runs an application program.
         The program selects the data transport service it needs --
         either a sequence of data messages or a continuous stream of
         data -- and hands application data to the Transport Layer for
         delivery.

      -  IPS Transport Layer: This layer divides application data into
         packets, adds a destination address to each, and communicates
         them end-to-end -- from one application program to another --
         optionally regulating the flow and ensuring reliable (error-
         free and sequenced) delivery.

      -  IPS Internet Layer: This layer carries transport packets in IP
         datagrams. It moves each datagram independently, from its
         source computer to its addressed destination computer, routing

         the datagram through a sequence of networks and relays and
         selecting appropriate network interfaces en route.

      -  IPS Network Interface Layer: This layer accepts datagrams for
         transmission over a specific network. This layer specifies
         interface conventions for carrying IP over OSIRM Layer 3
         protocols and over Media Access Control sublayer protocols of
         OSIRM Layer 2. An example is IP over IEEE 802 (RFD 1042).

      -  IPS Network Hardware Layer: This layer consists of specific,
         physical communication media. However, the IPS does not specify
         its own peer-to-peer protocols in this layer. Instead, the
         layering conventions specified by the Network Interface Layer
         use Layer 2 and Layer 3 protocols that are specified by bodies
         other than the IETF. That is, the IPS addresses *inter*-network
         functions and does not address *intra*-network functions.

      The two models are most dissimilar in the upper layers, where the
      IPS model does not include Session and Presentation layers.
      However, this omission causes fewer functional differences between
      the models than might be imagined, and the differences have
      relatively few security implications:

      -  Formal separation of OSIRM Layers 5, 6, and 7 is not needed in
         implementations; the functions of these layers sometimes are
         mixed in a single software unit, even in protocols in the OSI
         suite.

      -  Some OSIRM Layer 5 services -- for example, connection
         termination -- are built into TCP, and the remaining Layer 5
         and 6 functions are built into IPS Application-Layer protocols
         where needed.

      -  The OSIRM does not place any security services in Layer 5 (see:
         OSIRM Security Architecture).

      -  The lack of an explicit Presentation Layer in the IPS sometimes
         makes it simpler to implement security in IPS applications. For
         example, a primary function of Layer 6 is to convert data
         between internal and external forms, using a transfer syntax to
         unambiguously encode data for transmission. If an OSIRM
         application encrypts data to protect against disclosure during
         transmission, the transfer encoding must be done before the
         encryption. If an application does encryption, as is done in
         OSI message handling and directory service protocols, then
         Layer 6 functions must be replicated in Layer 7. [X400, X500].

      The two models are most alike at the top of OSIRM Layer 3, where
      the OSI Connectionless Network Layer Protocol (CLNP) and the IPS
      IP are quite similar. Connection-oriented security services
      offered in OSIRM Layer 3 are inapplicable in the IPS, because the
      IPS Internet Layer lacks the explicit, connection-oriented service
      offered in the OSIRM.

   $ Internet Security Association and Key Management Protocol (ISAKMP)
      (I) An Internet IPsec protocol [R2408] to negotiate, establish,
      modify, and delete security associations, and to exchange key
      generation and authentication data, independent of the details of
      any specific key generation technique, key establishment protocol,
      encryption algorithm, or authentication mechanism.

      Tutorial: ISAKMP supports negotiation of security associations for
      protocols at all IPS layers. By centralizing management of
      security associations, ISAKMP reduces duplicated functionality
      within each protocol. ISAKMP can also reduce connection setup
      time, by negotiating a whole stack of services at once. Strong
      authentication is required on ISAKMP exchanges, and a digital
      signature algorithm based on asymmetric cryptography is used
      within ISAKMP's authentication component.

      ISAKMP negotiations are conducted in two "phases":
      -  "Phase 1 negotiation". A phase 1 negotiation establishes a
         security association to be used by ISAKMP to protect its own
         protocol operations.
      -  "Phase 2 negotiation". A phase 2 negotiation (which is
         protected by a security association that was established by a
         phase 1 negotiation) establishes a security association to be
         used to protect the operations of a protocol other than ISAKMP,
         such as ESP.

   $ Internet Society (ISOC)
      (I) A professional society concerned with Internet development
      (including technical Internet Standards); with how the Internet is
      and can be used; and with social, political, and technical issues
      that result. The ISOC Board of Trustees approves appointments to
      the IAB from among nominees submitted by the IETF nominating
      committee. (RFC 2026)

   $ Internet Standard
      (I) A specification, approved by the IESG and published as an RFC,
      that is stable and well-understood, is technically competent, has
      multiple, independent, and interoperable implementations with
      substantial operational experience, enjoys significant public
      support, and is recognizably useful in some or all parts of the
      Internet. (RFC 2026) (Compare: RFC.)

      Tutorial: The "Internet Standards Process" is an activity of the
      ISOC and is organized and managed by the IAB and the IESG. The
      process is concerned with all protocols, procedures, and
      conventions used in or by the Internet, whether or not they are
      part of the IPS. The "Internet Standards Track" has three levels
      of increasing maturity: Proposed Standard, Draft Standard, and
      Standard. (Compare: ISO, W3C.)

   $ internetwork
      (I) A system of interconnected networks; a network of networks.
      Usually shortened to "internet". (See: internet, Internet.)

      Tutorial: An internet can be built using OSIRM Layer 3 gateways to
      implement connections between a set of similar subnetworks. With
      dissimilar subnetworks, i.e., subnetworks that differ in the Layer
      3 protocol service they offer, an internet can be built by
      implementing a uniform internetwork protocol (e.g., IP) that
      operates at the top of Layer 3 and hides the underlying
      subnetworks' heterogeneity from hosts that use communication
      services provided by the internet. (See: router.)

   $ intranet
      (I) A computer network, especially one based on Internet
      technology, that an organization uses for its own internal (and
      usually private) purposes and that is closed to outsiders. (See:
      extranet, VPN.)

   $ intruder
      (I) An entity that gains or attempts to gain access to a system or
      system resource without having authorization to do so. (See:
      intrusion. Compare: adversary, cracker, hacker.)

   $ intrusion
      1. (I) A security event, or a combination of multiple security
      events, that constitutes a security incident in which an intruder
      gains, or attempts to gain, access to a system or system resource
      without having authorization to do so. (See: IDS.)

      2. (I) A type of threat action whereby an unauthorized entity
      gains access to sensitive data by circumventing a system's
      security protections. (See: unauthorized disclosure.)

      Usage: This type of threat action includes the following subtypes:
      -  "Trespass": Gaining physical access to sensitive data by
         circumventing a system's protections.
      -  "Penetration": Gaining logical access to sensitive data by
         circumventing a system's protections.

      -  "Reverse engineering": Acquiring sensitive data by
         disassembling and analyzing the design of a system component.
      -  "Cryptanalysis": Transforming encrypted data into plain text
         without having prior knowledge of encryption parameters or
         processes. (See: main entry for "cryptanalysis".)

   $ intrusion detection
      (I) Sensing and analyzing system events for the purpose of
      noticing (i.e., becoming aware of) attempts to access system
      resources in an unauthorized manner. (See: anomaly detection, IDS,
      misuse detection. Compare: extrusion detection.) [IDSAN, IDSSC,
      IDSSE, IDSSY]

      Usage: This includes the following subtypes:
      -  "Active detection": Real-time or near-real-time analysis of
         system event data to detect current intrusions, which result in
         an immediate protective response.
      -  "Passive detection": Off-line analysis of audit data to detect
         past intrusions, which are reported to the system security
         officer for corrective action. (Compare: security audit.)

   $ intrusion detection system (IDS)
      1. (N) A process or subsystem, implemented in software or
      hardware, that automates the tasks of (a) monitoring events that
      occur in a computer network and (b) analyzing them for signs of
      security problems. [SP31] (See: intrusion detection.)

      2. (N) A security alarm system to detect unauthorized entry.
      [DC6/9].

      Tutorial: Active intrusion detection processes can be either host-
      based or network-based:
      -  "Host-based": Intrusion detection components -- traffic sensors
         and analyzers -- run directly on the hosts that they are
         intended to protect.
      -  "Network-based": Sensors are placed on subnetwork components,
         and analysis components run either on subnetwork components or
         hosts.

   $ invalidity date
      (N) An X.509 CRL entry extension that "indicates the date at which
      it is known or suspected that the [revoked certificate's private
      key] was compromised or that the certificate should otherwise be
      considered invalid." [X509].

      Tutorial: This date may be earlier than the revocation date in the
      CRL entry, and may even be earlier than the date of issue of
      earlier CRLs. However, the invalidity date is not, by itself,

      sufficient for purposes of non-repudiation service. For example,
      to fraudulently repudiate a validly generated signature, a private
      key holder may falsely claim that the key was compromised at some
      time in the past.

   $ IOTP
      (I) See: Internet Open Trading Protocol.

   $ IP
      (I) See: Internet Protocol.

   $ IP address
      (I) A computer's internetwork address that is assigned for use by
      IP and other protocols.

      Tutorial: An IP version 4 address (RFC 791) has four 8-bit parts
      and is written as a series of four decimal numbers separated by
      periods. Example: The address of the host named "rosslyn.bbn.com"
      is 192.1.7.10.

      An IP version 6 address (RFC 2373) has eight 16-bit parts and is
      written as eight hexadecimal numbers separated by colons.
      Examples: 1080:0:0:0:8:800:200C:417A and
      FEDC:BA98:7654:3210:FEDC:BA98:7654:3210.

   $ IP Security Option
      (I) See: Internet Protocol Security Option.

   $ IP Security Protocol (IPsec)
      1a. (I) The name of the IETF working group that is specifying an
      architecture [R2401, R4301] and set of protocols to provide
      security services for IP traffic. (See: AH, ESP, IKE, SAD, SPD.
      Compare: IPSO.)

      1b. (I) A collective name for the IP security architecture [R4301]
      and associated set of protocols (primarily AH, ESP, and IKE).

      Usage: In IDOCs that use the abbreviation "IPsec", the letters
      "IP" SHOULD be in uppercase, and the letters "sec" SHOULD NOT.

      Tutorial: The security services provided by IPsec include access
      control service, connectionless data integrity service, data
      origin authentication service, protection against replays
      (detection of the arrival of duplicate datagrams, within a
      constrained window), data confidentiality service, and limited
      traffic-flow confidentiality. IPsec specifies (a) security
      protocols (AH and ESP), (b) security associations (what they are,
      how they work, how they are managed, and associated processing),

      (c) key management (IKE), and (d) algorithms for authentication
      and encryption. Implementation of IPsec is optional for IP version
      4, but mandatory for IP version 6. (See: transport mode, tunnel
      mode.)

   $ IPLI
      (I) See: Internet Private Line Interface.

   $ IPRA
      (I) See: Internet Policy Registration Authority.

   $ IPS
      (I) See: Internet Protocol Suite.

   $ IPsec
      (I) See: IP Security Protocol.

   $ IPSO
      (I) See: Internet Protocol Security Option.

   $ ISAKMP
      (I) See: Internet Security Association and Key Management
      Protocol.

   $ ISO
      (I) International Organization for Standardization, a voluntary,
      non-treaty, non-governmental organization, established in 1947,
      with voting members that are designated standards bodies of
      participating nations and non-voting observer organizations.
      (Compare: ANSI, IETF, ITU-T, W3C.)

      Tutorial: Legally, ISO is a Swiss, non-profit, private
      organization. ISO and the IEC (the International Electrotechnical
      Commission) form the specialized system for worldwide
      standardization. National bodies that are members of ISO or IEC
      participate in developing international standards through ISO and
      IEC technical committees that deal with particular fields of
      activity. Other international governmental and non-governmental
      organizations, in liaison with ISO and IEC, also take part. (ANSI
      is the U.S. voting member of ISO. ISO is a class D member of ITU-
      T.)

      The ISO standards development process has four levels of
      increasing maturity: Working Draft (WD), Committee Draft (CD),
      Draft International Standard (DIS), and International Standard
      (IS). (Compare: "Internet Standards Track" under "Internet
      Standard".) In information technology, ISO and IEC have a joint
      technical committee, ISO/IEC JTC 1. DISs adopted by JTC 1 are

      circulated to national bodies for voting, and publication as an IS
      requires approval by at least 75% of the national bodies casting a
      vote.

   $ ISO 17799
      (N) An International Standard that is a code of practice, derived
      from Part 1 of British Standard 7799, for managing the security of
      information systems in an organization. This standard does not
      provide definitive or specific material on any security topic. It
      provides general guidance on a wide variety of topics, but
      typically does not go into depth. (See: IATF, [SP14].)

   $ ISOC
      (I) See: Internet Society.

   $ issue
      (I) /PKI/ Generate and sign a digital certificate (or a CRL) and,
      usually, distribute it and make it available to potential
      certificate users (or CRL users). (See: certificate creation.)

      Usage: The term "issuing" is usually understood to refer not only
      to creating a digital certificate (or a CRL) but also to making it
      available to potential users, such as by storing it in a
      repository or other directory or otherwise publishing it. However,
      the ABA [DSG] explicitly limits this term to the creation process
      and excludes any related publishing or distribution process.

   $ issuer
      1. (I) /certificate, CRL/ The CA that signs a digital certificate
      or CRL.

      Tutorial: An X.509 certificate always includes the issuer's name.
      The name may include a common name value.

      2. (O) /payment card, SET/ "The financial institution or its agent
      that issues the unique primary account number to the cardholder
      for the payment card brand." [SET2]

      Tutorial: The institution that establishes the account for a
      cardholder and issues the payment card also guarantees payment for
      authorized transactions that use the card in accordance with card
      brand regulations and local legislation. [SET1]

   $ ITAR
      (O) See: International Traffic in Arms Regulations.

   $ ITSEC
      (N) See: Information Technology System Evaluation Criteria.

   $ ITU-T
      (N) International Telecommunications Union, Telecommunication
      Standardization Sector (formerly "CCITT"), a United Nations treaty
      organization that is composed mainly of postal, telephone, and
      telegraph authorities of the member countries and that publishes
      standards called "Recommendations". (See: X.400, X.500.)

      Tutorial: The Department of State represents the United States.
      ITU-T works on many kinds of communication systems. ITU-T
      cooperates with ISO on communication protocol standards, and many
      Recommendations in that area are also published as an ISO standard
      with an ISO name and number.

   $ IV
      (I) See: initialization value.

   $ jamming
      (N) An attack that attempts to interfere with the reception of
      broadcast communications. (See: anti-jam, denial of service.
      Compare: flooding.)

      Tutorial: Jamming uses "interference" as a type of "obstruction"
      intended to cause "disruption". Jamming a broadcast signal is
      typically done by broadcasting a second signal that receivers
      cannot separate from the first one. Jamming is mainly thought of
      in the context of wireless communication, but also can be done in
      some wired technologies, such as LANs that use contention
      techniques to share a broadcast medium.

   $ KAK
      (D) See: key-auto-key. (Compare: KEK.)

   $ KDC
      (I) See: Key Distribution Center.

   $ KEA
      (N) See: Key Exchange Algorithm.

   $ KEK
      (I) See: key-encrypting key. (Compare: KAK.)

   $ Kerberos
      (I) A system developed at the Massachusetts Institute of
      Technology that depends on passwords and symmetric cryptography
      (DES) to implement ticket-based, peer entity authentication
      service and access control service distributed in a client-server
      network environment. [R4120, Stei] (See: realm.)

      Tutorial: Kerberos was originally developed by Project Athena and
      is named for the mythical three-headed dog that guards Hades. The
      system architecture includes authentication servers and ticket-
      granting servers that function as an ACC and a KDC.

      RFC 4556 describes extensions to the Kerberos specification that
      modify the initial authentication exchange between a client and
      the KDC. The extensions employ public-key cryptography to enable
      the client and KDC to mutually authenticate and establish shared,
      symmetric keys that are used to complete the exchange. (See:
      PKINIT.)

   $ kernel
      (I) A small, trusted part of a system that provides services on
      which the other parts of the system depend. (See: security
      kernel.)

   $ Kernelized Secure Operating System (KSOS)
      (O) An MLS computer operating system, designed to be a provably
      secure replacement for UNIX Version 6, and consisting of a
      security kernel, non-kernel security-related utility programs, and
      optional UNIX application development and support environments.
      [Perr]

      Tutorial: KSOS-6 was the implementation on a SCOMP. KSOS-11 was
      the implementation by Ford Aerospace and Communications
      Corporation on the DEC PDP-11/45 and PDP-11/70 computers.

   $ key
      1a. (I) /cryptography/ An input parameter used to vary a
      transformation function performed by a cryptographic algorithm.
      (See: private key, public key, storage key, symmetric key, traffic
      key. Compare: initialization value.)

      1b. (O) /cryptography/ Used in singular form as a collective noun
      referring to keys or keying material. Example: A fill device can
      be used transfer key between two cryptographic devices.

      2. (I) /anti-jam/ An input parameter used to vary a process that
      determines patterns for an anti-jam measure. (See: frequency
      hopping, spread spectrum.)

      Tutorial: A key is usually specified as a sequence of bits or
      other symbols. If a key value needs to be kept secret, the
      sequence of symbols that comprise it should be random, or at least
      pseudorandom, because that makes the key harder for an adversary
      to guess. (See: brute-force attack, cryptanalysis, strength.)

   $ key agreement (algorithm or protocol)
      1. (I) A key establishment method (especially one involving
      asymmetric cryptography) by which two or more entities, without
      prior arrangement except a public exchange of data (such as public
      keys), each can generate the same key value. That is, the method
      does not send a secret from one entity to the other; instead, both
      entities, without prior arrangement except a public exchange of
      data, can compute the same secret value, but that value cannot be
      computed by other, unauthorized entities. (See: Diffie-Hellman-
      Merkle, key establishment, KEA, MQV. Compare: key transport.)

      2. (O) "A method for negotiating a key value on line without
      transferring the key, even in an encrypted form, e.g., the Diffie-
      Hellman technique." [X509] (See: Diffie-Hellman-Merkle.)

      3. (O) "The procedure whereby two different parties generate
      shared symmetric keys such that any of the shared symmetric keys
      is a function of the information contributed by all legitimate
      participants, so that no party [alone] can predetermine the value
      of the key." [A9042]

      Example: A message originator and the intended recipient can each
      use their own private key and the other's public key with the
      Diffie-Hellman-Merkle algorithm to first compute a shared secret
      value and, from that value, derive a session key to encrypt the
      message.

   $ key authentication
      (N) "The assurance of the legitimate participants in a key
      agreement [i.e., in a key-agreement protocol] that no non-
      legitimate party possesses the shared symmetric key." [A9042]

   $ key-auto-key (KAK)
      (D) "Cryptographic logic [i.e., a mode of operation] using
      previous key to produce key." [C4009, A1523] (See: CTAK,
      /cryptographic operation/ under "mode".)

      Deprecated Term: IDOCs SHOULD NOT use this term; it is neither
      well-known nor precisely defined. Instead, use terms associated
      with modes that are defined in standards, such as CBC, CFB, and
      OFB.

   $ key center
      (I) A centralized, key-distribution process (used in symmetric
      cryptography), usually a separate computer system, that uses
      master keys (i.e., KEKs) to encrypt and distribute session keys
      needed by a community of users.

      Tutorial: An ANSI standard [A9017] defines two types of key
      center: "key distribution center" and "key translation center".

   $ key confirmation
      (N) "The assurance [provided to] the legitimate participants in a
      key establishment protocol that the [parties that are intended to
      share] the symmetric key actually possess the shared symmetric
      key." [A9042]

   $ key distribution
      (I) A process that delivers a cryptographic key from the location
      where it is generated to the locations where it is used in a
      cryptographic algorithm. (See: key establishment, key management.)

   $ key distribution center (KDC)
      1. (I) A type of key center (used in symmetric cryptography) that
      implements a key-distribution protocol to provide keys (usually,
      session keys) to two (or more) entities that wish to communicate
      securely. (Compare: key translation center.)

      2. (N) "COMSEC facility generating and distributing key in
      electrical form." [C4009]

      Tutorial: A KDC distributes keys to Alice and Bob, who (a) wish to
      communicate with each other but do not currently share keys, (b)
      each share a KEK with the KDC, and (c) may not be able to generate
      or acquire keys by themselves. Alice requests the keys from the
      KDC. The KDC generates or acquires the keys and makes two
      identical sets. The KDC encrypts one set in the KEK it shares with
      Alice, and sends that encrypted set to Alice. The KDC encrypts the
      second set in the KEK it shares with Bob, and either (a) sends
      that encrypted set to Alice for her to forward to Bob or (b) sends
      it directly to Bob (although the latter option is not supported in
      the ANSI standard [A9017]).

   $ key encapsulation
      (N) A key recovery technique for storing knowledge of a
      cryptographic key by encrypting it with another key and ensuring
      that only certain third parties called "recovery agents" can
      perform the decryption operation to retrieve the stored key. Key
      encapsulation typically permits direct retrieval of a secret key
      used to provide data confidentiality. (Compare: key escrow.)

   $ key-encrypting key (KEK)
      (I) A cryptographic key that (a) is used to encrypt other keys
      (either DEKs or other TEKs) for transmission or storage but (b)
      (usually) is not used to encrypt application data. Usage:
      Sometimes called "key-encryption key".

   $ key escrow
      (N) A key recovery technique for storing knowledge of a
      cryptographic key or parts thereof in the custody of one or more
      third parties called "escrow agents", so that the key can be
      recovered and used in specified circumstances. (Compare: key
      encapsulation.)

      Tutorial: Key escrow is typically implemented with split knowledge
      techniques. For example, the Escrowed Encryption Standard [FP185]
      entrusts two components of a device-unique split key to separate
      escrow agents. The agents provide the components only to someone
      legally authorized to conduct electronic surveillance of
      telecommunications encrypted by that specific device. The
      components are used to reconstruct the device-unique key, and it
      is used to obtain the session key needed to decrypt
      communications.

   $ key establishment (algorithm or protocol)
      1. (I) A procedure that combines the key-generation and key-
      distribution steps needed to set up or install a secure
      communication association.

      2. (I) A procedure that results in keying material being shared
      among two or more system entities. [A9042, SP56]

      Tutorial: The two basic techniques for key establishment are "key
      agreement" and "key transport".

   $ Key Exchange Algorithm (KEA)
      (N) A key-agreement method [SKIP, R2773] that is based on the
      Diffie-Hellman-Merkle algorithm and uses 1024-bit asymmetric keys.
      (See: CAPSTONE, CLIPPER, FORTEZZA, SKIPJACK.)

      Tutorial: KEA was developed by NSA and formerly classified at the
      U.S. DoD "Secret" level. On 23 June 1998, the NSA announced that
      KEA had been declassified.

   $ key generation
      (I) A process that creates the sequence of symbols that comprise a
      cryptographic key. (See: key management.)

   $ key generator
      1. (I) An algorithm that uses mathematical rules to
      deterministically produce a pseudorandom sequence of cryptographic
      key values.

      2. (I) An encryption device that incorporates a key-generation
      mechanism and applies the key to plain text to produce cipher text

      (e.g., by exclusive OR-ing (a) a bit-string representation of the
      key with (b) a bit-string representation of the plaintext).

   $ key length
      (I) The number of symbols (usually stated as a number of bits)
      needed to be able to represent any of the possible values of a
      cryptographic key. (See: key space.)

   $ key lifetime
      1. (D) Synonym for "cryptoperiod".

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 1 because a key's cryptoperiod may be only a part of
      the key's lifetime. A key could be generated at some time prior to
      when its cryptoperiod begins and might not be destroyed (i.e.,
      zeroized) until some time after its cryptoperiod ends.

      2. (O) /MISSI/ An attribute of a MISSI key pair that specifies a
      time span that bounds the validity period of any MISSI X.509
      public-key certificate that contains the public component of the
      pair. (See: cryptoperiod.)

   $ key loader
      (N) Synonym for "fill device".

   $ key loading and initialization facility (KLIF)
      (N) A place where ECU hardware is activated after being
      fabricated. (Compare: CLEF.)

      Tutorial: Before going to its KLIF, an ECU is not ready to be
      fielded, usually because it is not yet able to receive DEKs. The
      KLIF employs trusted processes to complete the ECU by installing
      needed data such as KEKs, seed values, and, in some cases,
      cryptographic software. After KLIF processing, the ECU is ready
      for deployment.

   $ key management
      1a. (I) The process of handling keying material during its life
      cycle in a cryptographic system; and the supervision and control
      of that process. (See: key distribution, key escrow, keying
      material, public-key infrastructure.)

      Usage: Usually understood to include ordering, generating,
      storing, archiving, escrowing, distributing, loading, destroying,
      auditing, and accounting for the material.

      1b. (O) /NIST/ "The activities involving the handling of
      cryptographic keys and other related security parameters (e.g.,

      IVs, counters) during the entire life cycle of the keys, including
      their generation, storage, distribution, entry and use, deletion
      or destruction, and archiving." [FP140, SP57]

      2. (O) /OSIRM/ "The generation, storage, distribution, deletion,
      archiving and application of keys in accordance with a security
      policy." [I7498-2]

   $ Key Management Protocol (KMP)
      (N) A protocol to establish a shared symmetric key between a pair
      (or a group) of users. (One version of KMP was developed by SDNS,
      and another by SILS.) Superseded by ISAKMP and IKE.

   $ key material
      (D) Synonym for "keying material".

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      "keying material".

   $ key pair
      (I) A set of mathematically related keys -- a public key and a
      private key -- that are used for asymmetric cryptography and are
      generated in a way that makes it computationally infeasible to
      derive the private key from knowledge of the public key. (See:
      Diffie-Hellman-Merkle, RSA.)

      Tutorial: A key pair's owner discloses the public key to other
      system entities so they can use the key to (a) encrypt data, (b)
      verify a digital signature, or (c) generate a key with a key-
      agreement algorithm. The matching private key is kept secret by
      the owner, who uses it to (a') decrypt data, (b') generate a
      digital signature, or (c') generate a key with a key-agreement
      algorithm.

   $ key recovery
      1. (I) /cryptanalysis/ A process for learning the value of a
      cryptographic key that was previously used to perform some
      cryptographic operation. (See: cryptanalysis, recovery.)

      2. (I) /backup/ Techniques that provide an intentional, alternate
      means to access the key used for data confidentiality service in
      an encrypted association. [DoD4] (Compare: recovery.)

      Tutorial: It is assumed that the cryptographic system includes a
      primary means of obtaining the key through a key-establishment
      algorithm or protocol. For the secondary means, there are two
      classes of key recovery techniques: key encapsulation and key
      escrow.

   $ key space
      (I) The range of possible values of a cryptographic key; or the
      number of distinct transformations supported by a particular
      cryptographic algorithm. (See: key length.)

   $ key translation center
      (I) A type of key center that implements a key-distribution
      protocol (based on symmetric cryptography) to convey keys between
      two (or more) parties who wish to communicate securely. (Compare:
      key distribution center.)

      Tutorial: A key translation center transfers keys for future
      communication between Bob and Alice, who (a) wish to communicate
      with each other but do not currently share keys, (b) each share a
      KEK with the center, and (c) have the ability to generate or
      acquire keys by themselves. Alice generates or acquires a set of
      keys for communication with Bob. Alice encrypts the set in the KEK
      she shares with the center and sends the encrypted set to the
      center. The center decrypts the set, reencrypts the set in the KEK
      it shares with Bob, and either (a) sends that reencrypted set to
      Alice for her to forward to Bob or (b) sends it directly to Bob
      (although direct distribution is not supported in the ANSI
      standard [A9017]).

   $ key transport (algorithm or protocol)
      1. (I) A key establishment method by which a secret key is
      generated by a system entity in a communication association and
      securely sent to another entity in the association. (Compare: key
      agreement.)

      Tutorial: Either (a) one entity generates a secret key and
      securely sends it to the other entity, or (b) each entity
      generates a secret value and securely sends it to the other
      entity, where the two values are combined to form a secret key.
      For example, a message originator can generate a random session
      key and then use the RSA algorithm to encrypt that key with the
      public key of the intended recipient.

      2. (O) "The procedure to send a symmetric key from one party to
      other parties. As a result, all legitimate participants share a
      common symmetric key in such a way that the symmetric key is
      determined entirely by one party." [A9042]

   $ key update
      1. (I) Derive a new key from an existing key. (Compare: rekey.)

      2. (O) Irreversible cryptographic process that modifies a key to
      produce a new key. [C4009]

   $ key validation
      1. (I) "The procedure for the receiver of a public key to check
      that the key conforms to the arithmetic requirements for such a
      key in order to thwart certain types of attacks." [A9042] (See:
      weak key)

      2. (D) Synonym for "certificate validation".

      Deprecated Usage: IDOCs SHOULD NOT use the term as a synonym for
      "certificate validation"; that would unnecessarily duplicate the
      meaning of the latter term and mix concepts in a potentially
      misleading way. In validating an X.509 public-key certificate, the
      public key contained in the certificate is normally treated as an
      opaque data object.

   $ keyed hash
      (I) A cryptographic hash (e.g., [R1828]) in which the mapping to a
      hash result is varied by a second input parameter that is a
      cryptographic key. (See: checksum.)

      Tutorial: If the input data object is changed, a new,
      corresponding hash result cannot be correctly computed without
      knowledge of the secret key. Thus, the secret key protects the
      hash result so it can be used as a checksum even when there is a
      threat of an active attack on the data. There are two basic types
      of keyed hash:
      -  A function based on a keyed encryption algorithm. Example: Data
         Authentication Code.
      -  A function based on a keyless hash that is enhanced by
         combining (e.g., by concatenating) the input data object
         parameter with a key parameter before mapping to the hash
         result. Example: HMAC.

   $ keying material
      1. (I) Data that is needed to establish and maintain a
      cryptographic security association, such as keys, key pairs, and
      IVs.

      2. (O) "Key, code, or authentication information in physical or
      magnetic form." [C4009] (Compare: COMSEC material.)

   $ keying material identifier (KMID)
      1. (I) An identifier assigned to an item of keying material.

      2. (O) /MISSI/ A 64-bit identifier that is assigned to a key pair
      when the public key is bound in a MISSI X.509 public-key
      certificate.

   $ Khafre
      (N) A patented, symmetric block cipher designed by Ralph C. Merkle
      as a plug-in replacement for DES. [Schn]

      Tutorial: Khafre was designed for efficient encryption of small
      amounts of data. However, because Khafre does not precompute
      tables used for encryption, it is slower than Khufu for large
      amounts of data.

   $ Khufu
      (N) A patented, symmetric block cipher designed by Ralph C. Merkle
      as a plug-in replacement for DES. [Schn]

      Tutorial: Khufu was designed for fast encryption of large amounts
      of data. However, because Khufu precomputes tables used in
      encryption, it is less efficient than Khafre for small amounts of
      data.

   $ KLIF
      (N) See: key loading and initialization facility.

   $ KMID
      (I) See: keying material identifier.

   $ known-plaintext attack
      (I) A cryptanalysis technique in which the analyst tries to
      determine the key from knowledge of some plaintext-ciphertext
      pairs (although the analyst may also have other clues, such as
      knowing the cryptographic algorithm).

   $ kracker
      (O) Old spelling for "cracker".

   $ KSOS, KSOS-6, KSOS-11
      (O) See: Kernelized Secure Operating System.

   $ L2F
      (N) See: Layer 2 Forwarding Protocol.

   $ L2TP
      (N) See: Layer 2 Tunneling Protocol.

   $ label
      See: time stamp, security label.

   $ laboratory attack
      (O) "Use of sophisticated signal recovery equipment in a
      laboratory environment to recover information from data storage
      media." [C4009]

   $ LAN
      (I) Abbreviation for "local area network" [R1983]. (See: [FP191].)

   $ land attack
      (I) A denial-of-service attack that sends an IP packet that (a)
      has the same address in both the Source Address and Destination
      Address fields and (b) contains a TCP SYN packet that has the same
      port number in both the Source Port and Destination Port fields.

      Derivation: This single-packet attack was named for "land", the
      program originally published by the cracker who invented this
      exploit. Perhaps that name was chosen because the inventor thought
      of multi-packet (i.e., flooding) attacks as arriving by sea.

   $ Language of Temporal Ordering Specification (LOTOS)
      (N) A language (ISO 8807-1990) for formal specification of
      computer network protocols; describes the order in which events
      occur.

   $ lattice
      (I) A finite set together with a partial ordering on its elements
      such that for every pair of elements there is a least upper bound
      and a greatest lower bound.

      Example: A lattice is formed by a finite set S of security levels
      -- i.e., a set S of all ordered pairs (x,c), where x is one of a
      finite set X of hierarchically ordered classification levels X(1),
      non-hierarchical categories C(1), ..., C(M) -- together with the
      "dominate" relation. Security level (x,c) is said to "dominate"
      (x',c') if and only if (a) x is greater (higher) than or equal to
      x' and (b) c includes at least all of the elements of c'. (See:
      dominate, lattice model.)

      Tutorial: Lattices are used in some branches of cryptography, both
      as a basis for hard computational problems upon which
      cryptographic algorithms can be defined, and also as a basis for
      attacks on cryptographic algorithms.

   $ lattice model
      1. (I) A description of the semantic structure formed by a finite
      set of security levels, such as those used in military
      organizations. (See: dominate, lattice, security model.)

      2. (I) /formal model/ A model for flow control in a system, based
      on the lattice that is formed by the finite security levels in a
      system and their partial ordering. [Denn]

   $ Law Enforcement Access Field (LEAF)
      (N) A data item that is automatically embedded in data encrypted
      by devices (e.g., CLIPPER chip) that implement the Escrowed
      Encryption Standard.

   $ Layer 1, 2, 3, 4, 5, 6, 7
      (N) See: OSIRM.

   $ Layer 2 Forwarding Protocol (L2F)
      (N) An Internet protocol (originally developed by Cisco
      Corporation) that uses tunneling of PPP over IP to create a
      virtual extension of a dial-up link across a network, initiated by
      the dial-up server and transparent to the dial-up user. (See:
      L2TP.)

   $ Layer 2 Tunneling Protocol (L2TP)
      (N) An Internet client-server protocol that combines aspects of
      PPTP and L2F and supports tunneling of PPP over an IP network or
      over frame relay or other switched network. (See: VPN.)

      Tutorial: PPP can in turn encapsulate any OSIRM Layer 3 protocol.
      Thus, L2TP does not specify security services; it depends on
      protocols layered above and below it to provide any needed
      security.

   $ LDAP
      (I) See: Lightweight Directory Access Protocol.

   $ least common mechanism
      (I) The principle that a security architecture should minimize
      reliance on mechanisms that are shared by many users.

      Tutorial: Shared mechanisms may include cross-talk paths that
      permit a breach of data security, and it is difficult to make a
      single mechanism operate in a correct and trusted manner to the
      satisfaction of a wide range of users.

   $ least privilege
      (I) The principle that a security architecture should be designed
      so that each system entity is granted the minimum system resources
      and authorizations that the entity needs to do its work. (Compare:
      economy of mechanism, least trust.)

      Tutorial: This principle tends to limit damage that can be caused
      by an accident, error, or unauthorized act. This principle also
      tends to reduce complexity and promote modularity, which can make
      certification easier and more effective. This principle is similar
      to the principle of protocol layering, wherein each layer provides
      specific, limited communication services, and the functions in one
      layer are independent of those in other layers.

   $ least trust
      (I) The principle that a security architecture should be designed
      in a way that minimizes (a) the number of components that require
      trust and (b) the extent to which each component is trusted.
      (Compare: least privilege, trust level.)

   $ legacy system
      (I) A system that is in operation but will not be improved or
      expanded while a new system is being developed to supersede it.

   $ legal non-repudiation
      (I) See: secondary definition under "non-repudiation".

   $ leap of faith
      1. (I) /general security/ Operating a system as though it began
      operation in a secure state, even though it cannot be proven that
      such a state was established (i.e., even though a security
      compromise might have occurred at or before the time when
      operation began).

      2. (I) /COMSEC/ The initial part, i.e., the first communication
      step, or steps, of a protocol that is vulnerable to attack
      (especially a man-in-the-middle attack) during that part but, if
      that part is completed without being attacked, is subsequently not
      vulnerable in later steps (i.e., results in a secure communication
      association for which no man-in-the-middle attack is possible).

      Usage: This term is listed in English dictionaries, but their
      definitions are broad and can be interpreted in many ways in
      Internet contexts. Similarly, the definition stated here can be
      interpreted in several ways. Therefore, IDOCs that use this term
      (especially IDOCs that are protocol specifications) SHOULD state a
      more specific definition for it.

      Tutorial: In a protocol, a leap of faith typically consists of
      accepting a claim of peer identity, data origin, or data integrity
      without authenticating that claim. When a protocol includes such a
      step, the protocol might also be designed so that if a man-in-
      the-middle attack succeeds during the vulnerable first part, then
      the attacker must remain in the middle for all subsequent

      exchanges or else one of the legitimate parties will be able to
      detect the attack.

   $ level of concern
      (N) /U.S. DoD/ A rating assigned to an information system that
      indicates the extent to which protective measures, techniques, and
      procedures must be applied. (See: critical, sensitive, level of
      robustness.)

   $ level of robustness
      (N) /U.S. DoD/ A characterization of (a) the strength of a
      security function, mechanism, service, or solution and (b) the
      assurance (or confidence) that it is implemented and functioning.
      [Cons, IATF] (See: level of concern.)

   $ Liberty Alliance
      (O) An international consortium of more than 150 commercial,
      nonprofit, and governmental organizations that was created in 2001
      to address technical, business, and policy problems of identity
      and identity-based Web services and develop a standard for
      federated network identity that supports current and emerging
      network devices.

   $ Lightweight Directory Access Protocol (LDAP)
      (I) An Internet client-server protocol (RFC 3377) that supports
      basic use of the X.500 Directory (or other directory servers)
      without incurring the resource requirements of the full Directory
      Access Protocol (DAP).

      Tutorial: Designed for simple management and browser applications
      that provide simple read/write interactive directory service.
      Supports both simple authentication and strong authentication of
      the client to the directory server.

   $ link
      1a. (I) A communication facility or physical medium that can
      sustain data communications between multiple network nodes, in the
      protocol layer immediately below IP. (RFC 3753)

      1b. (I) /subnetwork/ A communication channel connecting subnetwork
      relays (especially one between two packet switches) that is
      implemented at OSIRM Layer 2. (See: link encryption.)

      Tutorial: The relay computers assume that links are logically
      passive. If a computer at one end of a link sends a sequence of
      bits, the sequence simply arrives at the other end after a finite
      time, although some bits may have been changed either accidentally
      (errors) or by active wiretapping.

      2. (I) /World Wide Web/ See: hyperlink.

   $ link encryption
      (I) Stepwise (link-by-link) protection of data that flows between
      two points in a network, provided by encrypting data separately on
      each network link, i.e., by encrypting data when it leaves a host
      or subnetwork relay and decrypting when it arrives at the next
      host or relay. Each link may use a different key or even a
      different algorithm. [R1455] (Compare: end-to-end encryption.)

   $ liveness
      (I) A property of a communication association or a feature of a
      communication protocol that provides assurance to the recipient of
      data that the data is being freshly transmitted by its originator,
      i.e., that the data is not being replayed, by either the
      originator or a third party, from a previous transmission. (See:
      fresh, nonce, replay attack.)

   $ logic bomb
      (I) Malicious logic that activates when specified conditions are
      met. Usually intended to cause denial of service or otherwise
      damage system resources. (See: Trojan horse, virus, worm.)

   $ login
      1a. (I) An act by which a system entity establishes a session in
      which the entity can use system resources. (See: principal,
      session.)

      1b. (I) An act by which a system user has its identity
      authenticated by the system. (See: principal, session.)

      Usage: Usually understood to be accomplished by providing an
      identifier and matching authentication information (e.g., a
      password) to a security mechanism that authenticates the user's
      identity; but sometimes refers to establishing a connection with a
      server when no authentication or specific authorization is
      involved.

      Derivation: Refers to "log" file, a security audit trail that
      records (a) security events, such as the beginning of a session,
      and (b) the names of the system entities that initiate events.

   $ long title
      (O) /U.S. Government/ "Descriptive title of [an item of COMSEC
      material]." [C4009] (Compare: short title.)

   $ low probability of detection
      (I) Result of TRANSEC measures used to hide or disguise a
      communication.

   $ low probability of intercept
      (I) Result of TRANSEC measures used to prevent interception of a
      communication.

   $ LOTOS
      (N) See: Language of Temporal Ordering Specification.

   $ MAC
      (N) See: mandatory access control, Message Authentication Code.

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because this abbreviation is ambiguous.

   $ magnetic remanence
      (N) Magnetic representation of residual information remaining on a
      magnetic medium after the medium has been cleared. [NCS25] (See:
      clear, degauss, purge.)

   $ main mode
      (I) See: /IKE/ under "mode".

   $ maintenance hook
      (N) "Special instructions (trapdoors) in software allowing easy
      maintenance and additional feature development. Since maintenance
      hooks frequently allow entry into the code without the usual
      checks, they are a serious security risk if they are not removed
      prior to live implementation." [C4009] (See: back door.)

   $ malicious logic
      (I) Hardware, firmware, or software that is intentionally included
      or inserted in a system for a harmful purpose. (See: logic bomb,
      Trojan horse, spyware, virus, worm. Compare: secondary definitions
      under "corruption", "incapacitation", "masquerade", and "misuse".)

   $ malware
      (D) A contraction of "malicious software". (See: malicious logic.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it is not listed
      in most dictionaries and could confuse international readers.

   $ MAN
      (I) metropolitan area network.

   $ man-in-the-middle attack
      (I) A form of active wiretapping attack in which the attacker
      intercepts and selectively modifies communicated data to
      masquerade as one or more of the entities involved in a
      communication association. (See: hijack attack, piggyback attack.)

      Tutorial: For example, suppose Alice and Bob try to establish a
      session key by using the Diffie-Hellman-Merkle algorithm without
      data origin authentication service. A "man in the middle" could
      (a) block direct communication between Alice and Bob and then (b)
      masquerade as Alice sending data to Bob, (c) masquerade as Bob
      sending data to Alice, (d) establish separate session keys with
      each of them, and (e) function as a clandestine proxy server
      between them to capture or modify sensitive information that Alice
      and Bob think they are sending only to each other.

   $ manager
      (I) A person who controls the service configuration of a system or
      the functional privileges of operators and other users. (See:
      administrative security. Compare: operator, SSO, user.)

   $ mandatory access control
      1. (I) An access control service that enforces a security policy
      based on comparing (a) security labels, which indicate how
      sensitive or critical system resources are, with (b) security
      clearances, which indicate that system entities are eligible to
      access certain resources. (See: discretionary access control, MAC,
      rule-based security policy.)

      Derivation: This kind of access control is called "mandatory"
      because an entity that has clearance to access a resource is not
      permitted, just by its own volition, to enable another entity to
      access that resource.

      2. (O) "A means of restricting access to objects based on the
      sensitivity (as represented by a label) of the information
      contained in the objects and the formal authorization (i.e.,
      clearance) of subjects to access information of such sensitivity."
      [DoD1]

   $ manipulation detection code
      (D) Synonym for "checksum".

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "checksum"; the word "manipulation" implies protection against
      active attacks, which an ordinary checksum might not provide.
      Instead, if such protection is intended, use "protected checksum"
      or some particular type thereof, depending on which is meant. If

      such protection is not intended, use "error detection code" or
      some specific type of checksum that is not protected.

   $ marking
      See: time stamp, security marking.

   $ MARS
      (O) A symmetric, 128-bit block cipher with variable key length
      (128 to 448 bits), developed by IBM as a candidate for the AES.

   $ Martian
      (D) /slang/ A packet that arrives unexpectedly at the wrong
      address or on the wrong network because of incorrect routing or
      because it has a non-registered or ill-formed IP address. [R1208]

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ masquerade
      (I) A type of threat action whereby an unauthorized entity gains
      access to a system or performs a malicious act by illegitimately
      posing as an authorized entity. (See: deception.)

      Usage: This type of threat action includes the following subtypes:
      -  "Spoof": Attempt by an unauthorized entity to gain access to a
         system by posing as an authorized user.
      -  "Malicious logic": In context of masquerade, any hardware,
         firmware, or software (e.g., Trojan horse) that appears to
         perform a useful or desirable function, but actually gains
         unauthorized access to system resources or tricks a user into
         executing other malicious logic. (See: corruption,
         incapacitation, main entry for "malicious logic", misuse.)

   $ MCA
      (O) See: merchant certification authority.

   $ MD2
      (N) A cryptographic hash [R1319] that produces a 128-bit hash
      result, was designed by Ron Rivest, and is similar to MD4 and MD5
      but slower.

      Derivation: Apparently, an abbreviation of "message digest", but
      that term is deprecated by this Glossary.

   $ MD4
      (N) A cryptographic hash [R1320] that produces a 128-bit hash
      result and was designed by Ron Rivest. (See: Derivation under
      "MD2", SHA-1.)

   $ MD5
      (N) A cryptographic hash [R1321] that produces a 128-bit hash
      result and was designed by Ron Rivest to be an improved version of
      MD4. (See: Derivation under "MD2".)

   $ merchant
      (O) /SET/ "A seller of goods, services, and/or other information
      who accepts payment for these items electronically." [SET2] A
      merchant may also provide electronic selling services and/or
      electronic delivery of items for sale. With SET, the merchant can
      offer its cardholders secure electronic interactions, but a
      merchant that accepts payment cards is required to have a
      relationship with an acquirer. [SET1, SET2]

   $ merchant certificate
      (O) /SET/ A public-key certificate issued to a merchant. Sometimes
      used to refer to a pair of such certificates where one is for
      digital signature use and the other is for encryption.

   $ merchant certification authority (MCA)
      (O) /SET/ A CA that issues digital certificates to merchants and
      is operated on behalf of a payment card brand, an acquirer, or
      another party according to brand rules. Acquirers verify and
      approve requests for merchant certificates prior to issuance by
      the MCA. An MCA does not issue a CRL, but does distribute CRLs
      issued by root CAs, brand CAs, geopolitical CAs, and payment
      gateway CAs. [SET2]

   $ mesh PKI
      (I) A non-hierarchical PKI architecture in which there are several
      trusted CAs rather than a single root. Each certificate user bases
      path validations on the public key of one of the trusted CAs,
      usually the one that issued that user's own public-key
      certificate. Rather than having superior-to-subordinate
      relationships between CAs, the relationships are peer-to-peer, and
      CAs issue cross-certificates to each other. (Compare: hierarchical
      PKI, trust-file PKI.)

   $ Message Authentication Code (MAC), message authentication code
      1. (N) /capitalized/ A specific ANSI standard for a checksum that
      is computed with a keyed hash that is based on DES. [A9009] Usage:
      a.k.a. Data Authentication Code, which is a U.S. Government
      standard. [FP113] (See: MAC.)

      2. (D) /not capitalized/ Synonym for "error detection code".

      Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form
      "message authentication code". Instead, use "checksum", "error
      detection code", "hash", "keyed hash", "Message Authentication
      Code", or "protected checksum", depending on what is meant. (See:
      authentication code.)

      The uncapitalized form mixes concepts in a potentially misleading
      way. The word "message" is misleading because it implies that the
      mechanism is particularly suitable for or limited to electronic
      mail (see: Message Handling Systems). The word "authentication" is
      misleading because the mechanism primarily serves a data integrity
      function rather than an authentication function. The word "code"
      is misleading because it implies that either encoding or
      encryption is involved or that the term refers to computer
      software.

   $ message digest
      (D) Synonym for "hash result". (See: cryptographic hash.)

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "hash result"; this term unnecessarily duplicates the meaning of
      the other, more general term and mixes concepts in a potentially
      misleading way. The word "message" is misleading because it
      implies that the mechanism is particularly suitable for or limited
      to electronic mail (see: Message Handling Systems).

   $ message handling system
      (D) Synonym for the Internet electronic mail system.

      Deprecated Term: IDOCs SHOULD NOT use this term, because it could
      be confused with Message Handling System. Instead, use "Internet
      electronic mail" or some other, more specific term.

   $ Message Handling System
      (O) An ITU-T system concept that encompasses the notion of
      electronic mail but defines more comprehensive OSI systems and
      services that enable users to exchange messages on a store-and-
      forward basis. (The ISO equivalent is "Message Oriented Text
      Interchange System".) (See: X.400.)

   $ message indicator
      1. (D) /cryptographic function/ Synonym for "initialization
      value". (Compare: indicator.)

      2. (D) "Sequence of bits transmitted over a communications system
      for synchronizing cryptographic equipment." [C4009]

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "initialization value"; the term mixes concepts in a potentially
      misleading way. The word "message" is misleading because it
      suggests that the mechanism is specific to electronic mail. (See:
      Message Handling System.)

   $ message integrity check
   $ message integrity code (MIC)
      (D) Synonyms for some form of "checksum".

      Deprecated Term: IDOCs SHOULD NOT use these terms for any form of
      checksum. Instead, use "checksum", "error detection code", "hash",
      "keyed hash", "Message Authentication Code", or "protected
      checksum", depending on what is meant.

      These two terms mix concepts in potentially misleading ways. The
      word "message" is misleading because it suggests that the
      mechanism is particularly suitable for or limited to electronic
      mail. The word "integrity" is misleading because the checksum may
      be used to perform a data origin authentication function rather
      than an integrity function. The word "code" is misleading because
      it suggests either that encoding or encryption is involved or that
      the term refers to computer software.

   $ Message Security Protocol (MSP)
      (N) A secure message handling protocol [SDNS7] for use with X.400
      and Internet mail protocols. Developed by NSA's SDNS program and
      used in the U.S. DoD's Defense Message System.

   $ meta-data
      (I) Descriptive information about a data object; i.e., data about
      data, or data labels that describe other data. (See: security
      label. Compare: metadata)

      Tutorial: Meta-data can serve various management purposes:
      -  System management: File name, type, size, creation date.
      -  Application management: Document title, version, author.
      -  Usage management: Data categories, keywords, classifications.

      Meta-data can be associated with a data object in two basic ways:
      -  Explicitly: Be part of the data object (e.g., a header field of
         a data file or packet) or be linked to the object.
      -  Implicitly: Be associated with the data object because of some
         other, explicit attribute of the object.

   $ metadata, Metadata(trademark), METADATA(trademark)
      (D) Proprietary variants of "meta-data". (See: SPAM(trademark).)

      Deprecated Usage: IDOCs SHOULD NOT use these unhypenated forms;
      IDOCs SHOULD use only the uncapitalized, hyphenated "meta-data".
      The terms "Metadata" and "METADATA" are claimed as registered
      trademarks (numbers 1,409,260 and 2,185,504) owned by The Metadata
      Company, originally known as Metadata Information Partners, a
      company founded by Jack Myers. The status of "metadata" is
      unclear.

   $ MHS
      (N) See: message handling system.

   $ MIC
      (D) See: message integrity code.

   $ MIME
      (I) See: Multipurpose Internet Mail Extensions.

   $ MIME Object Security Services (MOSS)
      (I) An Internet protocol [R1848] that applies end-to-end
      encryption and digital signature to MIME message content, using
      symmetric cryptography for encryption and asymmetric cryptography
      for key distribution and signature. MOSS is based on features and
      specifications of PEM. (See: S/MIME.)

   $ Minimum Interoperability Specification for PKI Components (MISPC)
      (N) A technical description to provide a basis for interoperation
      between PKI components from different vendors; consists primarily
      of a profile of certificate and CRL extensions and a set of
      transactions for PKI operation. [SP15]

   $ misappropriation
      (I) A type of threat action whereby an entity assumes unauthorized
      logical or physical control of a system resource. (See:
      usurpation.)

      Usage: This type of threat action includes the following subtypes:
      -  Theft of data: Unauthorized acquisition and use of data
         contained in a system.
      -  Theft of service: Unauthorized use of a system service.
      -  Theft of functionality: Unauthorized acquisition of actual
         hardware, firmware, or software of a system component.

   $ MISPC
      (N) See: Minimum Interoperability Specification for PKI
      Components.

   $ MISSI
      (O) Multilevel Information System Security Initiative, an NSA
      program to encourage development of interoperable, modular
      products for constructing secure network information systems in
      support of a wide variety of U.S. Government missions. (See: MSP,
      SP3, SP4.)

   $ MISSI user
      (O) /MISSI/ A system entity that is the subject of one or more
      MISSI X.509 public-key certificates issued under a MISSI
      certification hierarchy. (See: personality.)

      Tutorial: MISSI users include both end users and the authorities
      that issue certificates. A MISSI user is usually a person but may
      be a machine or other automated process. Machines that are
      required to operate nonstop may be issued their own certificates
      to avoid downtime needed to exchange the FORTEZZA cards of machine
      operators at shift changes.

   $ mission
      (I) A statement of a (relatively long-term) duty or (relatively
      short-term) task that is assigned to an organization or system,
      indicates the purpose and objectives of the duty or task, and may
      indicate the actions to be taken to achieve it.

   $ mission critical
      (I) A condition of a system service or other system resource such
      that denial of access to, or lack of availability of, the resource
      would jeopardize a system user's ability to perform a primary
      mission function or would result in other serious consequences.
      (See: Critical. Compare: mission essential.)

   $ mission essential
      (O) /U.S. DoD/ Refers to materiel that is authorized and available
      to combat, combat support, combat service support, and combat
      readiness training forces to accomplish their assigned missions.
      [JP1] (Compare: mission critical.)

   $ misuse
      1. (I) The intentional use (by authorized users) of system
      resources for other than authorized purposes. Example: An
      authorized system administrator creates an unauthorized account
      for a friend. (See: misuse detection.)

      2. (I) A type of threat action that causes a system component to
      perform a function or service that is detrimental to system
      security. (See: usurpation.)

      Usage: This type of threat action includes the following subtypes:
      -  "Tampering": /misuse/ Deliberately altering a system's logic,
         data, or control information to cause the system to perform
         unauthorized functions or services. (See: corruption, main
         entry for "tampering".)
      -  "Malicious logic": /misuse/ Any hardware, firmware, or software
         intentionally introduced into a system to perform or control
         execution of an unauthorized function or service. (See:
         corruption, incapacitation, main entry for "malicious logic",
         masquerade.)
      -  "Violation of authorizations": Action by an entity that exceeds
         the entity's system privileges by executing an unauthorized
         function. (See: authorization.)

   $ misuse detection
      (I) An intrusion detection method that is based on rules that
      specify system events, sequences of events, or observable
      properties of a system that are believed to be symptomatic of
      security incidents. (See: IDS, misuse. Compare: anomaly
      detection.)

   $ MLS
      (I) See: multilevel secure

   $ mobile code
      1a. (I) Software that originates from a remote server, is
      transmitted across a network, and is loaded onto and executed on a
      local client system without explicit initiation by the client's
      user and, in some cases, without that user's knowledge. (Compare:
      active content.)

      Tutorial: One form of mobile code is active content in a file that
      is transferred across a network.

      1b. (O) /U.S. DoD/ "Software modules obtained from remote systems,
      transferred across a network, and then downloaded and executed on
      local systems without explicit installation or execution by the
      recipient." [JP1]

      2a. (O) /U.S. DoD/ Technology that enables the creation of
      executable information that can be delivered to an information
      system and directly executed on any hardware/software architecture
      that has an appropriate host execution environment.

      2b. (O) "Programs (e.g., script, macro, or other portable
      instruction) that can be shipped unchanged to a heterogeneous
      collection of platforms and executed with identical semantics"
      [SP28]. (See: active content.)

      Tutorial: Mobile code might be malicious. Using techniques such as
      "code signing" and a "sandbox" can reduce the risks of receiving
      and executing mobile code.

   $ mode
   $ mode of operation
      1. (I) /cryptographic operation/ A technique for enhancing the
      effect of a cryptographic algorithm or adapting the algorithm for
      an application, such as applying a block cipher to a sequence of
      data blocks or a data stream. (See: CBC, CCM, CMAC, CFB, CTR, ECB,
      OFB.)

      2. (I) /system operation/ A type of security policy that states
      the range of classification levels of information that a system is
      permitted to handle and the range of clearances and authorizations
      of users who are permitted to access the system. (See:
      compartmented security mode, controlled security mode, dedicated
      security mode, multilevel security mode, partitioned security
      mode, system-high security mode. Compare: protection level.)

      3. (I) /IKE/ IKE refers to its various types of ISAKMP-scripted
      exchanges of messages as "modes". Among these are the following:
      -  "Main mode": One of IKE's two phase 1 modes. (See: ISAKMP.)
      -  "Quick mode": IKE's only phase 2 mode. (See: ISAKMP.)

   $ model
      See: formal model, security model.

   $ modulus
      (I) The defining constant in modular arithmetic, and usually a
      part of the public key in asymmetric cryptography that is based on
      modular arithmetic. (See: Diffie-Hellman-Merkle, RSA.)

   $ Mondex
      (O) A smartcard-based electronic money system that incorporates
      cryptography and can be used to make payments via the Internet.
      (See: IOTP.)

   $ Morris Worm
      (I) A worm program that flooded the ARPANET in November 1988,
      causing problems for thousands of hosts. [R1135] (See: community
      risk, worm)

   $ MOSS
      (I) See: MIME Object Security Services.

   $ MQV
      (N) A key-agreement protocol [Mene] that was proposed by A.J.
      Menezes, M. Qu, and S.A. Vanstone in 1995 and is based on the
      Diffie-Hellman-Merkle algorithm.

   $ MSP
      (N) See: Message Security Protocol.

   $ multicast security
      See: secure multicast

   $ Multics
      (N) MULTiplexed Information and Computing Service, an MLS computer
      timesharing system designed and implemented during 1965-69 by a
      consortium including Massachusetts Institute of Technology,
      General Electric, and Bell Laboratories, and later offered
      commercially by Honeywell.

      Tutorial: Multics was one of the first large, general-purpose,
      operating systems to include security as a primary goal from the
      inception of the design and development and was rated in TCSEC
      Class B2. Its many innovative hardware and software security
      mechanisms (e.g., protection ring) were adopted by later systems.

   $ multilevel secure (MLS)
      (I) Describes an information system that is trusted to contain,
      and maintain separation between, resources (particularly stored
      data) of different security levels. (Examples: BLACKER, CANEWARE,
      KSOS, Multics, SCOMP.)

      Usage: Usually understood to mean that the system permits
      concurrent access by users who differ in their access
      authorizations, while denying users access to resources for which
      they lack authorization.

   $ multilevel security mode
      1. (N) A mode of system operation wherein (a) two or more security
      levels of information are allowed to be to be handled concurrently
      within the same system when some users having access to the system
      have neither a security clearance nor need-to-know for some of the
      data handled by the system and (b) separation of the users and the
      classified material on the basis, respectively, of clearance and
      classification level are dependent on operating system control.
      (See: /system operation/ under "mode", need to know, protection
      level, security clearance. Compare: controlled mode.)

      Usage: Usually abbreviated as "multilevel mode". This term was
      defined in U.S. Government policy regarding system accreditation,
      but the term is also used outside the Government.

      2. (O) A mode of system operation in which all three of the
      following statements are true: (a) Some authorized users do not
      have a security clearance for all the information handled in the
      system. (b) All authorized users have the proper security
      clearance and appropriate specific access approval for the
      information to which they have access. (c) All authorized users
      have a need-to-know only for information to which they have
      access. [C4009] (See: formal access approval, protection level.)

   $ Multipurpose Internet Mail Extensions (MIME)
      (I) An Internet protocol (RFC 2045) that enhances the basic format
      of Internet electronic mail messages (RFC 822) (a) to enable
      character sets other than U.S. ASCII to be used for textual
      headers and content and (b) to carry non-textual and multi-part
      content. (See: S/MIME.)

   $ mutual suspicion
      (I) The state that exists between two interacting system entities
      in which neither entity can trust the other to function correctly
      with regard to some security requirement.

   $ name
      (I) Synonym for "identifier".

   $ naming authority
      (O) /U.S. DoD/ An organizational entity responsible for assigning
      DNs and for assuring that each DN is meaningful and unique within
      its domain. [DoD9]

   $ National Computer Security Center (NCSC)
      (O) A U.S. DoD organization, housed in NSA, that has
      responsibility for encouraging widespread availability of trusted
      systems throughout the U.S. Federal Government. It has established
      criteria for, and performed evaluations of, computer and network
      systems that have a TCB. (See: Rainbow Series, TCSEC.)

   $ National Information Assurance Partnership (NIAP)
      (N) A joint initiative of NIST and NSA to enhance the quality of
      commercial products for information security and increase consumer
      confidence in those products through objective evaluation and
      testing methods.

      Tutorial: NIAP is registered, through the U.S. DoD, as a National
      Performance Review Reinvention Laboratory. NIAP functions include
      the following:
      -  Developing tests, test methods, and other tools that developers
         and testing laboratories may use to improve and evaluate
         security products.
      -  Collaborating with industry and others on research and testing
         programs.
      -  Using the Common Criteria to develop protection profiles and
         associated test sets for security products and systems.
      -  Cooperating with the NIST National Voluntary Laboratory
         Accreditation Program to develop a program to accredit private-
         sector laboratories for the testing of information security
         products using the Common Criteria.
      -  Working to establish a formal, international mutual recognition
         scheme for a Common Criteria-based evaluation.

   $ National Institute of Standards and Technology (NIST)
      (N) A U.S. Department of Commerce organization that promotes U.S.
      economic growth by working with industry to develop and apply
      technology, measurements, and standards. Has primary U.S.
      Government responsibility for INFOSEC standards for sensitive
      unclassified information. (See: ANSI, DES, DSA, DSS, FIPS, NIAP,
      NSA.)

   $ National Reliability and Interoperability Council (NRIC)
      (N) An advisory committee chartered by the U.S. Federal
      Communications Commission (FCC), with participation by network
      service providers and vendors, to provide recommendations to the
      FCC for assuring reliability, interoperability, robustness, and
      security of wireless, wireline, satellite, cable, and public data
      communication networks.

   $ national security
      (O) /U.S. Government/ The national defense or foreign relations of
      the United States of America.

   $ National Security Agency (NSA)
      (N) A U.S. DoD organization that has primary U.S. Government
      responsibility for INFOSEC standards for classified information
      and for sensitive unclassified information handled by national
      security systems. (See: FORTEZZA, KEA, MISSI, national security
      system, NIAP, NIST, SKIPJACK.)

   $ national security information
      (O) /U.S. Government/ Information that has been determined,
      pursuant to Executive Order 12958 or any predecessor order, to
      require protection against unauthorized disclosure. [C4009]

   $ national security system
      (O) /U.S. Government/ Any Government-operated information system
      for which the function, operation, or use (a) involves
      intelligence activities; (b) involves cryptologic activities
      related to national security; (c) involves command and control of
      military forces; (d) involves equipment that is an integral part
      of a weapon or weapon system; or (e) is critical to the direct
      fulfillment of military or intelligence missions and does not
      include a system that is to be used for routine administrative and
      business applications (including payroll, finance, logistics, and
      personnel management applications). [Title 40 U.S.C. Section 1552,
      Information Technology Management Reform Act of 1996.] (See: type
      2 product.)

   $ natural disaster
      (I) /threat action/ See: secondary definitions under "corruption"
      and "incapacitation".

   $ NCSC
      (O) See: National Computer Security Center.

   $ need to know, need-to-know
      (I) The necessity for access to, knowledge of, or possession of
      specific information required to carry out official duties.

      Usage: The compound "need-to-know" is commonly used as either an
      adjective or a noun.

      Tutorial: The need-to-know criterion is used in security
      procedures that require a custodian of sensitive information,
      prior to disclosing the information to someone else, to establish
      that the intended recipient has proper authorization to access the
      information.

   $ network
      (I) An information system comprised of a collection of
      interconnected nodes. (See: computer network.)

   $ Network Hardware Layer
      (I) See: Internet Protocol Suite.

   $ Network Interface Layer
      (I) See: Internet Protocol Suite.

   $ Network Layer Security Protocol (NLSP).
      (N) An OSI protocol (IS0 11577) for end-to-end encryption services
      at the top of OSIRM Layer 3. NLSP is derived from SP3 but is more
      complex. (Compare: IPsec.)

   $ Network Substrate Layer
      (I) Synonym for "Network Hardware Layer".

   $ network weaving
      (I) A penetration technique in which an intruder avoids detection
      and traceback by using multiple, linked, communication networks to
      access and attack a system. [C4009]

   $ NIAP
      (N) See: National Information Assurance Partnership.

   $ nibble
      (D) Half of a byte (i.e., usually, 4 bits).

      Deprecated Term: To avoid international misunderstanding, IDOCs
      SHOULD NOT use this term; instead, state the size of the block
      explicitly (e.g., "4-bit block"). (See: Deprecated Usage under
      "Green Book".)

   $ NIPRNET
      (O) The U.S. DoD's common-use Non-Classified Internet Protocol
      Router Network; the part of the Internet that is wholly controlled
      by the U.S. DoD and is used for official DoD business.

   $ NIST
      (N) See: National Institute of Standards and Technology.

   $ NLSP
      (N) See: Network Layer Security Protocol

   $ no-lone zone
      (I) A room or other space or area to which no person may have
      unaccompanied access and that, when occupied, is required to be
      occupied by two or more appropriately authorized persons. [C4009]
      (See: dual control.)

   $ no-PIN ORA (NORA)
      (O) /MISSI/ An organizational RA that operates in a mode in which
      the ORA performs no card management functions and, therefore, does
      not require knowledge of either the SSO PIN or user PIN for an end
      user's FORTEZZA PC card.

   $ node
      (I) A collection of related subsystems located on one or more
      computer platforms at a single site. (See: site.)

   $ nonce
      (I) A random or non-repeating value that is included in data
      exchanged by a protocol, usually for the purpose of guaranteeing
      liveness and thus detecting and protecting against replay attacks.
      (See: fresh.)

   $ non-critical
      See: critical.

   $ non-repudiation service
      1. (I) A security service that provide protection against false
      denial of involvement in an association (especially a
      communication association that transfers data). (See: repudiation,
      time stamp.)

      Tutorial: Two separate types of denial are possible -- an entity
      can deny that it sent a data object, or it can deny that it
      received a data object -- and, therefore, two separate types of
      non-repudiation service are possible. (See: non-repudiation with
      proof of origin, non-repudiation with proof of receipt.)

      2. (D) "Assurance [that] the sender of data is provided with proof
      of delivery and the recipient is provided with proof of the
      sender's identity, so neither can later deny having processed the
      data." [C4009]

      Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
      it bundles two security services -- non-repudiation with proof of
      origin, and non-repudiation with proof of receipt -- that can be
      provided independently of each other.

      Usage: IDOCs SHOULD distinguish between the technical aspects and
      the legal aspects of a non-repudiation service:
      -  "Technical non-repudiation": Refers to the assurance a relying
         party has that if a public key is used to validate a digital
         signature, then that signature had to have been made by the
         corresponding private signature key. [SP32]
      -  "Legal non-repudiation": Refers to how well possession or
         control of the private signature key can be established. [SP32]

      Tutorial: Non-repudiation service does not prevent an entity from
      repudiating a communication. Instead, the service provides
      evidence that can be stored and later presented to a third party
      to resolve disputes that arise if and when a communication is
      repudiated by one of the entities involved.

      Ford describes the six phases of a complete non-repudiation
      service and uses "critical action" to refer to the act of
      communication that is the subject of the service [For94, For97]:

      --------   --------   --------   --------   --------   . --------
      Phase 1:   Phase 2:   Phase 3:   Phase 4:   Phase 5:   . Phase 6:
      Request    Generate   Transfer   Verify     Retain     . Resolve
      Service    Evidence   Evidence   Evidence   Evidence   . Dispute
      --------   --------   --------   --------   --------   . --------

      Service    Critical   Evidence   Evidence   Archive    . Evidence
      Request => Action  => Stored  => Is      => Evidence   . Is
      Is Made    Occurs     For Later  Tested     In Case    . Verified
                 and        Use |          ^      Critical   .    ^
                 Evidence       v          |      Action Is  .    |
                 Is         +-------------------+ Repudiated .    |
                 Generated  |Verifiable Evidence|------> ... . ----+
                            +-------------------+

      Phase / Explanation
      -------------------
      1. Request service: Before the critical action, the service
         requester asks, either implicitly or explicitly, to have
         evidence of the action be generated.
      2. Generate evidence: When the critical action occurs, evidence is
         generated by a process involving the potential repudiator and
         possibly also a trusted third party.
      3. Transfer evidence: The evidence is transferred to the requester
         or stored by a third party, for later use (if needed).
      4. Verify evidence: The entity that holds the evidence tests it to
         be sure that it will suffice if a dispute arises.
      5. Retain evidence: The evidence is retained for possible future
         retrieval and use.
      6. Resolve dispute: In this phase, which occurs only if the
         critical action is repudiated, the evidence is retrieved from
         storage, presented, and verified to resolve the dispute.

   $ non-repudiation with proof of origin
      (I) A security service that provides the recipient of data with
      evidence that proves the origin of the data, and thus protects the
      recipient against an attempt by the originator to falsely deny
      sending the data. (See: non-repudiation service.)

      Tutorial: This service is a strong version of data origin
      authentication service. This service can not only verify the
      identity of a system entity that is the original source of
      received data; it can also provide proof of that identity to a
      third party.

   $ non-repudiation with proof of receipt
      (I) A security service that provides the originator of data with
      evidence that proves the data was received as addressed, and thus
      protects the originator against an attempt by the recipient to
      falsely deny receiving the data. (See: non-repudiation service.)

   $ non-volatile media
      (I) Storage media that, once written into, provide stable storage
      of information without an external power supply. (Compare:
      permanent storage, volatile media.)

   $ NORA
      (O) See: no-PIN ORA.

   $ notarization
      (I) Registration of data under the authority or in the care of a
      trusted third party, thus making it possible to provide subsequent
      assurance of the accuracy of characteristics claimed for the data,
      such as content, origin, time of existence, and delivery.
      [I7498-2] (See: digital notary.)

   $ NRIC
      (N) See: Network Reliability and Interoperability Council.

   $ NSA
      (N) See: National Security Agency

   $ null
      (N) /encryption/ "Dummy letter, letter symbol, or code group
      inserted into an encrypted message to delay or prevent its
      decryption or to complete encrypted groups for transmission or
      transmission security purposes." [C4009]

   $ NULL encryption algorithm
      (I) An algorithm [R2410] that is specified as doing nothing to
      transform plaintext data; i.e., a no-op. It originated because ESP
      always specifies the use of an encryption algorithm for
      confidentiality. The NULL encryption algorithm is a convenient way
      to represent the option of not applying encryption in ESP (or in
      any other context where a no-op is needed). (Compare: null.)

   $ OAKLEY
      (I) A key establishment protocol (proposed for IPsec but
      superseded by IKE) based on the Diffie-Hellman-Merkle algorithm
      and designed to be a compatible component of ISAKMP. [R2412]

      Tutorial: OAKLEY establishes a shared key with an assigned
      identifier and associated authenticated identities for parties;

      i.e., OAKLEY provides authentication service to ensure the
      entities of each other's identity, even if the Diffie-Hellman-
      Merkle exchange is threatened by active wiretapping. Also, it
      provides public-key forward secrecy for the shared key and
      supports key updates, incorporation of keys distributed by out-of-
      band mechanisms, and user-defined abstract group structures for
      use with Diffie-Hellman-Merkle.

   $ object
      (I) /formal model/ Trusted-system modeling usage: A system
      component that contains or receives information. (See: Bell-
      LaPadula model, object reuse, trusted system.)

   $ object identifier (OID)
      1. (N) An official, globally unique name for a thing, written as a
      sequence of integers (which are formed and assigned as defined in
      the ASN.1 standard) and used to reference the thing in abstract
      specifications and during negotiation of security services in a
      protocol.

      2. (O) "A value (distinguishable from all other such values)
      [that] is associated with an object." [X680]

      Tutorial: Objects named by OIDs are leaves of the object
      identifier tree (which is similar to but different from the X.500
      Directory Information Tree). Each arc (i.e., each branch of the
      tree) is labeled with a non-negative integer. An OID is the
      sequence of integers on the path leading from the root of the tree
      to a named object.

      The OID tree has three arcs immediately below the root: {0} for
      use by ITU-T, {1} for use by ISO, and {2} for use by both jointly.
      Below ITU-T are four arcs, where {0 0} is for ITU-T
      recommendations. Below {0 0} are 26 arcs, one for each series of
      recommendations starting with the letters A to Z, and below these
      are arcs for each recommendation. Thus, the OID for ITU-T
      Recommendation X.509 is {0 0 24 509}. Below ISO are four arcs,
      where {1 0 }is for ISO standards, and below these are arcs for
      each ISO standard. Thus, the OID for ISO/IEC 9594-8 (the ISO
      number for X.509) is {1 0 9594 8}.

      ANSI registers organization names below the branch {joint-iso-
      ccitt(2) country(16) US(840) organization(1) gov(101) csor(3)}.
      The NIST CSOR records PKI objects below the branch {joint-iso-itu-
      t(2) country(16) us(840) organization (1) gov(101) csor(3)}. The
      U.S. DoD registers INFOSEC objects below the branch {joint-iso-
      itu-t(2) country(16) us(840) organization(1) gov(101) dod(2)
      infosec(1)}.

      The IETF's Public-Key Infrastructure (pkix) Working Group
      registers PKI objects below the branch {iso(1) identified-
      organization(3) dod(6) internet(1) security(5) mechanisms(5)
      pkix(7)}. [R3280]

   $ object reuse
      (N) /COMPUSEC/ Reassignment and reuse of an area of a storage
      medium (e.g., random-access memory, floppy disk, magnetic tape)
      that once contained sensitive data objects. Before being
      reassigned for use by a new subject, the area needs to be erased
      or, in some cases, purged. [NCS04] (See: object.)

   $ obstruction
      (I) A type of threat action that interrupts delivery of system
      services by hindering system operations. (See: disruption.)

      Tutorial: This type of threat action includes the following
      subtypes:
      -  "Interference": Disruption of system operations by blocking
         communication of user data or control information. (See:
         jamming.)
      -  "Overload": Hindrance of system operation by placing excess
         burden on the performance capabilities of a system component.
         (See: flooding.)

   $ OCSP
      (I) See: Online Certificate Status Protocol.

   $ octet
      (I) A data unit of eight bits. (Compare: byte.)

      Usage: This term is used in networking (especially in OSI
      standards) in preference to "byte", because some systems use
      "byte" for data storage units of a size other than eight bits.

   $ OFB
      (N) See: output feedback.

   $ off-line attack
      (I) See: secondary definition under "attack".

   $ ohnosecond
      (D) That minuscule fraction of time in which you realize that your
      private key has been compromised.

      Deprecated Usage: IDOCs SHOULD NOT use this term; it is a joke for
      English speakers. (See: Deprecated Usage under "Green Book".)

   $ OID
      (N) See: object identifier.

   $ Online Certificate Status Protocol (OCSP)
      (I) An Internet protocol [R2560] used by a client to obtain from a
      server the validity status and other information about a digital
      certificate. (Mentioned in [X509] but not specified there.)

      Tutorial: In some applications, such as those involving high-value
      commercial transactions, it may be necessary either (a) to obtain
      certificate revocation status that is timelier than is possible
      with CRLs or (b) to obtain other kinds of status information. OCSP
      may be used to determine the current revocation status of a
      digital certificate, in lieu of or as a supplement to checking
      against a periodic CRL. An OCSP client issues a status request to
      an OCSP server and suspends acceptance of the certificate in
      question until the server provides a response.

   $ one-time pad
      1. (N) A manual encryption system in the form of a paper pad for
      one-time use.

      2. (I) An encryption algorithm in which the key is a random
      sequence of symbols and each symbol is used for encryption only
      one time -- i.e., used to encrypt only one plaintext symbol and
      thus produce only one ciphertext symbol -- and a copy of the key
      is used similarly for decryption.

      Tutorial: To ensure one-time use, the copy of the key used for
      encryption is destroyed after use, as is the copy used for
      decryption. This is the only encryption algorithm that is truly
      unbreakable, even given unlimited resources for cryptanalysis
      [Schn], but key management costs and synchronization problems make
      it impractical except in special situations.

   $ one-time password, One-Time Password (OTP)
      1. (I) /not capitalized/ A "one-time password" is a simple
      authentication technique in which each password is used only once
      as authentication information that verifies an identity. This
      technique counters the threat of a replay attack that uses
      passwords captured by wiretapping.

      2. (I) /capitalized/ "One-Time Password" is an Internet protocol
      [R2289] that is based on S/KEY and uses a cryptographic hash
      function to generate one-time passwords for use as authentication
      information in system login and in other processes that need
      protection against replay attacks.

   $ one-way encryption
      (I) Irreversible transformation of plain text to cipher text, such
      that the plain text cannot be recovered from the cipher text by
      other than exhaustive procedures even if the cryptographic key is
      known. (See: brute force, encryption.)

   $ one-way function
      (I) "A (mathematical) function, f, [that] is easy to compute, but
      which for a general value y in the range, it is computationally
      difficult to find a value x in the domain such that f(x) = y.
      There may be a few values of y for which finding x is not
      computationally difficult." [X509]

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      "cryptographic hash".

   $ onion routing
      (I) A system that can be used to provide both (a) data
      confidentiality and (b) traffic-flow confidentiality for network
      packets, and also provide (c) anonymity for the source of the
      packets.

      Tutorial: The source, instead of sending a packet directly to the
      intended destination, sends it to an "onion routing proxy" that
      builds an anonymous connection through several other "onion
      routers" to the destination. The proxy defines a route through the
      "onion routing network" by encapsulating the original payload in a
      layered data packet called an "onion", in which each layer defines
      the next hop in the route and each layer is also encrypted. Along
      the route, each onion router that receives the onion peels off one
      layer; decrypts that layer and reads from it the address of the
      next onion router on the route; pads the remaining onion to some
      constant size; and sends the padded onion to that next router.

   $ open security environment
      (O) /U.S. DoD/ A system environment that meets at least one of the
      following two conditions: (a) Application developers (including
      maintainers) do not have sufficient clearance or authorization to
      provide an acceptable presumption that they have not introduced
      malicious logic. (b) Configuration control does not provide
      sufficient assurance that applications and the equipment are
      protected against the introduction of malicious logic prior to and
      during the operation of system applications. [NCS04] (See: "first
      law" under "Courtney's laws". Compare: closed security
      environment.)

   $ open storage
      (N) /U.S. Government/ "Storage of classified information within an
      accredited facility, but not in General Services Administration
      approved secure containers, while the facility is unoccupied by
      authorized personnel." [C4009]

   $ Open Systems Interconnection (OSI) Reference Model (OSIRM)
      (N) A joint ISO/ITU-T standard [I7498-1] for a seven-layer,
      architectural communication framework for interconnection of
      computers in networks. (See: OSIRM Security Architecture. Compare:
      Internet Protocol Suite.)

      Tutorial: OSIRM-based standards include communication protocols
      that are mostly incompatible with the IPS, but also include
      security models, such as X.509, that are used in the Internet.

      The OSIRM layers, from highest to lowest, are (7) Application, (6)
      Presentation, (5) Session, (4) Transport, (3) Network, (2) Data
      Link, and (1) Physical.

      Usage: This Glossary refers to OSIRM layers by number to avoid
      confusing them with IPS layers, which are referred to by name.

      Some unknown person described how the OSIRM layers correspond to
      the seven deadly sins:

      7. Wrath: Application is always angry with the mess it sees below
         itself. (Hey! Who is it to be pointing fingers?)
      6. Sloth: Presentation is too lazy to do anything productive by
         itself.
      5. Lust: Session is always craving and demanding what truly
         belongs to Application's functionality.
      4. Avarice: Transport wants all of the end-to-end functionality.
         (Of course, it deserves it, but life isn't fair.)
      3. Gluttony: (Connection-Oriented) Network is overweight and
         overbearing after trying too often to eat Transport's lunch.
      2. Envy: Poor Data Link is always starved for attention. (With
         Asynchronous Transfer Mode, maybe now it is feeling less
         neglected.)
      1. Pride: Physical has managed to avoid much of the controversy,
         and nearly all of the embarrassment, suffered by the others.

      John G. Fletcher described how the OSIRM layers correspond to Snow
      White's dwarf friends:

7. Doc: Application acts as if it is in charge, but sometimes
muddles its syntax.

      6. Sleepy: Presentation is indolent, being guilty of the sin of
         Sloth.
      5. Dopey: Session is confused because its charter is not very
         clear.
      4. Grumpy: Transport is irritated because Network has encroached
         on Transport's turf.
      3. Happy: Network smiles for the same reason that Transport is
         irritated.
      2. Sneezy: Data Link makes loud noises in the hope of attracting
         attention.
      1. Bashful: Physical quietly does its work, unnoticed by the
         others.

   $ operational integrity
      (I) Synonym for "system integrity"; this synonym emphasizes the
      actual performance of system functions rather than just the
      ability to perform them.

   $ operational security
      1. (I) System capabilities, or performance of system functions,
      that are needed either (a) to securely manage a system or (b) to
      manage security features of a system. (Compare: operations
      security (OPSEC).)

      Usage: IDOCs that use this term SHOULD state a definition because
      (a) the definition provided here is general and vague and (b) the
      term could easily be confused with "operations security", which is
      a different concept.

      Tutorial: For example, in the context of an Internet service
      provider, the term could refer to capabilities to manage network
      devices in the event of attacks, simplify troubleshooting, keep
      track of events that affect system integrity, help analyze sources
      of attacks, and provide administrators with control over network
      addresses and protocols to help mitigate the most common attacks
      and exploits. [R3871]

      2. (D) Synonym for "administrative security".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "administrative security". Any type of security may affect
      system operations; therefore, the term may be misleading. Instead,
      use "administrative security", "communication security", "computer
      security", "emanations security", "personnel security", "physical
      security", or whatever specific type is meant. (See: security
      architecture. Compare: operational integrity, OPSEC.)

   $ operations security (OPSEC)
      (I) A process to identify, control, and protect evidence of the
      planning and execution of sensitive activities and operations, and
      thereby prevent potential adversaries from gaining knowledge of
      capabilities and intentions. (See: communications cover. Compare:
      operational security.)

   $ operator
      (I) A person who has been authorized to direct selected functions
      of a system. (Compare: manager, user.)

      Usage: IDOCs that use this term SHOULD state a definition for it
      because a system operator may or may not be treated as a "user".

   $ OPSEC
      1. (I) Abbreviation for "operations security".

      2. (D) Abbreviation for "operational security".

      Deprecated Usage: IDOCs SHOULD NOT use this abbreviation for
      "operational security" (as defined in this Glossary), because its
      use for "operations security" has been well established for many
      years, particular in the military community.

   $ ORA
      See: organizational registration authority.

   $ Orange Book
      (D) /slang/ Synonym for "Trusted Computer System Evaluation
      Criteria" [CSC1, DoD1].

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      "Trusted Computer System Evaluation Criteria" [CSC1, DoD1].
      Instead, use the full, proper name of the document or, in
      subsequent references, the abbreviation "TCSEC". (See: Deprecated
      Usage under "Green Book".)

   $ organizational certificate
      1. (I) An X.509 public-key certificate in which the "subject"
      field contains the name of an institution or set (e.g., a
      business, government, school, labor union, club, ethnic group,
      nationality, system, or group of individuals playing the same
      role), rather than the name of an individual person or device.
      (Compare: persona certificate, role certificate.)

      Tutorial: Such a certificate might be issued for one of the
      following purposes:

      -  To enable an individual to prove membership in the
         organization.
      -  To enable an individual to represent the organization, i.e., to
         act in its name and with its powers or permissions.

      2. (O) /MISSI/ A type of MISSI X.509 public-key certificate that
      is issued to support organizational message handling for the U.S.
      DoD's Defense Message System.

   $ organizational registration authority (ORA)
      1. (I) /PKI/ An RA for an organization.

      2. (O) /MISSI/ An end entity that (a) assists a PCA, CA, or SCA to
      register other end entities, by gathering, verifying, and entering
      data and forwarding it to the signing authority and (b) may also
      assist with card management functions. An ORA is a local
      administrative authority, and the term refers both to the role and
      to the person who plays that role. An ORA does not sign
      certificates, CRLs, or CKLs. (See: no-PIN ORA, SSO-PIN ORA, user-
      PIN ORA.)

   $ origin authentication
      (D) Synonym for "data origin authentication". (See:
      authentication, data origin authentication.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
      careless use of the internationally standardized term "data origin
      authentication" and also could be confused with "peer entity
      authentication."

   $ origin authenticity
      (D) Synonym for "data origin authentication". (See: authenticity,
      data origin authentication.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it suggests
      careless use of the internationally standardized term "data origin
      authentication" and mixes concepts in a potentially misleading
      way.

   $ OSI, OSIRM
      (N) See: Open Systems Interconnection Reference Model.

   $ OSIRM Security Architecture
      (N) The part of the OSIRM [I7498-2] that specifies the security
      services and security mechanisms that can be applied to protect
      communications between two systems. (See: security architecture.)

      Tutorial: This part of the OSIRM includes an allocation of
      security services to protocol layers. The following table shows
      which security services (see definitions in this Glossary) are
      permitted by the OSIRM in each of its layers. (Also, an
      application process that operates above the Application Layer may
      itself provide security services.) Similarly, the table suggests
      which services are suitable for each IPS layer. However,
      explaining and justifying these allocations is beyond the scope of
      this Glossary.

      Legend for Table Entries:
         O = Yes, [I7498-2] permits the service in this OSIRM layer.
         I = Yes, the service can be incorporated in this IPS layer.
         * = This layer subsumed by Application Layer in IPS.

      IPS Protocol Layers    +-----------------------------------------+
                             |Network| Net |In-| Trans |  Application  |
                             |  H/W  |Inter|ter| -port |               |
                             |       |-face|net|       |               |
      OSIRM Protocol Layers  +-----------------------------------------+
                             |  1  |  2  |  3  |  4  |  5  |  6  |  7  |
      Confidentiality        +-----------------------------------------+
      -  Datagram            | O I | O I | O I | O I |     | O * | O I |
      -  Selective Field     |     |     |   I |     |     | O * | O I |
      -  Traffic Flow        | O   |     | O   |     |     |     | O   |
         -- Full             |   I |     |     |     |     |     |     |
         -- Partial          |     |   I |   I |     |     |     |   I |
      Integrity              +-----------------------------------------+
      -  Datagram            |   I |   I | O I | O I |     |     | O I |
      -  Selective Field     |     |     |   I |     |     |     | O I |
      -  Stream              |     |     | O I | O I |     |     | O I |
      Authentication         +-----------------------------------------+
      -  Peer Entity         |     |   I | O I | O I |     |     | O I |
      -  Data Origin         |     |   I | O I | O I |     |     | O I |
      Access Control         +-----------------------------------------+
      -  type as appropriate |     |   I | O I | O I |     |     | O I |
      Non-Repudiation        +-----------------------------------------+
      -  of Origin           |     |     |     |     |     |     | O I |
      -  of Receipt          |     |     |     |     |     |     | O I |
                             +-----------------------------------------+

   $ OTAR
      (N) See: over-the-air rekeying.

   $ OTP
      (I) See: One-Time Password.

   $ out-of-band
      (I) /adjective, adverb/ Information transfer using a channel or
      method that is outside (i.e., separate from or different from) the
      main channel or normal method.

      Tutorial: Out-of-band mechanisms are often used to distribute
      shared secrets (e.g., a symmetric key) or other sensitive
      information items (e.g., a root key) that are needed to initialize
      or otherwise enable the operation of cryptography or other
      security mechanisms. Example: Using postal mail to distribute
      printed or magnetic media containing symmetric cryptographic keys
      for use in Internet encryption devices. (See: key distribution.)

   $ output feedback (OFB)
      (N) A block cipher mode that modifies ECB mode to operate on
      plaintext segments of variable length less than or equal to the
      block length. [FP081] (See: block cipher, [SP38A].)

      Tutorial: This mode operates by directly using the algorithm's
      previously generated output block as the algorithm's next input
      block (i.e., by "feeding back" the output block) and combining
      (exclusive OR-ing) the output block with the next plaintext
      segment (of block length or less) to form the next ciphertext
      segment.

   $ outside attack
      (I) See: secondary definition under "attack". Compare: outsider.)

   $ outsider
      (I) A user (usually a person) that accesses a system from a
      position that is outside the system's security perimeter.
      (Compare: authorized user, insider, unauthorized user.)

      Tutorial: The actions performed by an outsider in accessing the
      system may be either authorized or unauthorized; i.e., an outsider
      may act either as an authorized user or as an unauthorized user.

   $ over-the-air rekeying (OTAR)
      (N) Changing a key in a remote cryptographic device by sending a
      new key directly to the device via a channel that the device is
      protecting. [C4009]

   $ overload
      (I) /threat action/ See: secondary definition under "obstruction".

   $ P1363
      (N) See: IEEE P1363.

   $ PAA
      (O) See: policy approving authority.

   $ package
      (N) /Common Criteria/ A reusable set of either functional or
      assurance components, combined in a single unit to satisfy a set
      of identified security objectives. (Compare: protection profile.)

      Example: The seven EALs defined in Part 3 of the Common Criteria
      are predefined assurance packages.

      Tutorial: A package is a combination of security requirement
      components and is intended to be reusable in the construction of
      either more complex packages or protection profiles and security
      targets. A package expresses a set of either functional or
      assurance requirements that meet some particular need, expressed
      as a set of security objectives.

   $ packet
      (I) A block of data that is carried from a source to a destination
      through a communication channel or, more generally, across a
      network. (Compare: datagram, PDU.)

   $ packet filter
      (I) See: secondary definition under "filtering router".

   $ packet monkey
      (D) /slang/ Someone who floods a system with packets, creating a
      denial-of-service condition for the system's users. (See:
      cracker.)

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ pagejacking
      (D) /slang/ A contraction of "Web page hijacking". A masquerade
      attack in which the attacker copies (steals) a home page or other
      material from the target server, rehosts the page on a server the
      attacker controls, and causes the rehosted page to be indexed by
      the major Web search services, thereby diverting browsers from the
      target server to the attacker's server.

      Deprecated Term: IDOCs SHOULD NOT use this contraction. The term
      is not listed in most dictionaries and could confuse international
      readers. (See: Deprecated Usage under "Green Book".)

   $ PAN
      (O) See: primary account number.

   $ PAP
      (I) See: Password Authentication Protocol.

   $ parity bit
      (I) A checksum that is computed on a block of bits by computing
      the binary sum of the individual bits in the block and then
      discarding all but the low-order bit of the sum. (See: checksum.)

   $ partitioned security mode
      (N) A mode of system operation wherein all users having access to
      the system have the necessary security clearances for all data
      handled by the system, but some users might not have either formal
      access approval or need-to-know for all the data. (See: /system
      operation/ under "mode", formal access approval, need to know,
      protection level, security clearance.)

      Usage: Usually abbreviated as "partitioned mode". This term was
      defined in U.S. Government policy on system accreditation.

   $ PASS
      (N) See: personnel authentication system string.

   $ passive attack
      (I) See: secondary definition under "attack".

   $ passive user
      (I) See: secondary definition under "system user".

   $ passive wiretapping
      (I) A wiretapping attack that attempts only to observe a
      communication flow and gain knowledge of the data it contains, but
      does not alter or otherwise affect that flow. (See: wiretapping.
      Compare: passive attack, active wiretapping.)

   $ password
      1a. (I) A secret data value, usually a character string, that is
      presented to a system by a user to authenticate the user's
      identity. (See: authentication information, challenge-response,
      PIN, simple authentication.)

      1b. (O) "A character string used to authenticate an identity."
      [CSC2]

      1c. (O) "A string of characters (letters, numbers, and other
      symbols) used to authenticate an identity or to verify access
      authorization." [FP140]

      1d. (O) "A secret that a claimant memorizes and uses to
      authenticate his or her identity. Passwords are typically
      character strings." [SP63]

      Tutorial: A password is usually paired with a user identifier that
      is explicit in the authentication process, although in some cases
      the identifier may be implicit. A password is usually verified by
      matching it to a stored value held by the access control system
      for that identifier.

      Using a password as authentication information is based on
      assuming that the password is known only by the system entity for
      which the identity is being authenticated. Therefore, in a network
      environment where wiretapping is possible, simple authentication
      that relies on transmission of static (i.e., repetitively used)
      passwords in cleartext form is inadequate. (See: one-time
      password, strong authentication.)

   $ Password Authentication Protocol (PAP)
      (I) A simple authentication mechanism in PPP. In PAP, a user
      identifier and password are transmitted in cleartext form. [R1334]
      (See: CHAP.)

   $ password sniffing
      (D) /slang/ Passive wiretapping to gain knowledge of passwords.
      (See: Deprecated Usage under "sniffing".)

   $ path discovery
      (I) For a digital certificate, the process of finding a set of
      public-key certificates that comprise a certification path from a
      trusted key to that specific certificate.

   $ path validation
      (I) The process of validating (a) all of the digital certificates
      in a certification path and (b) the required relationships between
      those certificates, thus validating the contents of the last
      certificate on the path. (See: certificate validation.)

      Tutorial: To promote interoperable PKI applications in the
      Internet, RFC 3280 specifies a detailed algorithm for validation
      of a certification path.

   $ payment card
      (N) /SET/ Collectively refers "to credit cards, debit cards,
      charge cards, and bank cards issued by a financial institution and
      which reflects a relationship between the cardholder and the
      financial institution." [SET2]

   $ payment gateway
      (O) /SET/ A system operated by an acquirer, or a third party
      designated by an acquirer, to provide electronic commerce services
      to the merchants in support of the acquirer, and which interfaces
      to the acquirer to support the authorization, capture, and
      processing of merchant payment messages, including payment
      instructions from cardholders. [SET1, SET2]

   $ payment gateway certification authority (SET PCA)
      (O) /SET/ A CA that issues digital certificates to payment
      gateways and is operated on behalf of a payment card brand, an
      acquirer, or another party according to brand rules. A SET PCA
      issues a CRL for compromised payment gateway certificates. [SET2]
      (See: PCA.)

   $ PC card
      (N) A type of credit card-sized, plug-in peripheral device that
      was originally developed to provide memory expansion for portable
      computers, but is also used for other kinds of functional
      expansion. (See: FORTEZZA, PCMCIA.)

      Tutorial: The international PC Card Standard defines a non-
      proprietary form factor in three sizes -- Types I, II, and III --
      each of which have a 68-pin interface between the card and the
      socket into which it plugs. All three types have the same length
      and width, roughly the size of a credit card, but differ in their
      thickness from 3.3 to 10.5 mm. Examples include storage modules,
      modems, device interface adapters, and cryptographic modules.

   $ PCA
      (D) Abbreviation of various kinds of "certification authority".
      (See: Internet policy certification authority, (MISSI) policy
      creation authority, (SET) payment gateway certification
      authority.)

      Deprecated Usage: An IDOC that uses this abbreviation SHOULD
      define it at the point of first use.

   $ PCI
      (N) See: "protocol control information" under "protocol data
      unit".

   $ PCMCIA
      (N) Personal Computer Memory Card International Association, a
      group of manufacturers, developers, and vendors, founded in 1989
      to standardize plug-in peripheral memory cards for personal
      computers and now extended to deal with any technology that works
      in the PC Card form factor. (See: PC card.)

   $ PDS
      (N) See: protective distribution system.

   $ PDU
      (N) See: protocol data unit.

   $ peer entity authentication
      (I) "The corroboration that a peer entity in an association is the
      one claimed." [I7498-2] (See: authentication.)

   $ peer entity authentication service
      (I) A security service that verifies an identity claimed by or for
      a system entity in an association. (See: authentication,
      authentication service.)

      Tutorial: This service is used at the establishment of, or at
      times during, an association to confirm the identity of one entity
      to another, thus protecting against a masquerade by the first
      entity. However, unlike data origin authentication service, this
      service requires an association to exist between the two entities,
      and the corroboration provided by the service is valid only at the
      current time that the service is provided. (See: "relationship
      between data integrity service and authentication services" under
      "data integrity service").

   $ PEM
      (I) See: Privacy Enhanced Mail.

   $ penetrate
      1a. (I) Circumvent a system's security protections. (See: attack,
      break, violation.)

      1b. (I) Successfully and repeatedly gain unauthorized access to a
      protected system resource. [Huff]

   $ penetration
      (I) /threat action/ See: secondary definition under "intrusion".

   $ penetration test
      (I) A system test, often part of system certification, in which
      evaluators attempt to circumvent the security features of a
      system. [NCS04, SP42] (See: tiger team.)

      Tutorial: Penetration testing evaluates the relative vulnerability
      of a system to attacks and identifies methods of gaining access to
      a system by using tools and techniques that are available to
      adversaries. Testing may be performed under various constraints
      and conditions, including a specified level of knowledge of the
      system design and implementation. For a TCSEC evaluation, testers
      are assumed to have all system design and implementation
      documentation, including source code, manuals, and circuit
      diagrams, and to work under no greater constraints than those
      applied to ordinary users.

   $ perfect forward secrecy
      (I) For a key agreement protocol, the property that compromises
      long-term keying material does not compromise session keys that
      were previously derived from the long-term material. (Compare:
      public-key forward secrecy.)

      Usage: Some existing RFCs use this term but either do not define
      it or do not define it precisely. While preparing this Glossary,
      we found this to be a muddled area. Experts did not agree. For all
      practical purposes, the literature defines "perfect forward
      secrecy" by stating the Diffie-Hellman-Merkle algorithm. The term
      "public-key forward secrecy" (suggested by Hilarie Orman) and the
      definition stated for it in this Glossary were crafted to be
      compatible with current Internet documents, yet be narrow and
      leave room for improved terminology.

      Challenge to the Internet security community: We need a taxonomy
      of terms and definitions to cover the basic properties discussed
      here for the full range of cryptographic algorithms and protocols
      used in Internet Standards:

      Involvement of session keys vs. long-term keys: Experts disagree
      about the basic ideas involved:
      -  One concept of "forward secrecy" is that, given observations of
         the operation of a key establishment protocol up to time t, and
         given some of the session keys derived from those protocol
         runs, you cannot derive unknown past session keys or future
         session keys.
      -  A related property is that, given observations of the protocol
         and knowledge of the derived session keys, you cannot derive
         one or more of the long-term private keys.

      -  The "I" definition presented above involves a third concept of
         "forward secrecy" that refers to the effect of the compromise
         of long-term keys.
      -  All three concepts involve the idea that a compromise of "this"
         encryption key is not supposed to compromise the "next" one.
         There also is the idea that compromise of a single key will
         compromise only the data protected by the single key. In
         Internet literature, the focus has been on protection against
         decryption of back traffic in the event of a compromise of
         secret key material held by one or both parties to a
         communication.

      Forward vs. backward: Experts are unhappy with the word "forward",
      because compromise of "this" encryption key also is not supposed
      to compromise the "previous" one, which is "backward" rather than
      forward. In S/KEY, if the key used at time t is compromised, then
      all keys used prior to that are compromised. If the "long-term"
      key (i.e., the base of the hashing scheme) is compromised, then
      all keys past and future are compromised; thus, you could say that
      S/KEY has neither forward nor backward secrecy.

      Asymmetric cryptography vs. symmetric: Experts disagree about
      forward secrecy in the context of symmetric cryptographic systems.
      In the absence of asymmetric cryptography, compromise of any long-
      term key seems to compromise any session key derived from the
      long-term key. For example, Kerberos isn't forward secret, because
      compromising a client's password (thus compromising the key shared
      by the client and the authentication server) compromises future
      session keys shared by the client and the ticket-granting server.

      Ordinary forward secrecy vs. "perfect" forward secret: Experts
      disagree about the difference between these two. Some say there is
      no difference, and some say that the initial naming was
      unfortunate and suggest dropping the word "perfect". Some suggest
      using "forward secrecy" for the case where one long-term private
      key is compromised, and adding "perfect" for when both private
      keys (or, when the protocol is multi-party, all private keys) are
      compromised.

      Acknowledgements: Bill Burr, Burt Kaliski, Steve Kent, Paul Van
      Oorschot, Jonathan Trostle, Michael Wiener, and, especially,
      Hilarie Orman contributed ideas to this discussion.

   $ perimeter
      See: security perimeter.

   $ periods processing
      (I) A mode of system operation in which information of different
      sensitivities is processed at distinctly different times by the
      same system, with the system being properly purged or sanitized
      between periods. (See: color change.)

      Tutorial: The security mode of operation and maximum
      classification of data handled by the system is established for an
      interval of time and then is changed for the following interval of
      time. A period extends from the secure initialization of the
      system to the completion of any purging of sensitive data handled
      by the system during the period.

   $ permanent storage
      (I) Non-volatile media that, once written into, can never be
      completely erased.

   $ permission
      1a. (I) Synonym for "authorization". (Compare: privilege.)

      1b. (N) An authorization or set of authorizations to perform
      security-relevant functions in the context of role-based access
      control. [ANSI]

      Tutorial: A permission is a positively stated authorization for
      access that (a) can be associated with one or more roles and (b)
      enables a user in a role to access a specified set of system
      resources by causing a specific set of system actions to be
      performed on the resources.

   $ persona certificate
      (I) An X.509 certificate issued to a system entity that wishes to
      use a persona to conceal its true identity when using PEM or other
      Internet services that depend on PKI support. (See: anonymity.)
      [R1422]

      Tutorial: PEM designers intended that (a) a CA issuing persona
      certificates would explicitly not be vouching for the identity of
      the system entity to whom the certificate is issued, (b) such
      certificates would be issued only by CAs subordinate to a policy
      CA having a policy stating that purpose (i.e., that would warn
      relying parties that the "subject" field DN represented only a
      persona and not a true, vetted user identity), and (c) the CA
      would not need to maintain records binding the true identity of
      the subject to the certificate.

      However, the PEM designers also intended that a CA issuing persona
      certificates would establish procedures (d) to enable "the holder
      of a PERSONA certificate to request that his certificate be
      revoked" and (e) to ensure that it did not issue the same subject
      DN to multiple users. The latter condition implies that a persona
      certificate is not an organizational certificate unless the
      organization has just one member or representative.

   $ personal identification number (PIN)
      1a. (I) A character string used as a password to gain access to a
      system resource. (See: authentication information.)

      Example: A cryptographic token typically requires its user to
      enter a PIN in order to access information stored in the token and
      invoke the token's cryptographic functions.

      1b. (O) An alphanumeric code or password used to authenticate an
      identity.

      Tutorial: Despite the words "identification" and "number", a PIN
      seldom serves as a user identifier, and a PIN's characters are not
      necessarily all numeric. Retail banking applications use 4-digit
      numeric user PINs, but the FORTEZZA PC card uses 12-character
      alphanumeric SSO PINs. (See: SSO PIN, user PIN.)

      A better name for this concept would have been "personnel
      authentication system string" (PASS), in which case, an
      alphanumeric character string for this purpose would have been
      called, obviously, a "PASSword".

   $ personal information
      (I) Information about a particular person, especially information
      of an intimate or critical nature, that could cause harm or pain
      to that person if disclosed to unauthorized parties. Examples:
      medical record, arrest record, credit report, academic transcript,
      training report, job application, credit card number, Social
      Security number. (See: privacy.)

   $ personality
      1. (I) Synonym for "principal".

      2. (O) /MISSI/ A set of MISSI X.509 public-key certificates that
      have the same subject DN, together with their associated private
      keys and usage specifications, that is stored on a FORTEZZA PC
      card to support a role played by the card's user.

      Tutorial: When a card's user selects a personality to use in a
      FORTEZZA-aware application, the data determines behavior traits

      (the personality) of the application. A card's user may have
      multiple personalities on the card. Each has a "personality
      label", a user-friendly character string that applications can
      display to the user for selecting or changing the personality to
      be used. For example, a military user's card might contain three
      personalities: GENERAL HALFTRACK, COMMANDER FORT SWAMPY, and NEW
      YEAR'S EVE PARTY CHAIRMAN. Each personality includes one or more
      certificates of different types (such as DSA versus RSA), for
      different purposes (such as digital signature versus encryption),
      or with different authorizations.

   $ personnel authentication system string (PASS)
      (N) See: Tutorial under "personal identification number".

   $ personnel security
      (I) Procedures to ensure that persons who access a system have
      proper clearance, authorization, and need-to-know as required by
      the system's security policy. (See: security architecture.)

   $ PGP(trademark)
      (O) See: Pretty Good Privacy(trademark).

   $ phase 1 negotiation
   $ phase 2 negotiation
      (I) /ISAKMP/ See: secondary definition under "Internet Security
      Association and Key Management Protocol".

   $ phishing
      (D) /slang/ A technique for attempting to acquire sensitive data,
      such as bank account numbers, through a fraudulent solicitation in
      email or on a Web site, in which the perpetrator masquerades as a
      legitimate business or reputable person. (See: social
      engineering.)

      Derivation: Possibly from "phony fishing"; the solicitation
      usually involves some kind of lure or bait to hook unwary
      recipients. (Compare: phreaking.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it is not listed
      in most dictionaries and could confuse international readers.
      (See: Deprecated Usage under "Green Book".)

   $ Photuris
      (I) A UDP-based, key establishment protocol for session keys,
      designed for use with the IPsec protocols AH and ESP. Superseded
      by IKE.

   $ phreaking
      (D) A contraction of "telephone breaking". An attack on or
      penetration of a telephone system or, by extension, any other
      communication or information system. [Raym]

      Deprecated Term: IDOCs SHOULD NOT use this contraction; it is not
      listed in most dictionaries and could confuse international
      readers. (See: Deprecated Usage under "Green Book".)

   $ physical destruction
      (I) /threat action/ See: secondary definition under
      "incapacitation".

   $ physical security
      (I) Tangible means of preventing unauthorized physical access to a
      system. Examples: Fences, walls, and other barriers; locks, safes,
      and vaults; dogs and armed guards; sensors and alarm bells.
      [FP031, R1455] (See: security architecture.)

   $ piggyback attack
      (I) A form of active wiretapping in which the attacker gains
      access to a system via intervals of inactivity in another user's
      legitimate communication connection. Sometimes called a "between-
      the-lines" attack. (See: hijack attack, man-in-the-middle attack.)

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the term could confuse international
      readers.

   $ PIN
      (I) See: personal identification number.

   $ ping of death
      (D) A denial-of-service attack that sends an improperly large ICMP
      echo request packet (a "ping") with the intent of causing the
      destination system to fail. (See: ping sweep, teardrop.)

      Deprecated Term: IDOCs SHOULD NOT use this term; instead, use
      "ping packet overflow attack" or some other term that is specific
      with regard to the attack mechanism.

      Tutorial: This attack seeks to exploit an implementation
      vulnerability. The IP specification requires hosts to be prepared
      to accept datagrams of up to 576 octets, but also permits IP
      datagrams to be up to 65,535 octets long. If an IP implementation
      does not properly handle very long IP packets, the ping packet may
      overflow the input buffer and cause a fatal system error.

   $ ping sweep
      (I) An attack that sends ICMP echo requests ("pings") to a range
      of IP addresses, with the goal of finding hosts that can be probed
      for vulnerabilities. (See: ping of death. Compare: port scan.)

   $ PKCS
      (N) See: Public-Key Cryptography Standards.

   $ PKCS #5
      (N) A standard [PKC05] (see: RFC 2898) from the PKCS series;
      defines a method for encrypting an octet string with a secret key
      derived from a password.

      Tutorial: Although the method can be used for arbitrary octet
      strings, its intended primary application in public-key
      cryptography is for encrypting private keys when transferring them
      from one computer system to another, as described in PKCS #8.

   $ PKCS #7
      (N) A standard [PKC07] (see: RFC 2315) from the PKCS series;
      defines a syntax for data that may have cryptography applied to
      it, such as for digital signatures and digital envelopes. (See:
      CMS.)

   $ PKCS #10
      (N) A standard [PKC10] (see: RFC 2986) from the PKCS series;
      defines a syntax for certification requests. (See: certification
      request.)

      Tutorial: A PKCS #10 request contains a DN and a public key, and
      may contain other attributes, and is signed by the entity making
      the request. The request is sent to a CA, who converts it to an
      X.509 public-key certificate (or some other form), and returns it,
      possibly in PKCS #7 format.

   $ PKCS #11
      (N) A standard [PKC11] from the PKCS series; defines CAPI called
      "Cryptoki" for devices that hold cryptographic information and
      perform cryptographic functions.

   $ PKI
      (I) See: public-key infrastructure.

   $ PKINIT
      (I) Abbreviation for "Public Key Cryptography for Initial
      Authentication in Kerberos" (RFC 4556). (See: Tutorial under
      "Kerberos".)

   $ PKIX
      1a. (I) A contraction of "Public-Key Infrastructure (X.509)", the
      name of the IETF working group that is specifying an architecture
      [R3280] and set of protocols [R4210] to provide X.509-based PKI
      services for the Internet.

      1b. (I) A collective name for that Internet PKI architecture and
      associated set of protocols.

      Tutorial: The goal of PKIX is to facilitate the use of X.509
      public-key certificates in multiple Internet applications and to
      promote interoperability between different implementations that
      use those certificates. The resulting PKI is intended to provide a
      framework that supports a range of trust and hierarchy
      environments and a range of usage environments. PKIX specifies (a)
      profiles of the v3 X.509 public-key certificate standards and the
      v2 X.509 CRL standards for the Internet, (b) operational protocols
      used by relying parties to obtain information such as certificates
      or certificate status, (c) management protocols used by system
      entities to exchange information needed for proper management of
      the PKI, and (d) information about certificate policies and CPSs,
      covering the areas of PKI security not directly addressed in the
      rest of PKIX.

   $ plain text
      1. (I) /noun/ Data that is input to an encryption process. (See:
      plaintext. Compare: cipher text, clear text.)

      2. (D) /noun/ Synonym for "clear text".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "clear text". Sometimes plain text that is input to an
      encryption operation is clear text, but other times plain text is
      cipher text that was output from a previous encryption operation.
      (See: superencryption.)

   $ plaintext
      1. (O) /noun/ Synonym for "plain text".

      2. (I) /adjective/ Referring to plain text. Usage: Commonly used
      instead of "plain-text". (Compare: ciphertext, cleartext.)

      3. (D) /noun/ Synonym for "cleartext".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "cleartext". Cleartext data is, by definition, not encrypted;
      but plaintext data that is input to an encryption operation may be

      cleartext data or may be ciphertext data that was output from a
      previous encryption operation. (See: superencryption.)

   $ PLI
      (I) See: Private Line Interface.

   $ PMA
      (N) See: policy management authority.

   $ Point-to-Point Protocol (PPP)
      (I) An Internet Standard protocol (RFC 1661) for encapsulation and
      full-duplex transportation of protocol data packets in OSIRM Layer
      3 over an OSIRM Layer 2 link between two peers, and for
      multiplexing different Layer 3 protocols over the same link.
      Includes optional negotiation to select and use a peer entity
      authentication protocol to authenticate the peers to each other
      before they exchange Layer 3 data. (See: CHAP, EAP, PAP.)

   $ Point-to-Point Tunneling Protocol (PPTP)
      (I) An Internet client-server protocol (RFC 2637) (originally
      developed by Ascend and Microsoft) that enables a dial-up user to
      create a virtual extension of the dial-up link across a network by
      tunneling PPP over IP. (See: L2TP.)

      Tutorial: PPP can encapsulate any IPS Network Interface Layer
      protocol or OSIRM Layer 3 protocol. Therefore, PPTP does not
      specify security services; it depends on protocols above and below
      it to provide any needed security. PPTP makes it possible to
      divorce the location of the initial dial-up server (i.e., the PPTP
      Access Concentrator, the client, which runs on a special-purpose
      host) from the location at which the dial-up protocol (PPP)
      connection is terminated and access to the network is provided
      (i.e., at the PPTP Network Server, which runs on a general-purpose
      host).

   $ policy
      1a. (I) A plan or course of action that is stated for a system or
      organization and is intended to affect and direct the decisions
      and deeds of that entity's components or members. (See: security
      policy.)

      1b. (O) A definite goal, course, or method of action to guide and
      determine present and future decisions, that is implemented or
      executed within a particular context, such as within a business
      unit. [R3198]

      Deprecated Abbreviation: IDOCs SHOULD NOT use "policy" as an
      abbreviation of either "security policy" or "certificate policy".

      Instead, to avoid misunderstanding, use a fully qualified term, at
      least at the point of first usage.

      Tutorial: The introduction of new technology to replace
      traditional systems can result in new systems being deployed
      without adequate policy definition and before the implications of
      the new technology are fully understand. In some cases, it can be
      difficult to establish policies for new technology before the
      technology has been operationally tested and evaluated. Thus,
      policy changes tend to lag behind technological changes, such that
      either old policies impede the technical innovation, or the new
      technology is deployed without adequate policies to govern its
      use.

      When new technology changes the ways that things are done, new
      "procedures" must be defined to establish operational guidelines
      for using the technology and achieving satisfactory results, and
      new "practices" must be established for managing new systems and
      monitoring results. Practices and procedures are more directly
      coupled to actual systems and business operations than are
      polices, which tend to be more abstract.
      -  "Practices" define how a system is to be managed and what
         controls are in place to monitor the system and detect abnormal
         behavior or quality problems. Practices are established to
         ensure that a system is managed in compliance with stated
         policies. System audits are primarily concerned with whether or
         not practices are being followed. Auditors evaluate the
         controls to make sure they conform to accepted industry
         standards, and then confirm that controls are in place and that
         control measurements are being gathered. Audit trails are
         examples of control measurements that are recorded as part of
         system operations.
      -  "Procedures" define how a system is operated, and relate
         closely to issues of what technology is used, who the operators
         are, and how the system is deployed physically. Procedures
         define both normal and abnormal operating circumstances.
      -  For every control defined by a practice statement, there should
         be corresponding procedures to implement the control and
         provide ongoing measurement of the control parameters.
         Conversely, procedures require management practices to insure
         consistent and correct operational behavior.

   $ policy approval authority
      (D) /PKI/ Synonym for "policy management authority". [PAG]

      Deprecated Term: IDOCs SHOULD NOT use this term as synonym for
      "policy management authority". The term suggests a limited,
      passive role that is not typical of PMAs.

   $ policy approving authority (PAA)
      (O) /MISSI/ The top-level signing authority of a MISSI
      certification hierarchy. The term refers both to that
      authoritative office or role and to the person who plays that
      role. (See: policy management authority, root registry.)

      Tutorial: A MISSI PAA (a) registers MISSI PCAs and signs their
      X.509 public-key certificates, (b) issues CRLs but does not issue
      a CKL, and (c) may issue cross-certificates to other PAAs.

   $ policy authority
      (D) /PKI/ Synonym for "policy management authority". [PAG]

      Deprecated Term: IDOCs SHOULD NOT use this term as synonym for
      "policy management authority". The term is unnecessarily vague and
      thus may be confused with other PKI entities, such as CAs and RAs,
      that enforce of apply various aspects of PKI policy.

   $ policy certification authority (Internet PCA)
      (I) An X.509-compliant CA at the second level of the Internet
      certification hierarchy, under the IPRA. Each PCA operates under
      its published security policy (see: certificate policy, CPS) and
      within constraints established by the IPRA for all PCAs. [R1422].
      (See: policy creation authority.)

   $ policy creation authority (MISSI PCA)
      (O) /MISSI/ The second level of a MISSI certification hierarchy;
      the administrative root of a security policy domain of MISSI users
      and other, subsidiary authorities. The term refers both to that
      authoritative office or role and to the person who fills that
      office. (See: policy certification authority.)

      Tutorial: A MISSI PCA's certificate is issued by a PAA. The PCA
      registers the CAs in its domain, defines their configurations, and
      issues their X.509 public-key certificates. (The PCA may also
      issue certificates for SCAs, ORAs, and other end entities, but a
      PCA does not usually do this.) The PCA periodically issues CRLs
      and CKLs for its domain.

   $ policy management authority (PMA)
      (I) /PKI/ A person, role, or organization within a PKI that is
      responsible for (a) creating or approving the content of the
      certificate policies and CPSs that are used in the PKI; (b)
      ensuring the administration of those policies; and (c) approving
      any cross-certification or interoperability agreements with CAs
      external to the PKI and any related policy mappings. The PMA may
      also be the accreditor for the PKI as a whole or for some of its

      components or applications. [DoD9, PAG] (See: policy approving
      authority.)

      Example: In the U.S. Department of Defense, an organization called
      the Policy Management Authority is responsible for DoD PKI [DoD9].

   $ policy mapping
      (I) "Recognizing that, when a CA in one domain certifies a CA in
      another domain, a particular certificate policy in the second
      domain may be considered by the authority of the first domain to
      be equivalent (but not necessarily identical in all respects) to a
      particular certificate policy in the first domain." [X509]

   $ policy rule
      (I) A building block of a security policy; it (a) defines a set of
      system conditions and (b) specifies a set of system actions that
      are to be performed if those conditions occur. [R3198]

   $ POP3
      (I) See: Post Office Protocol, version 3.

   $ POP3 APOP
      (I) A POP3 command (better described as a transaction type, or
      subprotocol) by which a POP3 client optionally uses a keyed hash
      (based on MD5) to authenticate itself to a POP3 server and,
      depending on the server implementation, to protect against replay
      attacks. (See: CRAM, POP3 AUTH, IMAP4 AUTHENTICATE.)

      Tutorial: The server includes a unique time stamp in its greeting
      to the client. The subsequent APOP command sent by the client to
      the server contains the client's name and the hash result of
      applying MD5 to a string formed from both the time stamp and a
      shared secret value that is known only to the client and the
      server. APOP was designed to provide an alternative to using
      POP3's USER and PASS (i.e., password) command pair, in which the
      client sends a cleartext password to the server.

   $ POP3 AUTH
      (I) A POP3 command [R1734] (better described as a transaction
      type, or subprotocol) by which a POP3 client optionally proposes a
      mechanism to a POP3 server to authenticate the client to the
      server and provide other security services. (See: POP3 APOP, IMAP4
      AUTHENTICATE.)

      Tutorial: If the server accepts the proposal, the command is
      followed by performing a challenge-response authentication
      protocol and, optionally, negotiating a protection mechanism for

      subsequent POP3 interactions. The security mechanisms used by POP3
      AUTH are those used by IMAP4.

   $ port scan
      (I) A technique that sends client requests to a range of service
      port addresses on a host. (See: probe. Compare: ping sweep.)

      Tutorial: A port scan can be used for pre-attack surveillance,
      with the goal of finding an active port and subsequently
      exploiting a known vulnerability of that port's service. A port
      scan can also be used as a flooding attack.

   $ positive authorization
      (I) The principle that a security architecture should be designed
      so that access to system resources is permitted only when
      explicitly granted; i.e., in the absence of an explicit
      authorization that grants access, the default action shall be to
      refuse access. (See: authorization, access.)

   $ POSIX
      (N) Portable Operating System Interface for Computer Environments,
      a standard [FP151, I9945] (originally IEEE Standard P1003.1) that
      defines an operating system interface and environment to support
      application portability at the source code level. It is intended
      to be used by both application developers and system implementers.

      Tutorial: P1003.1 supports security functionality like that on
      most UNIX systems, including discretionary access control and
      privileges. IEEE Draft Standard P1003.6 specifies additional
      functionality not provided in the base standard, including (a)
      discretionary access control, (b) audit trail mechanisms, (c)
      privilege mechanisms, (d) mandatory access control, and (e)
      information label mechanisms.

   $ Post Office Protocol, version 3 (POP3)
      (I) An Internet Standard protocol (RFC 1939) by which a client
      workstation can dynamically access a mailbox on a server host to
      retrieve mail messages that the server has received and is holding
      for the client. (See: IMAP4.)

      Tutorial: POP3 has mechanisms for optionally authenticating a
      client to a server and providing other security services. (See:
      POP3 APOP, POP3 AUTH.)

   $ PPP
      (I) See: Point-to-Point Protocol.

   $ PPTP
      (I) See: Point-to-Point Tunneling Protocol.

   $ preauthorization
      (N) /PKI/ A CAW feature that enables certification requests to be
      automatically validated against data provided in advance to the CA
      by an authorizing entity.

   $ precedence
      1. (I) /information system/ A ranking assigned to events or data
      objects that determines the relative order in which they are
      processed.

      2. (N) /communication system/ A designation assigned to a
      communication (i.e., packet, message, data stream, connection,
      etc.) by the originator to state the importance or urgency of that
      communication versus other communications, and thus indicate to
      the transmission system the relative order of handling, and
      indicate to the receiver the order in which the communication is
      to be noted. [F1037] (See: availability, critical, preemption.)

      Example: The "Precedence" subfield of the "Type of Service" field
      of the IPv4 header supports the following designations (in
      descending order of importance): 111 Network Control, 110
      Internetwork Control, 101 CRITIC/ECP (Critical Intelligence
      Communication/Emergency Command Precedence), 100 Flash Override,
      011 Flash, 010 Immediate, 001 Priority, and 000 Routine. These
      designations were adopted from U.S. DoD systems that existed
      before ARPANET.

   $ preemption
      (N) The seizure, usually automatic, of system resources that are
      being used to serve a lower-precedence communication, in order to
      serve immediately a higher-precedence communication. [F1037]

   $ Pretty Good Privacy(trademark) (PGP(trademark))
      (O) Trademarks of Network Associates, Inc., referring to a
      computer program (and related protocols) that uses cryptography to
      provide data security for electronic mail and other applications
      on the Internet. (Compare: DKIM, MOSS, MSP, PEM, S/MIME.)

      Tutorial: PGP encrypts messages with a symmetric algorithm
      (originally, IDEA in CFB mode), distributes the symmetric keys by
      encrypting them with an asymmetric algorithm (originally, RSA),
      and creates digital signatures on messages with a cryptographic
      hash and an asymmetric encryption algorithm (originally, MD5 and
      RSA). To establish ownership of public keys, PGP depends on the
      "web of trust".

   $ prevention
      (I) See: secondary definition under "security".

   $ primary account number (PAN)
      (O) /SET/ "The assigned number that identifies the card issuer and
      cardholder. This account number is composed of an issuer
      identification number, an individual account number
      identification, and an accompanying check digit as defined by ISO
      7812-1985." [SET2, I7812] (See: bank identification number.)

      Tutorial: The PAN is embossed, encoded, or both on a magnetic-
      strip-based credit card. The PAN identifies the issuer to which a
      transaction is to be routed and the account to which it is to be
      applied unless specific instructions indicate otherwise. The
      authority that assigns the BIN part of the PAN is the American
      Bankers Association.

   $ principal
      (I) A specific identity claimed by a user when accessing a system.

      Usage: Usually understood to be an identity that is registered in
      and authenticated by the system; equivalent to the notion of login
      account identifier. Each principal is normally assigned to a
      single user, but a single user may be assigned (or attempt to use)
      more than one principal. Each principal can spawn one or more
      subjects, but each subject is associated with only one principal.
      (Compare: role, subject, user.)

      (I) /Kerberos/ A uniquely identified (i.e., uniquely named) client
      or server instance that participates in a network communication.

   $ priority
      (I) /information system/ Precedence for processing an event or
      data object, determined by security importance or other factors.
      (See: precedence.)

   $ privacy
      1. (I) The right of an entity (normally a person), acting in its
      own behalf, to determine the degree to which it will interact with
      its environment, including the degree to which the entity is
      willing to share its personal information with others. (See:
      HIPAA, personal information, Privacy Act of 1974. Compare:
      anonymity, data confidentiality.) [FP041]

      2. (O) "The right of individuals to control or influence what
      information related to them may be collected and stored and by
      whom and to whom that information may be disclosed." [I7498-2]

      3. (D) Synonym for "data confidentiality".

      Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
      for "data confidentiality" or "data confidentiality service",
      which are different concepts. Privacy is a reason for security
      rather than a kind of security. For example, a system that stores
      personal data needs to protect the data to prevent harm,
      embarrassment, inconvenience, or unfairness to any person about
      whom data is maintained, and to protect the person's privacy. For
      that reason, the system may need to provide data confidentiality
      service.

      Tutorial: The term "privacy" is used for various separate but
      related concepts, including bodily privacy, territorial privacy,
      personal information privacy, and communication privacy. IDOCs are
      expected to address only communication privacy, which in this
      Glossary is defined primarily by "data confidentiality" and
      secondarily by "data integrity".

      IDOCs are not expected to address information privacy, but this
      Glossary provides definition 1 for that concept because personal
      information privacy is often confused with communication privacy.
      IDOCs are not expected to address bodily privacy or territorial
      privacy, and this Glossary does not define those concepts because
      they are not easily confused with communication privacy.

   $ Privacy Act of 1974
      (O) A U.S. Federal law (Section 552a of Title 5, United States
      Code) that seeks to balance the U.S. Government's need to maintain
      data about individuals with the rights of individuals to be
      protected against unwarranted invasions of their privacy stemming
      from federal agencies' collection, maintenance, use, and
      disclosure of personal data. (See: privacy.)

      Tutorial: In 1974, the U.S. Congress was concerned with the
      potential for abuses that could arise from the Government's
      increasing use of computers to store and retrieve personal data.
      Therefore, the Act has four basic policy objectives:
      -  To restrict disclosure of personally identifiable records
         maintained by Federal agencies.
      -  To grant individuals increased rights of access to Federal
         agency records maintained on themselves.
      -  To grant individuals the right to seek amendment of agency
         records maintained on themselves upon a showing that the
         records are not accurate, relevant, timely, or complete.
      -  To establish a code of "fair information practices" that
         requires agencies to comply with statutory norms for
         collection, maintenance, and dissemination of records.

   $ Privacy Enhanced Mail (PEM)
      (I) An Internet protocol to provide data confidentiality, data
      integrity, and data origin authentication for electronic mail.
      [R1421, R1422]. (Compare: DKIM, MOSS, MSP, PGP, S/MIME.)

      Tutorial: PEM encrypts messages with a symmetric algorithm
      (originally, DES in CBC mode), provides distribution for the
      symmetric keys by encrypting them with an asymmetric algorithm
      (originally, RSA), and signs messages with an asymmetric
      encryption algorithm over a cryptographic hash (originally, RSA
      over either MD2 or MD5). To establish ownership of public keys,
      PEM uses a certification hierarchy, with X.509 public-key
      certificates and X.509 CRLs that are signed with an asymmetric
      encryption algorithm over a cryptographic hash (originally, RSA
      over MD2).

      PEM is designed to be compatible with a wide range of key
      management methods, but is limited to specifying security services
      only for text messages and, like MOSS, has not been widely
      implemented in the Internet.

   $ private component
      (I) Synonym for "private key".

      Deprecated Usage: In most cases, IDOCs SHOULD NOT use this term;
      instead, to avoid confusing readers, use "private key". However,
      the term MAY be used when discussing a key pair; e.g., "A key pair
      has a public component and a private component."

   $ private extension
      (I) See: secondary definition under "extension".

   $ private key
      1. (I) The secret component of a pair of cryptographic keys used
      for asymmetric cryptography. (See: key pair, public key, secret
      key.)

      2. (O) In a public key cryptosystem, "that key of a user's key
      pair which is known only by that user." [X509]

   $ Private Line Interface (PLI)
      (I) The first end-to-end packet encryption system for a computer
      network, developed by BBN starting in 1975 for the U.S. DoD,
      incorporating U.S. Government-furnished, military-grade COMSEC
      equipment (TSEC/KG-34). [B1822] (Compare: IPLI.)

   $ privilege
      1a. (I) /access control/ A synonym for "authorization". (See
      authorization. Compare: permission.)

      1b. (I) /computer platform/ An authorization to perform a
      security-relevant function in the context of a computer's
      operating system.

   $ privilege management infrastructure
      (O) "The infrastructure able to support the management of
      privileges in support of a comprehensive authorization service and
      in relationship with a" PKI; i.e., processes concerned with
      attribute certificates. [X509]

      Deprecated Usage: IDOCs SHOULD NOT use this term with this
      definition. This definition is vague, and there is no consensus on
      a more specific one.

   $ privileged process
      (I) A computer process that is authorized (and, therefore,
      trusted) to perform some security-relevant functions that ordinary
      processes are not. (See: privilege, trusted process.)

   $ privileged user
      (I) An user that has access to system control, monitoring, or
      administration functions. (See: privilege, /UNIX/ under "root",
      superuser, user.)

      Tutorial: Privileged users include the following types:
      -  Users with near or complete control of a system, who are
         authorized to set up and administer user accounts, identifiers,
         and authentication information, or are authorized to assign or
         change other users' access to system resources.
      -  Users that are authorized to change control parameters (e.g.,
         network addresses, routing tables, processing priorities) on
         routers, multiplexers, and other important equipment.
      -  Users that are authorized to monitor or perform troubleshooting
         for a system's security functions, typically using special
         tools and features that are not available to ordinary users.

   $ probe
      (I) /verb/ A technique that attempts to access a system to learn
      something about the system. (See: port scan.)

      Tutorial: The purpose of a probe may be offensive, e.g., an
      attempt to gather information for circumventing the system's
      protections; or the purpose may be defensive, e.g., to verify that
      the system is working properly.

   $ procedural security
      (D) Synonym for "administrative security".

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      "administrative security". The term may be misleading because any
      type of security may involve procedures, and procedures may be
      either external to the system or internal. Instead, use
      "administrative security", "communication security", "computer
      security", "emanations security", "personnel security", "physical
      security", or whatever specific type is meant. (See: security
      architecture.)

   $ profile
      See: certificate profile, protection profile.

   $ proof-of-possession protocol
      (I) A protocol whereby a system entity proves to another that it
      possesses and controls a cryptographic key or other secret
      information. (See: zero-knowledge proof.)

   $ proprietary
      (I) Refers to information (or other property) that is owned by an
      individual or organization and for which the use is restricted by
      that entity.

   $ protected checksum
      (I) A checksum that is computed for a data object by means that
      protect against active attacks that would attempt to change the
      checksum to make it match changes made to the data object. (See:
      digital signature, keyed hash, Tutorial under "checksum".)

   $ protective packaging
      (N) "Packaging techniques for COMSEC material that discourage
      penetration, reveal a penetration has occurred or was attempted,
      or inhibit viewing or copying of keying material prior to the time
      it is exposed for use." [C4009] (See: tamper-evident, tamper-
      resistant. Compare: QUADRANT.)

   $ protection authority
      (I) See: secondary definition under "Internet Protocol Security
      Option".

   $ protection level
      (N) /U.S. Government/ An indication of the trust that is needed in
      a system's technical ability to enforce security policy for
      confidentiality. (Compare: /system operation/ under "mode of
      operation".)

      Tutorial: An organization's security policy could define
      protection levels that are based on comparing (a) the sensitivity
      of information handled by a system to (b) the authorizations of
      users that receive information from the system without manual
      intervention and reliable human review. For each level, the policy
      could specify security features and assurances that must be
      included in any system that was intended to operate at that level.

      Example: Given some set of data objects that are classified at one
      or more hierarchical levels and in one or more non-hierarchical
      categories, the following table defines five protection levels for
      systems that would handle that data. Beginning with PL1 and
      evolving to PL5, each successive level would require stronger
      features and assurances to handle the dataset. (See: clearance,
      formal access approval, and need-to-know.)

             Lowest Clearance      Formal Access       Need-To-Know
              Among All Users    Approval of Users      of Users
           +-------------------+-------------------+-------------------+
      PL5  | Some user has no  | [Does not matter.]| [Does not matter.]|
      High | clearance at all. |                   |                   |
           +-------------------+-------------------+-------------------+
      PL4  | All are cleared   | [Does not matter.]| [Does not matter.]|
           | for some data.    |                   |                   |
           +-------------------+-------------------+-------------------+
      PL3  | All are cleared   | Some not approved | [Does not matter.]|
           | for all data.     | for all data.     |                   |
           +-------------------+-------------------+-------------------+
      PL2  | All are cleared   | All are approved  | Some don't need to|
           | for all data.     | for all data.     | to know all data. |
           +-------------------+-------------------+-------------------+
      PL1  | All are cleared   | All are approved  | All have a need   |
      Low  | for all data.     | for all data.     | to know all data. |
           +-------------------+-------------------+-------------------+

   Each of these protection levels can be viewed as being equivalent to
   one or more modes of system operation defined in this Glossary:
   -  PL5 is equivalent to multilevel security mode.
   -  PL4 is equivalent to either multilevel or compartmented
      security mode, depending on the details of users' clearances.
   -  PL3 is equivalent to partitioned security mode.
   -  PL2 is equivalent to system-high security mode.
   -  PL1 is equivalent to dedicated security mode.

   $ protection profile
      (N) /Common Criteria/ An implementation-independent set of
      security requirements for a category of targets of evaluation that

      meet specific consumer needs. [CCIB] Example: [IDSAN]. (See:
      target of evaluation. Compare: certificate profile, package.)

      Tutorial: A protection profile (PP) is the kind of document used
      by consumers to specify functional requirements they want in a
      product, and a security target (ST) is the kind of document used
      by vendors to make functional claims about a product.

      A PP is intended to be a reusable statement of product security
      needs, which are known to be useful and effective, for a set of
      information technology security products that could be built. A PP
      contains a set of security requirements, preferably taken from the
      catalogs in Parts 2 and 3 of the Common Criteria, and should
      include an EAL. A PP could be developed by user communities,
      product developers, or any other parties interested in defining a
      common set of requirements.

   $ protection ring
      (I) One of a hierarchy of privileged operation modes of a system
      that gives certain access rights to processes authorized to
      operate in that mode. (See: Multics.)

   $ protective distribution system (PDS)
      (N) A wireline or fiber-optic communication system used to
      transmit cleartext classified information through an area of
      lesser classification or control. [N7003]

   $ protocol
      1a. (I) A set of rules (i.e., formats and procedures) to implement
      and control some type of association (e.g., communication) between
      systems. Example: Internet Protocol.

      1b. (I) A series of ordered computing and communication steps that
      are performed by two or more system entities to achieve a joint
      objective. [A9042]

   $ protocol control information (PCI)
      (N) See: secondary definition under "protocol data unit".

   $ protocol data unit (PDU)
      (N) A data packet that is defined for peer-to-peer transfers in a
      protocol layer.

      Tutorial: A PDU consists of two disjoint subsets of data: the SDU
      and the PCI. (Although these terms -- PDU, SDU, and PCI --
      originated in the OSIRM, they are also useful and permissible in
      an IPS context.)

      -  The "service data unit" (SDU) in a packet is data that the
         protocol transfers between peer protocol entities on behalf of
         the users of that layer's services. For Layers 1 through 6, the
         layer's users are peer protocol entities at a higher layer; for
         Layer 7, the users are application entities outside the scope
         of the OSIRM.
      -  The "protocol control information" (PCI) in a packet is data
         that peer protocol entities exchange between themselves to
         control their joint operation of the layer.

   $ protocol suite
      (I) A complementary collection of communication protocols used in
      a computer network. (See: IPS, OSI.)

   $ proxy
      1. (I) A computer process that acts on behalf of a user or client.

      2. (I) A computer process -- often used as, or as part of, a
      firewall -- that relays application transactions or a protocol
      between client and server computer systems, by appearing to the
      client to be the server and appearing to the server to be the
      client. (See: SOCKS.)

      Tutorial: In a firewall, a proxy server usually runs on a bastion
      host, which may support proxies for several applications and
      protocols (e.g., FTP, HTTP, and TELNET). Instead of a client in
      the protected enclave connecting directly to an external server,
      the internal client connects to the proxy server, which in turn
      connects to the external server. The proxy server waits for a
      request from inside the firewall, forwards the request to the
      server outside the firewall, gets the response, then sends the
      response back to the client. The proxy may be transparent to the
      clients, or they may need to connect first to the proxy server,
      and then use that association to also initiate a connection to the
      real server.

      Proxies are generally preferred over SOCKS for their ability to
      perform caching, high-level logging, and access control. A proxy
      can provide security service beyond that which is normally part of
      the relayed protocol, such as access control based on peer entity
      authentication of clients, or peer entity authentication of
      servers when clients do not have that ability. A proxy at OSIRM
      Layer 7 can also provide finer-grained security service than can a
      filtering router at Layer 3. For example, an FTP proxy could
      permit transfers out of, but not into, a protected network.

   $ proxy certificate
      (I) An X.509 public-key certificate derived from an end-entity
      certificate, or from another proxy certificate, for the purpose of
      establishing proxies and delegating authorizations in the context
      of a PKI-based authentication system. [R3820]

      Tutorial: A proxy certificate has the following properties:
      -  It contains a critical extension that (a) identifies it as a
         proxy certificate and (b) may contain a certification path
         length constraint and policy constraints.
      -  It contains the public component of a key pair that is distinct
         from that associated with any other certificate.
      -  It is signed by the private component of a key pair that is
         associated with an end-entity certificate or another proxy
         certificate.
      -  Its associated private key can be used to sign only other proxy
         certificates (not end-entity certificates).
      -  Its "subject" DN is derived from its "issuer" DN and is unique.
      -  Its "issuer" DN is the "subject" DN of an end-entity
         certificate or another proxy certificate.

   $ pseudorandom
      (I) A sequence of values that appears to be random (i.e.,
      unpredictable) but is actually generated by a deterministic
      algorithm. (See: compression, random, random number generator.)

   $ pseudorandom number generator
      (I) See: secondary definition under "random number generator".

   $ public component
      (I) Synonym for "public key".

      Deprecated Usage: In most cases, IDOCs SHOULD NOT use this term;
      to avoid confusing readers, use "private key" instead. However,
      the term MAY be used when discussing a key pair; e.g., "A key pair
      has a public component and a private component."

   $ public key
      1. (I) The publicly disclosable component of a pair of
      cryptographic keys used for asymmetric cryptography. (See: key
      pair. Compare: private key.)

      2. (O) In a public key cryptosystem, "that key of a user's key
      pair which is publicly known." [X509]

   $ public-key certificate
      1. (I) A digital certificate that binds a system entity's
      identifier to a public key value, and possibly to additional,
      secondary data items; i.e., a digitally signed data structure that
      attests to the ownership of a public key. (See: X.509 public-key
      certificate.)

      2. (O) "The public key of a user, together with some other
      information, rendered unforgeable by encipherment with the private
      key of the certification authority which issued it." [X509]

      Tutorial: The digital signature on a public-key certificate is
      unforgeable. Thus, the certificate can be published, such as by
      posting it in a directory, without the directory having to protect
      the certificate's data integrity.

   $ public-key cryptography
      (I) Synonym for "asymmetric cryptography".

   $ Public-Key Cryptography Standards (PKCS)
      (N) A series of specifications published by RSA Laboratories for
      data structures and algorithms used in basic applications of
      asymmetric cryptography. [PKCS] (See: PKCS #5 through PKCS #11.)

      Tutorial: The PKCS were begun in 1991 in cooperation with industry
      and academia, originally including Apple, Digital, Lotus,
      Microsoft, Northern Telecom, Sun, and MIT. Today, the
      specifications are widely used, but they are not sanctioned by an
      official standards organization, such as ANSI, ITU-T, or IETF. RSA
      Laboratories retains sole decision-making authority over the PKCS.

   $ public-key forward secrecy (PFS)
      (I) For a key-agreement protocol based on asymmetric cryptography,
      the property that ensures that a session key derived from a set of
      long-term public and private keys will not be compromised if one
      of the private keys is compromised in the future. (See: Usage note
      and other discussion under "perfect forward secrecy".)

   $ public-key Kerberos
      (I) See: Tutorial under "Kerberos", PKINIT.

   $ public-key infrastructure (PKI)
      1. (I) A system of CAs (and, optionally, RAs and other supporting
      servers and agents) that perform some set of certificate
      management, archive management, key management, and token
      management functions for a community of users in an application of
      asymmetric cryptography. (See: hierarchical PKI, mesh PKI,
      security management infrastructure, trust-file PKI.)

      2. (I) /PKIX/ The set of hardware, software, people, policies, and
      procedures needed to create, manage, store, distribute, and revoke
      digital certificates based on asymmetric cryptography.

      Tutorial: The core PKI functions are (a) to register users and
      issue their public-key certificates, (b) to revoke certificates
      when required, and (c) to archive data needed to validate
      certificates at a much later time. Key pairs for data
      confidentiality may be generated (and perhaps escrowed) by CAs or
      RAs, but requiring a PKI client to generate its own digital
      signature key pair helps maintain system integrity of the
      cryptographic system, because then only the client ever possesses
      the private key it uses. Also, an authority may be established to
      approve or coordinate CPSs, which are security policies under
      which components of a PKI operate.

      A number of other servers and agents may support the core PKI, and
      PKI clients may obtain services from them, such as certificate
      validation services. The full range of such services is not yet
      fully understood and is evolving, but supporting roles may include
      archive agent, certified delivery agent, confirmation agent,
      digital notary, directory, key escrow agent, key generation agent,
      naming agent who ensures that issuers and subjects have unique
      identifiers within the PKI, repository, ticket-granting agent,
      time-stamp agent, and validation agent.

   $ purge
      1. (I) Synonym for "erase".

      2. (O) /U.S. Government/ Use degaussing or other methods to render
      magnetically stored data unusable and irrecoverable by any means,
      including laboratory methods. [C4009] (Compare: /U.S. Government/
      erase.)

   $ QUADRANT
      (O) /U.S. Government/ Short name for technology and methods that
      protect cryptographic equipment by making the equipment tamper-
      resistant. [C4009] (Compare: protective packaging, TEMPEST.)

      Tutorial: Equipment cannot be made completely tamper-proof, but it
      can be made tamper-resistant or tamper-evident.

   $ qualified certificate
      (I) A public-key certificate that has the primary purpose of
      identifying a person with a high level of assurance, where the
      certificate meets some qualification requirements defined by an
      applicable legal framework, such as the European Directive on
      Electronic Signature. [R3739]

   $ quick mode
      (I) See: /IKE/ under "mode".

   $ RA
      (I) See: registration authority.

   $ RA domains
      (I) A feature of a CAW that allows a CA to divide the
      responsibility for certificate requests among multiple RAs.

      Tutorial: This ability might be used to restrict access to private
      authorization data that is provided with a certificate request,
      and to distribute the responsibility to review and approve
      certificate requests in high-volume environments. RA domains might
      segregate certificate requests according to an attribute of the
      certificate's subject, such as an organizational unit.

   $ RADIUS
      (I) See: Remote Authentication Dial-In User Service.

   $ Rainbow Series
      (O) /COMPUSEC/ A set of more than 30 technical and policy
      documents with colored covers, issued by the NCSC, that discuss in
      detail the TCSEC and provide guidance for meeting and applying the
      criteria. (See: Green Book, Orange Book, Red Book, Yellow Book.)

   $ random
      (I) In essence, "random" means "unpredictable". [SP22, Knut,
      R4086] (See: cryptographic key, pseudorandom.)
      -  "Random sequence": A sequence in which each successive value is
         obtained merely by chance and does not depend on the preceding
         values of the sequence. In a random sequence of bits, each bit
         is unpredictable; i.e., (a) the probability of each bit being a
         "0" or "1" is 1/2, and (b) the value of each bit is independent
         of any other bit in the sequence.
      -  "Random value": An individual value that is unpredictable;
         i.e., each value in the total population of possibilities has
         equal probability of being selected.

   $ random number generator
      (I) A process that is invoked to generate a random sequence of
      values (usually a sequence of bits) or an individual random value.

      Tutorial: There are two basic types of generators. [SP22]
      -  "(True) random number generator": It uses one or more non-
         deterministic bit sources (e.g., electrical circuit noise,
         timing of human processes such as key strokes or mouse
         movements, semiconductor quantum effects, and other physical

         phenomena) and a processing function that formats the bits, and
         it outputs a sequence of values that is unpredictable and
         uniformly distributed.
      -  "Pseudorandom number generator": It uses a deterministic
         computational process (usually implemented by software) that
         has one or more inputs called "seeds", and it outputs a
         sequence of values that appears to be random according to
         specified statistical tests.

   $ RBAC
      (N) See: role-based access control, rule-based access control.

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the abbreviation is ambiguous.

   $ RC2, RC4, RC6
      (N) See: Rivest Cipher #2, #4, #6.

   $ read
      (I) /security model/ A system operation that causes a flow of
      information from an object to a subject. (See: access mode.
      Compare: write.)

   $ realm
      (I) /Kerberos/ A domain consisting of a set of Kerberized clients,
      Kerberized application servers, and one or more Kerberos
      authentication servers and ticket-granting servers that support
      the clients and applications, all operating under the same
      security policy. (See: domain.)

   $ recovery
      1. (I) /cryptography/ The process of learning or obtaining
      cryptographic data or plain text through cryptanalysis. (See: key
      recovery, data recovery.)

      2a. (I) /system integrity/ The process of restoring a secure state
      in a system after there has been an accidental failure or a
      successful attack. (See: secondary definition under "security",
      system integrity.)

      2b. (I) /system integrity/ The process of restoring an information
      system's assets and operation following damage or destruction.
      (See: contingency plan.)

   $ RED
      1. (N) Designation for data that consists only of clear text, and
      for information system equipment items and facilities that handle

      clear text. Example: "RED key". (See: BCR, color change, RED/BLACK
      separation. Compare: BLACK.)

      Derivation: From the practice of marking equipment with colors to
      prevent operational errors.

      2. (O) /U.S. Government/ Designation applied to information
      systems, and to associated areas, circuits, components, and
      equipment, "in which unencrypted national security information is
      being processed." [C4009]

   $ RED/BLACK separation
      (N) An architectural concept for cryptographic systems that
      strictly separates the parts of a system that handle plain text
      (i.e., RED information) from the parts that handle cipher text
      (i.e., BLACK information). (See: BLACK, RED.)

   $ Red Book
      (D) /slang/ Synonym for "Trusted Network Interpretation of the
      Trusted Computer System Evaluation Criteria" [NCS05].

      Deprecated Term: IDOCs SHOULD NOT use this term. Instead, use the
      full proper name of the document or, in subsequent references, a
      more conventional abbreviation, e.g., TNI-TCSEC. (See: TCSEC,
      Rainbow Series, Deprecated Usage under "Green Book".)

   $ RED key
      (N) A cleartext key, which is usable in its present form (i.e., it
      does not need to be decrypted before being used). (See: RED.
      Compare: BLACK key.)

   $ reference monitor
      (I) "An access control concept that refers to an abstract machine
      that mediates all accesses to objects by subjects." [NCS04] (See:
      security kernel.)

      Tutorial: This concept was described in the Anderson report. A
      reference monitor should be (a) complete (i.e., it mediates every
      access), (b) isolated (i.e., it cannot be modified by other system
      entities), and (c) verifiable (i.e., small enough to be subjected
      to analysis and tests to ensure that it is correct).

   $ reflection attack
      (I) An attack in which a valid data transmission is replayed to
      the originator by an attacker who intercepts the original
      transmission. (Compare: indirect attack, replay attack.)

   $ reflector attack
      (D) Synonym for "indirect attack".

      Deprecated Term: IDOCs SHOULD NOT use this term; it could be
      confused with "reflection attack", which is a different concept.

   $ registered user
      (I) A system entity that is authorized to receive a system's
      products and services or otherwise access system resources. (See:
      registration, user.)

   $ registration
      1. (I) /information system/ A system process that (a) initializes
      an identity (of a system entity) in the system, (b) establishes an
      identifier for that identity, (c) may associate authentication
      information with that identifier, and (d) may issue an identifier
      credential (depending on the type of authentication mechanism
      being used). (See: authentication information, credential,
      identifier, identity, identity proofing.)

      2. (I) /PKI/ An administrative act or process whereby an entity's
      name and other attributes are established for the first time at a
      CA, prior to the CA issuing a digital certificate that has the
      entity's name as the subject. (See: registration authority.)

      Tutorial: Registration may be accomplished either directly, by the
      CA, or indirectly, by a separate RA. An entity is presented to the
      CA or RA, and the authority either records the name(s) claimed for
      the entity or assigns the entity's name(s). The authority also
      determines and records other attributes of the entity that are to
      be bound in a certificate (such as a public key or authorizations)
      or maintained in the authority's database (such as street address
      and telephone number). The authority is responsible, possibly
      assisted by an RA, for verifying the entity's identity and vetting
      the other attributes, in accordance with the CA's CPS.

      Among the registration issues that a CPS may address are the
      following [R3647]:
      -  How a claimed identity and other attributes are verified.
      -  How organization affiliation or representation is verified.
      -  What forms of names are permitted, such as X.500 DN, domain
         name, or IP address.
      -  Whether names are required to be meaningful or unique, and
         within what domain.
      -  How naming disputes are resolved, including the role of
         trademarks.
      -  Whether certificates are issued to entities that are not
         persons.

      -  Whether a person is required to appear before the CA or RA, or
         can instead be represented by an agent.
      -  Whether and how an entity proves possession of the private key
         matching a public key.

   $ registration authority (RA)
      1. (I) An optional PKI entity (separate from the CAs) that does
      not sign either digital certificates or CRLs but has
      responsibility for recording or verifying some or all of the
      information (particularly the identities of subjects) needed by a
      CA to issue certificates and CRLs and to perform other certificate
      management functions. (See: ORA, registration.)

      2. (I) /PKIX/ An optional PKI component, separate from the CA(s).
      The functions that the RA performs will vary from case to case but
      may include identity authentication and name assignment, key
      generation and archiving of key pairs, token distribution, and
      revocation reporting. [R4210]

      Tutorial: Sometimes, a CA may perform all certificate management
      functions for all end users for which the CA signs certificates.
      Other times, such as in a large or geographically dispersed
      community, it may be necessary or desirable to offload secondary
      CA functions and delegate them to an assistant, while the CA
      retains the primary functions (signing certificates and CRLs). The
      tasks that are delegated to an RA by a CA may include personal
      authentication, name assignment, token distribution, revocation
      reporting, key generation, and archiving.

      An RA is an optional PKI entity, separate from the CA, that is
      assigned secondary functions. The duties assigned to RAs vary from
      case to case but may include the following:
      -  Verifying a subject's identity, i.e., performing personal
         authentication functions.
      -  Assigning a name to a subject. (See: distinguished name.)
      -  Verifying that a subject is entitled to have the attributes
         requested for a certificate.
      -  Verifying that a subject possesses the private key that matches
         the public key requested for a certificate.
      -  Performing functions beyond mere registration, such as
         generating key pairs, distributing tokens, handling revocation
         reports, and archiving data. (Such functions may be assigned to
         a PKI component that is separate from both the CA and the RA.)

      3. (O) /SET/ "An independent third-party organization that
      processes payment card applications for multiple payment card
      brands and forwards applications to the appropriate financial
      institutions." [SET2]

   $ regrade
      (I) Deliberately change the security level (especially the
      hierarchical classification level) of information in an authorized
      manner. (See: downgrade, upgrade.)

   $ rekey
      (I) Change the value of a cryptographic key that is being used in
      an application of a cryptographic system. (See: certificate
      rekey.)

      Tutorial: Rekey is required at the end of a cryptoperiod or key
      lifetime.

   $ reliability
      (I) The ability of a system to perform a required function under
      stated conditions for a specified period of time. (Compare:
      availability, survivability.)

   $ reliable human review
      (I) Any manual, automated, or hybrid process or procedure that
      ensures that a human examines a digital object, such as text or an
      image, to determine whether the object may be permitted, according
      to some security policy, to be transferred across a controlled
      interface. (See: guard.)

   $ relying party
      (I) Synonym for "certificate user".

      Usage: Used in a legal context to mean a recipient of a
      certificate who acts in reliance on that certificate. (See: ABA
      Guidelines.)

   $ remanence
      (I) Residual information that can be recovered from a storage
      medium after clearing. (See: clear, magnetic remanence, purge.)

   $ Remote Authentication Dial-In User Service (RADIUS)
      (I) An Internet protocol [R2865] for carrying dial-in users'
      authentication information and configuration information between a
      shared, centralized authentication server (the RADIUS server) and
      a network access server (the RADIUS client) that needs to
      authenticate the users of its network access ports. (See: TACACS.)

      User presents authentication and possibly other information to the
      RADIUS client (e.g., health information regarding the user
      device).

      Tutorial: A user presents authentication information and possibly
      other information to the RADIUS client, and the client passes that
      information to the RADIUS server. The server authenticates the
      client using a shared secret value and checks the presented
      information, and then returns to the client all authorization and
      configuration information needed by the client to serve the user.

   $ renew
      See: certificate renewal.

   $ reordering
      (I) /packet/ See: secondary definition under "stream integrity
      service".

   $ replay attack
      (I) An attack in which a valid data transmission is maliciously or
      fraudulently repeated, either by the originator or by a third
      party who intercepts the data and retransmits it, possibly as part
      of a masquerade attack. (See: active wiretapping, fresh, liveness,
      nonce. Compare: indirect attack, reflection attack.)

   $ repository
      1. (I) A system for storing and distributing digital certificates
      and related information (including CRLs, CPSs, and certificate
      policies) to certificate users. (Compare: archive, directory.)

      2. (O) "A trustworthy system for storing and retrieving
      certificates or other information relevant to certificates." [DSG]

      Tutorial: A certificate is published to those who might need it by
      putting it in a repository. The repository usually is a publicly
      accessible, on-line server. In the FPKI, for example, the expected
      repository is a directory that uses LDAP, but also may be an X.500
      Directory that uses DAP, or an HTTP server, or an FTP server that
      permits anonymous login.

   $ repudiation
      1. (I) Denial by a system entity that was involved in an
      association (especially a communication association that transfers
      data) of having participated in the relationship. (See:
      accountability, non-repudiation service.)

      2. (I) A type of threat action whereby an entity deceives another
      by falsely denying responsibility for an act. (See: deception.)

      Usage: This type of threat action includes the following subtypes:
      -  False denial of origin: Action whereby an originator denies
         responsibility for sending data.
      -  False denial of receipt: Action whereby a recipient denies
         receiving and possessing data.

      3. (O) /OSIRM/ "Denial by one of the entities involved in a
      communication of having participated in all or part of the
      communication." [I7498-2]

   $ Request for Comment (RFC)
      1. (I) One of the documents in the archival series that is the
      official channel for IDOCs and other publications of the Internet
      Engineering Steering Group, the Internet Architecture Board, and
      the Internet community in general. (RFC 2026, 2223) (See: Internet
      Standard.)

      2. (D) A popularly misused synonym for a document on the Internet
      Standards Track, i.e., an Internet Standard, Draft Standard, or
      Proposed Standard. (See: Internet Standard.)

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 2 because many other types of documents also are
      published as RFCs.

   $ residual risk
      (I) The portion of an original risk or set of risks that remains
      after countermeasures have been applied. (Compare: acceptable
      risk, risk analysis.)

   $ restore
      See: card restore.

   $ reverse engineering
      (I) /threat action/ See: secondary definition under "intrusion".

   $ revocation
      See: certificate revocation.

   $ revocation date
      (N) /X.509/ In a CRL entry, a date-time field that states when the
      certificate revocation occurred, i.e., when the CA declared the
      digital certificate to be invalid. (See: invalidity date.)

      Tutorial: The revocation date may not resolve some disputes
      because, in the worst case, all signatures made during the
      validity period of the certificate may have to be considered
      invalid. However, it may be desirable to treat a digital signature

      as valid even though the private key used to sign was compromised
      after the signing. If more is known about when the compromise
      actually occurred, a second date-time, an "invalidity date", can
      be included in an extension of the CRL entry.

   $ revocation list
      See: certificate revocation list.

   $ revoke
      (I) See: certificate revocation.

   $ RFC
      (I) See: Request for Comment.

   $ Rijndael
      (N) A symmetric, block cipher that was designed by Joan Daemen and
      Vincent Rijmen as a candidate for the AES, and that won that
      competition. [Daem] (See: Advanced Encryption Standard.)

   $ risk
      1. (I) An expectation of loss expressed as the probability that a
      particular threat will exploit a particular vulnerability with a
      particular harmful result. (See: residual risk.)

      2. (O) /SET/ "The possibility of loss because of one or more
      threats to information (not to be confused with financial or
      business risk)." [SET2]

      Tutorial: There are four basic ways to deal with a risk [SP30]:
      -  "Risk avoidance": Eliminate the risk by either countering the
         threat or removing the vulnerability. (Compare: "avoidance"
         under "security".)
      -  "Risk transference": Shift the risk to another system or
         entity; e.g., buy insurance to compensate for potential loss.
      -  "Risk limitation": Limit the risk by implementing controls that
         minimize resulting loss.
      -  "Risk assumption": Accept the potential for loss and continue
         operating the system.

   $ risk analysis
      (I) An assessment process that systematically (a) identifies
      valuable system resources and threats to those resources, (b)
      quantifies loss exposures (i.e., loss potential) based on
      estimated frequencies and costs of occurrence, and (c)
      (optionally) recommends how to allocate available resources to
      countermeasures so as to minimize total exposure. (See: risk
      management, business-case analysis. Compare: threat analysis.)

      Tutorial: Usually, it is financially and technically infeasible to
      avoid or transfer all risks (see: "first corollary" of "second
      law" under "Courtney's laws"), and some residual risks will
      remain, even after all available countermeasures have been
      deployed (see: "second corollary" of "second law" under
      "Courtney's laws"). Thus, a risk analysis typically lists risks in
      order of cost and criticality, thereby determining where
      countermeasures should be applied first. [FP031, R2196]

      In some contexts, it is infeasible or inadvisable to attempt a
      complete or quantitative risk analysis because needed data, time,
      and expertise are not available. Instead, basic answers to
      questions about threats and risks may be already built into
      institutional security policies. For example, U.S. DoD policies
      for data confidentiality "do not explicitly itemize the range of
      expected threats" but instead "reflect an operational approach ...
      by stating the particular management controls that must be used to
      achieve [confidentiality] ... Thus, they avoid listing threats,
      which would represent a severe risk in itself, and avoid the risk
      of poor security design implicit in taking a fresh approach to
      each new problem". [NRC91]

   $ risk assumption
      (I) See: secondary definition under "risk".

   $ risk avoidance
      (I) See: secondary definition under "risk".

   $ risk limitation
      (I) See: secondary definition under "risk".

   $ risk management
      1. (I) The process of identifying, measuring, and controlling
      (i.e., mitigating) risks in information systems so as to reduce
      the risks to a level commensurate with the value of the assets
      protected. (See: risk analysis.)

      2. (I) The process of controlling uncertain events that may affect
      information system resources.

      3. (O) "The total process of identifying, controlling, and
      mitigating information system-related risks. It includes risk
      assessment; cost-benefit analysis; and the selection,
      implementation, test, and security evaluation of safeguards. This
      overall system security review considers both effectiveness and
      efficiency, including impact on the mission and constraints due to
      policy, regulations, and laws." [SP30]

   $ risk transference
      (I) See: secondary definition under "risk".

   $ Rivest Cipher #2 (RC2)
      (N) A proprietary, variable-key-length block cipher invented by
      Ron Rivest for RSA Data Security, Inc.

   $ Rivest Cipher #4 (RC4)
      (N) A proprietary, variable-key-length stream cipher invented by
      Ron Rivest for RSA Data Security, Inc.

   $ Rivest Cipher #6 (RC6)
      (N) A symmetric, block cipher with 128-bit or longer key length,
      developed by Ron Rivest for RSA Data Security, Inc. as a candidate
      for the AES.

   $ Rivest-Shamir-Adleman (RSA)
      (N) An algorithm for asymmetric cryptography, invented in 1977 by
      Ron Rivest, Adi Shamir, and Leonard Adleman [RSA78].

      Tutorial: RSA uses exponentiation modulo the product of two large
      prime numbers. The difficulty of breaking RSA is believed to be
      equivalent to the difficulty of factoring integers that are the
      product of two large prime numbers of approximately equal size.

      To create an RSA key pair, randomly choose two large prime
      numbers, p and q, and compute the modulus, n = pq. Randomly choose
      a number e, the public exponent, that is less than n and
      relatively prime to (p-1)(q-1). Choose another number d, the
      private exponent, such that ed-1 evenly divides (p-1)(q-1). The
      public key is the set of numbers (n,e), and the private key is the
      set (n,d).

      It is assumed to be difficult to compute the private key (n,d)
      from the public key (n,e). However, if n can be factored into p
      and q, then the private key d can be computed easily. Thus, RSA
      security depends on the assumption that it is computationally
      difficult to factor a number that is the product of two large
      prime numbers. (Of course, p and q are treated as part of the
      private key, or else are destroyed after computing n.)

      For encryption of a message, m, to be sent to Bob, Alice uses
      Bob's public key (n,e) to compute m**e (mod n) = c. She sends c to
      Bob. Bob computes c**d (mod n) = m. Only Bob knows d, so only Bob
      can compute c**d (mod n) to recover m.

      To provide data origin authentication of a message, m, to be sent
      to Bob, Alice computes m**d (mod n) = s, where (d,n) is Alice's

      private key. She sends m and s to Bob. To recover the message that
      only Alice could have sent, Bob computes s**e (mod n) = m, where
      (e,n) is Alice's public key.

      To ensure data integrity in addition to data origin authentication
      requires extra computation steps in which Alice and Bob use a
      cryptographic hash function h (see: digital signature). Alice
      computes the hash value h(m) = v, and then encrypts v with her
      private key to get s. She sends m and s. Bob receives m' and s',
      either of which might have been changed from the m and s that
      Alice sent. To test this, he decrypts s' with Alice's public key
      to get v'. He then computes h(m') = v". If v' equals v", Bob is
      assured that m' is the same m that Alice sent.

   $ robustness
      (N) See: level of robustness.

   $ role
      1. (I) A job function or employment position to which people or
      other system entities may be assigned in a system. (See: role-
      based access control. Compare: duty, billet, principal, user.)

      2. (O) /Common Criteria/ A pre-defined set of rules establishing
      the allowed interactions between a user and the TOE.

   $ role-based access control
      (I) A form of identity-based access control wherein the system
      entities that are identified and controlled are functional
      positions in an organization or process. [Sand] (See:
      authorization, constraint, identity, principal, role.)

      Tutorial: Administrators assign permissions to roles as needed to
      perform functions in the system. Administrators separately assign
      user identities to roles. When a user accesses the system in an
      identity (for which the user has been registered) and initiates a
      session using a role (to which the user has been assigned), then
      the permissions that have been assigned to the role are available
      to be exercised by the user.

      The following diagram shows that role-based access control
      involves five different relationships: (a) administrators assign
      identities to roles, (b) administrators assign permissions to
      roles, (c) administrators assign roles to roles, (d) users select
      identities in sessions, and (e) users select roles in sessions.
      Security policies may define constraints on these assignments and
      selections.

         (c) Permission Inheritance Assignments (i.e., Role Hierarchy)
                               [Constraints]
                                  +=====+
                                  |     |
                   (a) Identity   v     v  (b) Permission
      +----------+  Assignments  +-------+  Assignments  +----------+
      |Identities|<=============>| Roles |<=============>|Permissions|
      +----------+ [Constraints] +-------+ [Constraints] +----------+
           |   |                   ^   ^
           |   |   +-----------+   |   |       +---------------------+
           |   |   | +-------+ |   |   |       |       Legend        |
           |   +====>|Session|=====+   |       |                     |
           |       | +-------+ |       |       |     One-to-One      |
           |       |    ...   |       |       | =================== |
           |       | +-------+ |       |       |                     |
           +========>|Session|=========+       |     One-to-Many     |
      (d) Identity | +-------+ |  (e) Role     | ==================> |
       Selections  |           | Selections    |                     |
      [Constraints]|  Access   |[Constraints]  |    Many-to-Many     |
                   | Sessions  |               | <=================> |
                   +-----------+               +---------------------+

   $ role certificate
      (I) An organizational certificate that is issued to a system
      entity that is a member of the set of users that have identities
      that are assigned to the same role. (See: role-based access
      control.)

   $ root, root CA
      1. (I) /PKI/ A CA that is directly trusted by an end entity. (See:
      trust anchor, trusted CA.)

      2. (I) /hierarchical PKI/ The CA that is the highest level (most
      trusted) CA in a certification hierarchy; i.e., the authority upon
      whose public key all certificate users base their validation of
      certificates, CRLs, certification paths, and other constructs.
      (See: top CA.)

      Tutorial: The root CA in a certification hierarchy issues public-
      key certificates to one or more additional CAs that form the
      second-highest level. Each of these CAs may issue certificates to
      more CAs at the third-highest level, and so on. To initialize
      operation of a hierarchical PKI, the root's initial public key is
      securely distributed to all certificate users in a way that does
      not depend on the PKI's certification relationships, i.e., by an
      out-of-band procedure. The root's public key may be distributed
      simply as a numerical value, but typically is distributed in a
      self-signed certificate in which the root is the subject. The

      root's certificate is signed by the root itself because there is
      no higher authority in a certification hierarchy. The root's
      certificate is then the first certificate in every certification
      path.

      3. (I) /DNS/ The base of the tree structure that defines the name
      space for the Internet DNS. (See: domain name.)

      4. (O) /MISSI/ A name previously used for a MISSI policy creation
      authority, which is not a root as defined above for general usage,
      but is a CA at the second level of the MISSI hierarchy,
      immediately subordinate to a MISSI policy approving authority.

      5. (O) /UNIX/ A user account (a.k.a. "superuser") that has all
      privileges (including all security-related privileges) and thus
      can manage the system and its other user accounts.

   $ root certificate
      1. (I) /PKI/ A certificate for which the subject is a root. (See:
      trust anchor certificate, trusted certificate.)

      2. (I) /hierarchical PKI/ The self-signed public-key certificate
      at the top of a certification hierarchy.

   $ root key
      (I) /PKI/ A public key for which the matching private key is held
      by a root. (See: trust anchor key, trusted key.)

   $ root registry
      (O) /MISSI/ A name previously used for a MISSI PAA.

   $ ROT13
      (I) See: secondary definition under "Caesar cipher".

   $ router
      1a. (I) /IP/ A networked computer that forwards IP packets that
      are not addressed to the computer itself. (Compare: host.)

      1b. (I) /IPS/ A gateway that operates in the IPS Internet Layer to
      connect two or more subnetworks.

      1c. (N) /OSIRM/ A computer that is a gateway between two networks
      at OSIRM Layer 3 and that relays and directs data packets through
      that internetwork. (Compare: bridge, proxy.)

   $ RSA
      (N) See: Rivest-Shamir-Adleman.

   $ rule
      See: policy rule.

   $ rule-based security policy
      (I) "A security policy based on global rules [i.e., policy rules]
      imposed for all users. These rules usually rely on comparison of
      the sensitivity of the resource being accessed and the possession
      of corresponding attributes of users, a group of users, or
      entities acting on behalf of users." [I7498-2] (Compare: identity-
      based security policy, policy rule, RBAC.)

   $ rules of behavior
      (I) A body of security policy that has been established and
      implemented concerning the responsibilities and expected behavior
      of entities that have access to a system. (Compare: [R1281].)

      Tutorial: For persons employed by a corporation or government, the
      rules might cover such matters as working at home, remote access,
      use of the Internet, use of copyrighted works, use of system
      resources for unofficial purpose, assignment and limitation of
      system privileges, and individual accountability.

   $ S field
      (D) See: Security Level field.

   $ S-BGP
      (I) See: Secure BGP.

   $ S-HTTP
      (I) See: Secure Hypertext Transfer Protocol.

   $ S/Key
      (I) A security mechanism that uses a cryptographic hash function
      to generate a sequence of 64-bit, one-time passwords for remote
      user login. [R1760]

      Tutorial: The client generates a one-time password by applying the
      MD4 cryptographic hash function multiple times to the user's
      secret key. For each successive authentication of the user, the
      number of hash applications is reduced by one. (Thus, an intruder
      using wiretapping cannot compute a valid password from knowledge
      of one previously used.) The server verifies a password by hashing
      the currently presented password (or initialization value) one
      time and comparing the hash result with the previously presented
      password.

   $ S/MIME
      (I) See: Secure/MIME.

   $ SAD
      (I) See: Security Association Database.

   $ safety
      (I) The property of a system being free from risk of causing harm
      (especially physical harm) to its system entities. (Compare:
      security.)

   $ SAID
      (I) See: security association identifier.

   $ salami swindle
      (D) /slang/ "Slicing off a small amount from each transaction.
      This kind of theft was made worthwhile by automation. Given a high
      transaction flow, even rounding down to the nearest cent and
      putting the 'extra' in a bogus account can be very profitable."
      [NCSSG]

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ salt
      (I) A data value used to vary the results of a computation in a
      security mechanism, so that an exposed computational result from
      one instance of applying the mechanism cannot be reused by an
      attacker in another instance. (Compare: initialization value.)

      Example: A password-based access control mechanism might protect
      against capture or accidental disclosure of its password file by
      applying a one-way encryption algorithm to passwords before
      storing them in the file. To increase the difficulty of off-line,
      dictionary attacks that match encrypted values of potential
      passwords against a copy of the password file, the mechanism can
      concatenate each password with its own random salt value before
      applying the one-way function.

   $ SAML
      (N) See: Security Assertion Markup Language (SAML).

   $ sandbox
      (I) A restricted, controlled execution environment that prevents
      potentially malicious software, such as mobile code, from
      accessing any system resources except those for which the software
      is authorized.

   $ sanitize
      1. (I) Delete sensitive data from a file, device, or system. (See:
      erase, zeroize.)

      2. (I) Modify data so as to be able either (a) to completely
      declassify it or (b) to downgrade it to a lower security level.

   $ SAP
      (O) See: special access program.

   $ SASL
      (I) See: Simple Authentication and Security Layer.

   $ SCA
      (I) See: subordinate certification authority.

   $ scavenging
      (I) /threat action/ See: secondary definition under "exposure".

   $ SCI
      (O) See: sensitive compartmented information.

   $ SCIF
      (O) See: sensitive compartmented information facility.

   $ SCOMP
      (N) Secure COMmunications Processor; an enhanced, MLS version of
      the Honeywell Level 6 minicomputer. It was the first system to be
      rated in TCSEC Class A1. (See: KSOS.)

   $ screen room
      (D) /slang/ Synonym for "shielded enclosure" in the context of
      electromagnetic emanations. (See: EMSEC, TEMPEST.)

      Deprecated Term: To avoid international misunderstanding, IDOCs
      SHOULD NOT use this term.

   $ screening router
      (I) Synonym for "filtering router".

   $ script kiddy
      (D) /slang/ A cracker who is able to use existing attack
      techniques (i.e., to read scripts) and execute existing attack
      software, but is unable to invent new exploits or manufacture the
      tools to perform them; pejoratively, an immature or novice
      cracker.

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ SDE
      (N) See: Secure Data Exchange.

   $ SDNS
      (O) See: Secure Data Network System.

   $ SDU
      (N) See: "service data unit" under "protocol data unit".

   $ seal
      1. (I) To use asymmetric cryptography to encrypt plain text with a
      public key in such a way that only the holder of the matching
      private key can learn what was the plain text. [Chau] (Compare:
      shroud, wrap.)

      Deprecated Usage: An IDOC SHOULD NOT use this term with definition
      1 unless the IDOC includes the definition, because the definition
      is not widely known and the concept can be expressed by using
      other, standard terms. Instead, use "salt and encrypt" or other
      terminology that is specific with regard to the mechanism being
      used.

      Tutorial: The definition does *not* say "only the holder of the
      matching private key can decrypt the ciphertext to learn what was
      the plaintext"; sealing is stronger than that. If Alice simply
      encrypts a plaintext P with a public key K to produce ciphertext C
      = K(P), then if Bob guesses that P = X, Bob could verify the guess
      by checking whether K(P) = K(X). To "seal" P and block Bob's
      guessing attack, Alice could attach a long string R of random bits
      to P before encrypting to produce C = K(P,R); if Bob guesses that
      P = X, Bob can only test the guess by also guessing R. (See:
      salt.)

      2. (D) To use cryptography to provide data integrity service for a
      data object. (See: sign.)

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 2. Instead, use a term that is more specific with
      regard to the mechanism used to provide the data integrity
      service; e.g., use "sign" when the mechanism is digital signature.

   $ secret
      1a. (I) /adjective/ The condition of information being protected
      from being known by any system entities except those that are
      intended to know it. (See: data confidentiality.)

      1b. (I) /noun/ An item of information that is protected thusly.

      Usage: This term applies to symmetric keys, private keys, and
      passwords.

   $ secret key
      (D) A key that is kept secret or needs to be kept secret.

      Deprecated Term: IDOCs SHOULD NOT use this term; it mixes concepts
      in a potentially misleading way. In the context of asymmetric
      cryptography, IDOCs SHOULD use "private key". In the context of
      symmetric cryptography, the adjective "secret" is unnecessary
      because all keys must be kept secret.

   $ secret-key cryptography
      (D) Synonym for "symmetric cryptography".

      Deprecated Term: IDOCs SHOULD NOT use this term; it could be
      confused with "asymmetric cryptography", in which the private key
      is kept secret.

      Derivation: Symmetric cryptography is sometimes called "secret-key
      cryptography" because entities that share the key, such as the
      originator and the recipient of a message, need to keep the key
      secret from other entities.

   $ Secure BGP (S-BGP)
      (I) A project of BBN Technologies, sponsored by the U.S. DoD's
      Defense Advanced Research Projects Agency, to design and
      demonstrate an architecture to secure the Border Gateway Protocol
      (RFC 1771) and to promote deployment of that architecture in the
      Internet.

      Tutorial: S-BGP incorporates three security mechanisms:
      -  A PKI supports authentication of ownership of IP address
         blocks, autonomous system (AS) numbers, an AS's identity, and a
         BGP router's identity and its authorization to represent an AS.
         This PKI parallels and takes advantage of the Internet's
         existing IP address and AS number assignment system.
      -  A new, optional, BGP transitive path attribute carries digital
         signatures (in "attestations") covering the routing information
         in a BGP UPDATE. These signatures along with certificates from
         the S-BGP PKI enable the receiver of a BGP routing UPDATE to

         validate the attribute and gain trust in the address prefixes
         and path information that it contains.
      -  IPsec provides data and partial sequence integrity, and enables
         BGP routers to authenticate each other for exchanges of BGP
         control traffic.

   $ Secure Data Exchange (SDE)
      (N) A LAN security protocol defined by the IEEE 802.10 standard.

   $ Secure Data Network System (SDNS)
      (O) An NSA program that developed security protocols for
      electronic mail (see: MSP), OSIRM Layer 3 (see: SP3), OSIRM Layer
      4 (see: SP4), and key establishment (see: KMP).

   $ secure distribution
      (I) See: trusted distribution.

   $ Secure Hash Algorithm (SHA)
      (N) A cryptographic hash function (specified in SHS) that produces
      an output (see: "hash result") -- of selectable length of either
      160, 224, 256, 384, or 512 bits -- for input data of any length <
      2**64 bits.

   $ Secure Hash Standard (SHS)
      (N) The U.S. Government standard [FP180] that specifies SHA.

   $ Secure Hypertext Transfer Protocol (S-HTTP)
      (I) An Internet protocol [R2660] for providing client-server
      security services for HTTP communications. (Compare: https.)

      Tutorial: S-HTTP was originally specified by CommerceNet, a
      coalition of businesses interested in developing the Internet for
      commercial uses. Several message formats may be incorporated into
      S-HTTP clients and servers, particularly CMS and MOSS. S-HTTP
      supports choice of security policies, key management mechanisms,
      and cryptographic algorithms through option negotiation between
      parties for each transaction. S-HTTP supports modes of operation
      for both asymmetric and symmetric cryptography. S-HTTP attempts to
      avoid presuming a particular trust model, but it attempts to
      facilitate multiply rooted, hierarchical trust and anticipates
      that principals may have many public-key certificates.

   $ Secure/MIME (S/MIME)
      (I) Secure/Multipurpose Internet Mail Extensions, an Internet
      protocol [R3851] to provide encryption and digital signatures for
      Internet mail messages.

   $ secure multicast
      (I) Refers generally to providing security services for multicast
      groups of various types (e.g., 1-to-N and M-to-N) and to classes
      of protocols used to protect multicast packets.

      Tutorial: Multicast applications include video broadcast and
      multicast file transfer, and many of these applications require
      network security services. The Multicast Security Reference
      Framework [R3740] covers three functional areas:
      -  Multicast data handling: Security-related treatment of
         multicast data by the sender and the receiver.
      -  Group key management: Secure distribution and refreshment of
         keying material. (See: Group Domain of Interpretation.)
      -  Multicast security policy: Policy translation and
         interpretation across the multiple administrative domains that
         typically are spanned by a multicast application.

   $ Secure Shell(trademark) (SSH(trademark))
      (N) Refers to a protocol for secure remote login and other secure
      network services.

      Usage: On the Web site of SSH Communication Security Corporation,
      at http://www.ssh.com/legal_notice.html, it says, "SSH [and] the
      SSH logo ... are either trademarks or registered trademarks of
      SSH." This Glossary seeks to make readers aware of this trademark
      claim but takes no position on its validity.

      Tutorial: SSH has three main parts:
      -  Transport layer protocol: Provides server authentication,
         confidentiality, and integrity; and can optionally provide
         compression. This layer typically runs over a TCP connection,
         but might also run on top of any other reliable data stream.
      -  User authentication protocol: Authenticates the client-side
         user to the server. It runs over the transport layer protocol.
      -  Connection protocol: Multiplexes the encrypted tunnel into
         several logical channels. It runs over the user authentication
         protocol.

   $ Secure Sockets Layer (SSL)
      (N) An Internet protocol (originally developed by Netscape
      Communications, Inc.) that uses connection-oriented end-to-end
      encryption to provide data confidentiality service and data
      integrity service for traffic between a client (often a web
      browser) and a server, and that can optionally provide peer entity
      authentication between the client and the server. (See: Transport
      Layer Security.)

      Tutorial: SSL has two layers; SSL's lower layer, the SSL Record
      Protocol, is layered on top of an IPS Transport-Layer protocol and
      encapsulates protocols that run in the upper layer. The upper-
      layer protocols are the three SSL management protocols -- SSL
      Handshake Protocol, SSL Change Cipher Spec Protocol, or SSL Alert
      Protocol -- and some Application-Layer protocol (e.g., HTTP).

      The SSL management protocols provide asymmetric cryptography for
      server authentication (verifying the server's identity to the
      client) and optional client authentication (verifying the client's
      identity to the server), and also enable them, before the
      application protocol transmits or receives data, to negotiate a
      symmetric encryption algorithm and secret session key (to use for
      data confidentiality service) and a keyed hash (to use for data
      integrity service).

      SSL is independent of the application it encapsulates, and any
      application can layer on top of SSL transparently. However, many
      Internet applications might be better served by IPsec.

   $ secure state
      1a. (I) A system condition in which the system is in conformance
      with the applicable security policy. (Compare: clean system,
      transaction.)

      1b. (I) /formal model/ A system condition in which no subject can
      access any object in an unauthorized manner. (See: secondary
      definition under "Bell-LaPadula model".)

   $ security
      1a. (I) A system condition that results from the establishment and
      maintenance of measures to protect the system.

      1b. (I) A system condition in which system resources are free from
      unauthorized access and from unauthorized or accidental change,
      destruction, or loss. (Compare: safety.)

      2. (I) Measures taken to protect a system.

      Tutorial: Parker [Park] suggests that providing a condition of
      system security may involve the following six basic functions,
      which overlap to some extent:
      -  "Deterrence": Reducing an intelligent threat by discouraging
         action, such as by fear or doubt. (See: attack, threat action.)
      -  "Avoidance": Reducing a risk by either reducing the value of
         the potential loss or reducing the probability that the loss
         will occur. (See: risk analysis. Compare: "risk avoidance"
         under "risk".)

      -  "Prevention": Impeding or thwarting a potential security
         violation by deploying a countermeasure.
      -  "Detection": Determining that a security violation is
         impending, is in progress, or has recently occurred, and thus
         make it possible to reduce the potential loss. (See: intrusion
         detection.)
      -  "Recovery": Restoring a normal state of system operation by
         compensating for a security violation, possibly by eliminating
         or repairing its effects. (See: contingency plan, main entry
         for "recovery".)
      -  "Correction": Changing a security architecture to eliminate or
         reduce the risk of reoccurrence of a security violation or
         threat consequence, such as by eliminating a vulnerability.

   $ security architecture
      (I) A plan and set of principles that describe (a) the security
      services that a system is required to provide to meet the needs of
      its users, (b) the system components required to implement the
      services, and (c) the performance levels required in the
      components to deal with the threat environment (e.g., [R2179]).
      (See: defense in depth, IATF, OSIRM Security Architecture,
      security controls, Tutorial under "security policy".)

      Tutorial: A security architecture is the result of applying the
      system engineering process. A complete system security
      architecture includes administrative security, communication
      security, computer security, emanations security, personnel
      security, and physical security. A complete security architecture
      needs to deal with both intentional, intelligent threats and
      accidental threats.

   $ Security Assertion Markup Language (SAML)
      (N) A protocol consisting of XML-based request and response
      message formats for exchanging security information, expressed in
      the form of assertions about subjects, between on-line business
      partners. [SAML]

   $ security association
      1. (I) A relationship established between two or more entities to
      enable them to protect data they exchange. (See: association,
      ISAKMP, SAD. Compare: session.)

      Tutorial: The relationship is represented by a set of data that is
      shared between the entities and is agreed upon and considered a
      contract between them. The data describes how the associated
      entities jointly use security services. The relationship is used
      to negotiate characteristics of security mechanisms, but the

      relationship is usually understood to exclude the mechanisms
      themselves.

      2. (I) /IPsec/ A simplex (uni-directional) logical connection
      created for security purposes and implemented with either AH or
      ESP (but not both). The security services offered by a security
      association depend on the protocol (AH or ESP), the IPsec mode
      (transport or tunnel), the endpoints, and the election of optional
      services within the protocol. A security association is identified
      by a triple consisting of (a) a destination IP address, (b) a
      protocol (AH or ESP) identifier, and (c) a Security Parameter
      Index.

      3. (O) "A set of policy and cryptographic keys that provide
      security services to network traffic that matches that policy".
      [R3740] (See: cryptographic association, group security
      association.)

      4. (O) "The totality of communications and security mechanisms and
      functions (e.g., communications protocols, security protocols,
      security mechanisms and functions) that securely binds together
      two security contexts in different end systems or relay systems
      supporting the same information domain." [DoD6]

   $ Security Association Database (SAD)
      (I) /IPsec/ In an IPsec implementation that operates in a network
      node, a database that contains parameters to describe the status
      and operation of each of the active security associations that the
      node has established with other nodes. Separate inbound and
      outbound SADs are needed because of the directionality of IPsec
      security associations. [R4301] (Compare: SPD.)

   $ security association identifier (SAID)
      (I) A data field in a security protocol (such as NLSP or SDE),
      used to identify the security association to which a PDU is bound.
      The SAID value is usually used to select a key for decryption or
      authentication at the destination. (See: Security Parameter
      Index.)

   $ security assurance
      1. (I) An attribute of an information system that provides grounds
      for having confidence that the system operates such that the
      system's security policy is enforced. (Compare: trust.)

      2. (I) A procedure that ensures a system is developed and operated
      as intended by the system's security policy.

      3. (D) "The degree of confidence one has that the security
      controls operate correctly and protect the system as intended."
      [SP12]

      Deprecated Definition: IDOCs SHOULD NOT use definition 3; it is a
      definition for "assurance level" rather than for "assurance".

      4. (D) /U.S. Government, identity authentication/ The (a) "degree
      of confidence in the vetting process used to establish the
      identity of the individual to whom the [identity] credential was
      issued" and the (b) "degree of confidence that the individual who
      uses the credential is the individual to whom the credential was
      issued". [M0404]

      Deprecated Definition: IDOCs SHOULD NOT use definition 4; it mixes
      concepts in a potentially misleading way. Part "a" is a definition
      for "assurance level" (rather than "security assurance") of an
      identity registration process; and part "b" is a definition for
      "assurance level" (rather than "security assurance") of an
      identity authentication process. Also, the processes of
      registration and authentication should be defined and designed
      separately to ensure clarity in certification.

   $ security audit
      (I) An independent review and examination of a system's records
      and activities to determine the adequacy of system controls,
      ensure compliance with established security policy and procedures,
      detect breaches in security services, and recommend any changes
      that are indicated for countermeasures. [I7498-2, NCS01] (Compare:
      accounting, intrusion detection.)

      Tutorial: The basic audit objective is to establish accountability
      for system entities that initiate or participate in security-
      relevant events and actions. Thus, means are needed to generate
      and record a security audit trail and to review and analyze the
      audit trail to discover and investigate security violations.

   $ security audit trail
      (I) A chronological record of system activities that is sufficient
      to enable the reconstruction and examination of the sequence of
      environments and activities surrounding or leading to an
      operation, procedure, or event in a security-relevant transaction
      from inception to final results. [NCS04] (See: security audit.)

   $ security by obscurity
      (O) Attempting to maintain or increase security of a system by
      keeping secret the design or construction of a security mechanism.

      Tutorial: This approach has long been discredited in cryptography,
      where the phrase refers to trying to keep an algorithm secret,
      rather than just concealing the keys [Schn]. One must assume that
      mass-produced or widely fielded cryptographic devices eventually
      will be lost or stolen and, therefore, that the algorithms will be
      reverse engineered and become known to the adversary. Thus, one
      should rely on only those algorithms and protocols that are strong
      enough to have been published widely, and have been peer reviewed
      for long enough that their flaws have been found and removed. For
      example, NIST used a long, public process to select AES to replace
      DES.

      In computer and network security, the principle of "no security by
      obscurity" also applies to security mechanisms other than
      cryptography. For example, if the design and implementation of a
      protocol for access control are strong, then reading the
      protocol's source code should not enable you to find a way to
      evade the protection and penetrate the system.

   $ security class
      (D) Synonym for "security level".

      Deprecated Term: IDOCs SHOULD NOT use this term. Instead, use
      "security level", which is more widely established and understood.

   $ security clearance
      (I) A determination that a person is eligible, under the standards
      of a specific security policy, for authorization to access
      sensitive information or other system resources. (See: clearance
      level.)

   $ security compromise
      (I) A security violation in which a system resource is exposed, or
      is potentially exposed, to unauthorized access. (Compare: data
      compromise, exposure, violation.)

   $ security controls
      (N) The management, operational, and technical controls
      (safeguards or countermeasures) prescribed for an information
      system which, taken together, satisfy the specified security
      requirements and adequately protect the confidentiality,
      integrity, and availability of the system and its information.
      [FP199] (See: security architecture.)

   $ security doctrine
      (I) A specified set of procedures or practices that direct or
      provide guidance for how to comply with security policy. (Compare:
      security mechanism, security policy.)

      Tutorial: Security policy and security doctrine are closely
      related. However, policy deals mainly with strategy, and doctrine
      deals with tactics.

      Security doctrine is often understood to refer mainly to
      administrative security, personnel security, and physical
      security. For example, security mechanisms and devices that
      implement them are normally designed to operate in a limited range
      of environmental and administrative conditions, and these
      conditions must be met to complement and ensure the technical
      protection afforded by the hardware, firmware, and software in the
      devices. Security doctrine specifies how to achieve those
      conditions. (See: "first law" under "Courtney's laws".)

   $ security domain
      (I) See: domain.

   $ security environment
      (I) The set of external entities, procedures, and conditions that
      affect secure development, operation, and maintenance of a system.
      (See: "first law" under "Courtney's laws".)

   $ security event
      (I) An occurrence in a system that is relevant to the security of
      the system. (See: security incident.)

      Tutorial: The term covers both events that are security incidents
      and those that are not. In a CA workstation, for example, a list
      of security events might include the following:
      -  Logging an operator into or out of the system.
      -  Performing a cryptographic operation, e.g., signing a digital
         certificate or CRL.
      -  Performing a cryptographic card operation: creation, insertion,
         removal, or backup.
      -  Performing a digital certificate lifecycle operation: rekey,
         renewal, revocation, or update.
      -  Posting a digital certificate to an X.500 Directory.
      -  Receiving a key compromise notification.
      -  Receiving an improper certification request.
      -  Detecting an alarm condition reported by a cryptographic
         module.
      -  Failing a built-in hardware self-test or a software system
         integrity check.

   $ security fault analysis
      (I) A security analysis, usually performed on hardware at the
      level of gate logic, gate-by-gate, to determine the security
      properties of a device when a hardware fault is encountered.

   $ security function
      (I) A function in a system that is relevant to the security of the
      system; i.e., a system function that must operate correctly to
      ensure adherence to the system's security policy.

   $ security gateway
      1. (I) An internetwork gateway that separates trusted (or
      relatively more trusted) hosts on one side from untrusted (or less
      trusted) hosts on the other side. (See: firewall and guard.)

      2. (O) /IPsec/ "An intermediate system that implements IPsec
      protocols." [R4301]

      Tutorial: IPsec's AH or ESP can be implemented on a gateway
      between a protected network and an unprotected network, to provide
      security services to the protected network's hosts when they
      communicate across the unprotected network to other hosts and
      gateways.

   $ security incident
      1. (I) A security event that involves a security violation. (See:
      CERT, security event, security intrusion, security violation.)

      Tutorial: In other words, a security event in which the system's
      security policy is disobeyed or otherwise breached.

      2. (D) "Any adverse event [that] compromises some aspect of
      computer or network security." [R2350]

      Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
      (a) a security incident may occur without actually being harmful
      (i.e., adverse) and because (b) this Glossary defines "compromise"
      more narrowly in relation to unauthorized access.

      3. (D) "A violation or imminent threat of violation of computer
      security policies, acceptable use policies, or standard computer
      security practices." [SP61]

      Deprecated Definition: IDOCs SHOULD NOT use definition 3 because
      it mixes concepts in way that does not agree with common usage; a
      security incident is commonly thought of as involving a
      realization of a threat (see: threat action), not just a threat.

   $ security intrusion
      (I) A security event, or a combination of multiple security
      events, that constitutes a security incident in which an intruder
      gains, or attempts to gain, access to a system or system resource
      without having authorization to do so.

   $ security kernel
      (I) "The hardware, firmware, and software elements of a trusted
      computing base that implement the reference monitor concept. It
      must mediate all accesses, be protected from modification, and be
      verifiable as correct." [NCS04] (See: kernel, TCB.)

      Tutorial: A security kernel is an implementation of a reference
      monitor for a given hardware base. [Huff]

   $ security label
      (I) An item of meta-data that designates the value of one or more
      security-relevant attributes (e.g., security level) of a system
      resource. (See: [R1457]. Compare: security marking.)

      Deprecated usage: To avoid confusion, IDOCs SHOULD NOT use
      "security label" for "security marking", or vice versa, even
      though that is commonly done (including in some national and
      international standards that should know better).

      Tutorial: Humans and automated security mechanisms use a security
      label of a system resource to determine, according to applicable
      security policy, how to control access to the resource (and they
      affix appropriate, matching security markings to physical
      instances of the resource). Security labels are most often used to
      support data confidentiality policy, and sometimes used to support
      data integrity policy.

      As explained in [R1457], the form that is taken by security labels
      of a protocol's packets varies depending on the OSIRM layer in
      which the protocol operates. Like meta-data generally, a security
      label of a data packet may be either explicit (e.g., IPSO) or
      implicit (e.g., Alice treats all messages received from Bob as
      being labeled "Not For Public Release"). In a connectionless
      protocol, every packet might have an explicit label; but in a
      connection-oriented protocol, all packets might have the same
      implicit label that is determined at the time the connection is
      established.

      Both classified and unclassified system resources may require a
      security label. (See: FOUO.)

   $ security level
      (I) The combination of a hierarchical classification level and a
      set of non-hierarchical category designations that represents how
      sensitive a specified type or item of information is. (See:
      dominate, lattice model. Compare: classification level.)

      Usage: IDOCs that use this term SHOULD state a definition for it.
      The term is usually understood to involve sensitivity to
      disclosure, but it also is used in many other ways and could
      easily be misunderstood.

   $ Security Level field
      (I) A 16-bit field that specifies a security level value in the
      security option (option type 130) of version 4 IP's datagram
      header format.

      Deprecated Abbreviation: IDOCs SHOULD NOT use the abbreviation "S
      field", which is potentially ambiguous.

   $ security management infrastructure (SMI)
      (I) System components and activities that support security policy
      by monitoring and controlling security services and mechanisms,
      distributing security information, and reporting security events.

      Tutorial: The associated functions are as follows [I7498-4]:
      -  Controlling (granting or restricting) access to system
         resources: This includes verifying authorizations and
         identities, controlling access to sensitive security data, and
         modifying access priorities and procedures in the event of
         attacks.
      -  Retrieving (gathering) and archiving (storing) security
         information: This includes logging security events and
         analyzing the log, monitoring and profiling usage, and
         reporting security violations.
      -  Managing and controlling the encryption process: This includes
         performing the functions of key management and reporting on key
         management problems. (See: PKI.)

   $ security marking
      (I) A physical marking that is bound to an instance of a system
      resource and that represents a security label of the resource,
      i.e., that names or designates the value of one or more security-
      relevant attributes of the resource. (Compare: security label.)

      Tutorial: A security label may be represented by various
      equivalent markings depending on the physical form taken by the
      labeled resource. For example, a document could have a marking
      composed of a bit pattern [FP188] when the document is stored
      electronically as a file in a computer, and also a marking of
      printed alphabetic characters when the document is in paper form.

   $ security mechanism
      (I) A method or process (or a device incorporating it) that can be
      used in a system to implement a security service that is provided
      by or within the system. (See: Tutorial under "security policy".
      Compare: security doctrine.)

      Usage: Usually understood to refer primarily to components of
      communication security, computer security, and emanation security.

      Examples: Authentication exchange, checksum, digital signature,
      encryption, and traffic padding.

   $ security model
      (I) A schematic description of a set of entities and relationships
      by which a specified set of security services are provided by or
      within a system. Example: Bell-LaPadula model, OSIRM. (See:
      Tutorial under "security policy".)

   $ security parameters index (SPI)
      1. (I) /IPsec/ A 32-bit identifier used to distinguish among
      security associations that terminate at the same destination (IP
      address) and use the same security protocol (AH or ESP). Carried
      in AH and ESP to enable the receiving system to determine under
      which security association to process a received packet.

      2. (I) /mobile IP/ A 32-bit index identifying a security
      association from among the collection of associations that are
      available between a pair of nodes, for application to mobile IP
      protocol messages that the nodes exchange.

   $ security perimeter
      (I) A physical or logical boundary that is defined for a domain or
      enclave and within which a particular security policy or security
      architecture applies. (See: insider, outsider.)

   $ security policy
      1. (I) A definite goal, course, or method of action to guide and
      determine present and future decisions concerning security in a
      system. [NCS03, R3198] (Compare: certificate policy.)

      2a. (I) A set of policy rules (or principles) that direct how a
      system (or an organization) provides security services to protect
      sensitive and critical system resources. (See: identity-based
      security policy, policy rule, rule-based security policy, rules of
      behavior. Compare: security architecture, security doctrine,
      security mechanism, security model, [R1281].)

      2b. (O) A set of rules to administer, manage, and control access
      to network resources. [R3060, R3198]

      2c. (O) /X.509/ A set of rules laid down by an authority to govern
      the use and provision of security services and facilities.

      2d. (O) /Common Criteria/ A set of rules that regulate how assets
      are managed, protected, and distributed within a TOE.

      Tutorial: Ravi Sandhu suggests that security policy is one of four
      layers of the security engineering process (as shown in the
      following diagram). Each layer provides a different view of
      security, ranging from what services are needed to how services
      are implemented.

         What Security Services
         Should Be Provided?        +- - - - - - - - - - - - -+
         ^  +- - - - - - - - - - - -| Mission Functions View  |
         |  | Security Policy       |- - - - - - - - - - - - -+
         |  +- - - - - - - - - - - -| Domain Practices View   |
         |  | Security Model        |- - - - - - - - - - - - -+
         |  +- - - - - - - - - - - -| Enclave Services View   |
         |  | Security Architecture |- - - - - - - - - - - - -+
         |  +- - - - - - - - - - - -| Agent Mechanisms View   |
         |  | Security Mechanism    |- - - - - - - - - - - - -+
         v  +- - - - - - - - - - - -| Platform Devices View   |
         How Are Security           +- - - - - - - - - - - - -+
         Services Implemented?

      We suggest that each of Sandhu's four layers is a mapping between
      two points of view that differ in their degree of abstraction,
      according to the perspectives of various participants in system
      design, development, and operation activities, as follows:.
      -  Mission functions view: The perspective of a user of system
         resources. States time-phased protection needs for resources
         and identifies sensitive and critical resources -- networks,
         hosts, applications, and databases. Independent of rules and
         practices used to achieve protection.
      -  Domain practices view: The perspective of an enterprise manager
         who sets protection standards for resources. States rules and
         practices for protection. Identifies domain members; i.e.,
         entities (users/providers) and resources (including data
         objects). Independent of system topology. Not required to be
         hierarchical.
      -  Enclave services view: The perspective of a system designer who
         allocates security functions to major components. Assigns
         security services to system topology structures and their

         contents. Independent of security mechanisms. Hierarchical
         across all domains.
      -  Agent mechanisms view: The perspective of a system engineer who
         specifies security mechanisms to implement security services.
         Specifies mechanisms to be used by protocol, database, and
         application engines. Independent of type and manufacture of
         platforms and other physical devices.
      -  Platform devices view: The perspective of an as-built
         description of the system in operation. Specifies exactly how
         to build or assemble the system, and also specifies procedures
         for operating the system.

   $ Security Policy Database (SPD)
      (I) /IPsec/ In an IPsec implementation operating in a network
      node, a database that contains parameters that specify policies
      set by a user or administrator to determine what IPsec services,
      if any, are to be provided to IP datagrams sent or received by the
      node, and in what fashion they are provided. For each datagram,
      the SPD specifies one of three choices: discard the datagram,
      apply IPsec services (e.g., AH or ESP), or bypass IPsec. Separate
      inbound and outbound SPDs are needed because of the directionality
      of IPsec security associations. [R4301] (Compare: SAD.)

   $ Security Protocol 3 (SP3)
      (O) A protocol [SDNS3] developed by SDNS to provide connectionless
      data security at the top of OSIRM Layer 3. (Compare: IPsec, NLSP.)

   $ Security Protocol 4 (SP4)
      (O) A protocol [SDNS4] developed by SDNS to provide either
      connectionless or end-to-end connection-oriented data security at
      the bottom of OSIRM Layer 4. (See: TLSP.)

   $ security-relevant event
      (D) Synonym for "security event".

      Deprecated Term: IDOCs SHOULD NOT use this term; it is wordy.

   $ security-sensitive function
      (D) Synonym for "security function".

      Deprecated Term: IDOCs SHOULD NOT use this term; it is wordy.

   $ security service
      1. (I) A processing or communication service that is provided by a
      system to give a specific kind of protection to system resources.
      (See: access control service, audit service, availability service,
      data confidentiality service, data integrity service, data origin

      authentication service, non-repudiation service, peer entity
      authentication service, system integrity service.)

      Tutorial: Security services implement security policies, and are
      implemented by security mechanisms.

      2. (O) "A service, provided by a layer of communicating open
      systems, [that] ensures adequate security of the systems or the
      data transfers." [I7498-2]

   $ security situation
      (I) /ISAKMP/ The set of all security-relevant information (e.g.,
      network addresses, security classifications, manner of operation
      such as normal or emergency) that is needed to decide the security
      services that are required to protect the association that is
      being negotiated.

   $ security target
      (N) /Common Criteria/ A set of security requirements and
      specifications to be used as the basis for evaluation of an
      identified TOE.

      Tutorial: A security target (ST) is a statement of security claims
      for a particular information technology security product or
      system, and is the basis for agreement among all parties as to
      what security the product or system offers. An ST parallels the
      structure of a protection profile, but has additional elements
      that include product-specific detailed information. An ST contains
      a summary specification, which defines the specific measures taken
      in the product or system to meet the security requirements.

   $ security token
      (I) See: token.

   $ security violation
      (I) An act or event that disobeys or otherwise breaches security
      policy. (See: compromise, penetration, security incident.)

   $ seed
      (I) A value that is an input to a pseudorandom number generator.

   $ selective-field confidentiality
      (I) A data confidentiality service that preserves confidentiality
      for one or more parts (i.e., fields) of each packet. (See:
      selective-field integrity.)

      Tutorial: Data confidentiality service usually is applied to
      entire SDUs, but some situations might require protection of only

      part of each packet. For example, when Alice uses a debit card at
      an automated teller machine (ATM), perhaps only her PIN is
      enciphered for confidentiality when her transaction request is
      transmitted from the ATM to her bank's computer.

      In any given operational situation, there could be many different
      reasons for using selective field confidentiality. In the ATM
      example, there are at least four possibilities: The service may
      provide a fail-safe mode of operation, ensuring that the bank can
      still process transactions (although with some risk) even when the
      encryption system fails. It may make messages easier to work with
      when doing system fault isolation. It may avoid problems with laws
      that prevent shipping enciphered data across international
      borders. It may improve efficiency by reducing processing load at
      a central computer site.

   $ selective-field integrity
      (I) A data integrity service that preserves integrity for one or
      more parts (i.e., fields) of each packet. (See: selective-field
      confidentiality.)

      Tutorial: Data integrity service may be implemented in a protocol
      to protect the SDU part of packets, the PCI part, or both.
      -  SDU protection: When service is provided for SDUs, it usually
         is applied to entire SDUs, but it might be applied only to
         parts of SDUs in some situations. For example, an IPS
         Application-Layer protocol might need protection of only part
         of each packet, and this might enable faster processing.
      -  PCI protection: To prevent active wiretapping, it might be
         desirable to apply data integrity service to the entire PCI,
         but some PCI fields in some protocols need to be mutable in
         transit. For example, the "Time to Live" field in IPv4 is
         changed each time a packet passes through a router in the
         Internet Layer. Thus, the value that the field will have when
         the packet arrives at its destination is not predictable by the
         sender and cannot be included in a checksum computed by the
         sender. (See: Authentication Header.)

   $ self-signed certificate
      (I) A public-key certificate for which the public key bound by the
      certificate and the private key used to sign the certificate are
      components of the same key pair, which belongs to the signer.
      (Compare: root certificate.)

      Tutorial: In a self-signed X.509 public-key certificate, the
      issuer's DN is the same as the subject's DN.

   $ semantic security
      (I) An attribute of an encryption algorithm that is a
      formalization of the notion that the algorithm not only hides the
      plain text but also reveals no partial information about the plain
      text; i.e., whatever is computable about the plain text when given
      the cipher text, is also computable without the cipher text.
      (Compare: indistinguishability.)

   $ semiformal
      (I) Expressed in a restricted syntax language with defined
      semantics. [CCIB] (Compare: formal, informal.)

   $ sensitive
      (I) A condition of a system resource such that the loss of some
      specified property of that resource, such as confidentiality or
      integrity, would adversely affect the interests or business of its
      owner or user. (See: sensitive information. Compare: critical.)

   $ sensitive compartmented information (SCI)
      (O) /U.S. Government/ Classified information concerning or derived
      from intelligence sources, methods, or analytical processes, which
      is required to be handled within formal control systems
      established by the Director of Central Intelligence. [C4009] (See:
      compartment, SAP, SCIF. Compare: collateral information.)

   $ sensitive compartmented information facility (SCIF)
      (O) /U.S. Government/ "An accredited area, room, group of rooms,
      building, or installation where SCI may be stored, used,
      discussed, and/or processed." [C4009] (See: SCI. Compare: shielded
      enclosure.)

   $ sensitive information
      1. (I) Information for which (a) disclosure, (b) alteration, or
      (c) destruction or loss could adversely affect the interests or
      business of its owner or user. (See: data confidentiality, data
      integrity, sensitive. Compare: classified, critical.)

      2. (O) /U.S. Government/ Information for which (a) loss, (b)
      misuse, (c) unauthorized access, or (d) unauthorized modification
      could adversely affect the national interest or the conduct of
      federal programs, or the privacy to which individuals are entitled
      under the Privacy Act of 1974, but that has not been specifically
      authorized under criteria established by an Executive Order or an
      Act of Congress to be kept classified in the interest of national
      defense or foreign policy.

      Tutorial: Systems that are not U.S. national security systems, but
      contain sensitive U.S. Federal Government information, must be

      protected according to the Computer Security Act of 1987 (Public
      Law 100-235). (See: national security.)

   $ sensitivity label
      (D) Synonym for "classification label".

      Deprecated term: IDOCs SHOULD NOT use this term because the
      definition of "sensitive" involves not only data confidentiality,
      but also data integrity.

   $ sensitivity level
      (D) Synonym for "classification level".

      Deprecated term: IDOCs SHOULD NOT use this term because the
      definition of "sensitive" involves not only data confidentiality,
      but also data integrity.

   $ separation of duties
      (I) The practice of dividing the steps in a system process among
      different individual entities (i.e., different users or different
      roles) so as to prevent a single entity acting alone from being
      able to subvert the process. Usage: a.k.a. "separation of
      privilege". (See: administrative security, dual control.)

   $ serial number
      See: certificate serial number.

   $ Serpent
      (O) A symmetric, 128-bit block cipher designed by Ross Anderson,
      Eli Biham, and Lars Knudsen as a candidate for the AES.

   $ server
      (I) A system entity that provides a service in response to
      requests from other system entities called clients.

   $ service data unit (SDU)
      (N) See: secondary definition under "protocol data unit".

   $ session
      1a. (I) /computer usage/ A continuous period of time, usually
      initiated by a login, during which a user accesses a computer
      system.

      1b. (I) /computer activity/ The set of transactions or other
      computer activities that are performed by or for a user during a
      period of computer usage.

      2. (I) /access control/ A temporary mapping of a principal to one
      or more roles. (See: role-based access control.)

      Tutorial: A user establishes a session as a principal and
      activates some subset of roles to which the principal has been
      assigned. The authorizations available to the principal in the
      session are the union of the permissions of all the roles
      activated in the session. Each session is associated with a single
      principal and, therefore, with a single user. A principal may have
      multiple, concurrent sessions and may activate a different set of
      roles in each session.

      3. (I) /computer network/ A persistent but (normally) temporary
      association between a user agent (typically a client) and a second
      process (typically a server). The association may persist across
      multiple exchanges of data, including multiple connections.
      (Compare: security association.)

   $ session key
      (I) In the context of symmetric encryption, a key that is
      temporary or is used for a relatively short period of time. (See:
      ephemeral, KDC, session. Compare: master key.)

      Tutorial: A session key is used for a defined period of
      communication between two system entities or components, such as
      for the duration of a single connection or transaction set; or the
      key is used in an application that protects relatively large
      amounts of data and, therefore, needs to be rekeyed frequently.

   $ SET(trademark)
      (O) See: SET Secure Electronic Transaction(trademark).

   $ SET private extension
      (O) One of the private extensions defined by SET for X.509
      certificates. Carries information about hashed root key,
      certificate type, merchant data, cardholder certificate
      requirements, encryption support for tunneling, or message support
      for payment instructions.

   $ SET qualifier
      (O) A certificate policy qualifier that provides information about
      the location and content of a SET certificate policy.

      Tutorial: Besides the policies and qualifiers inherited from its
      own certificate, each CA in the SET certification hierarchy may
      add one qualifying statement to the root policy when the CA issues
      a certificate. The additional qualifier is a certificate policy
      for that CA. Each policy in a SET certificate may have these

      qualifiers: (a) a URL where a copy of the policy statement may be
      found; (b) an electronic mail address where a copy of the policy
      statement may be found; (c) a hash result of the policy statement,
      computed using the indicated algorithm; and (d) a statement
      declaring any disclaimers associated with the issuing of the
      certificate.

   $ SET Secure Electronic Transaction(trademark) or SET(trademark)
      (N) A protocol developed jointly by MasterCard International and
      Visa International and published as an open standard to provide
      confidentiality of transaction information, payment integrity, and
      authentication of transaction participants for payment card
      transactions over unsecured networks, such as the Internet. [SET1]
      (See: acquirer, brand, cardholder, dual signature, electronic
      commerce, IOTP, issuer, merchant, payment gateway, third party.)

      Tutorial: This term and acronym are trademarks of SETCo.
      MasterCard and Visa announced the SET standard on 1 February 1996.

   $ SETCo
      (O) Abbreviation of "SET Secure Electronic Transaction LLC",
      formed on 19 December 1997 by MasterCard and Visa for implementing
      the SET Secure Electronic Transaction(trademark) standard. A later
      memorandum of understanding added American Express and JCB Credit
      Card Company as co-owners of SETCo.

   $ SHA, SHA-1, SHA-2
      (N) See: Secure Hash Algorithm.

   $ shared identity
      (I) See: secondary definition under "identity".

   $ shared secret
      (D) Synonym for "cryptographic key" or "password".

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the term is used in many ways and could
      easily be misunderstood.

   $ shielded enclosure
      (O) "Room or container designed to attenuate electromagnetic
      radiation, acoustic signals, or emanations." [C4009] (See:
      emanation. Compare: SCIF.)

   $ short title
      (O) "Identifying combination of letters and numbers assigned to
      certain items of COMSEC material to facilitate handling,
      accounting, and controlling." [C4009] (Compare: KMID, long title.)

   $ shroud
      (D) /verb/ To encrypt a private key, possibly in concert with a
      policy that prevents the key from ever being available in
      cleartext form beyond a certain, well-defined security perimeter.
      [PKC12] (See: encrypt. Compare: seal, wrap.)

      Deprecated Term: IDOCs SHOULD NOT use this term as defined here;
      the definition duplicates the meaning of other, standard terms.
      Instead, use "encrypt" or other terminology that is specific with
      regard to the mechanism being used.

   $ SHS
      (N) See: Secure Hash Standard.

   $ sign
      (I) Create a digital signature for a data object. (See: signer.)

   $ signal analysis
      (I) Gaining indirect knowledge (inference) of communicated data by
      monitoring and analyzing a signal that is emitted by a system and
      that contains the data but is not intended to communicate the
      data. (See: emanation. Compare: traffic analysis.)

   $ signal intelligence
      (I) The science and practice of extracting information from
      signals. (See: signal security.)

   $ signal security
      (N) (I) The science and practice of protecting signals. (See:
      cryptology, security.)

      Tutorial: The term "signal" denotes (a) communication in almost
      any form and also (b) emanations for other purposes, such as
      radar. Signal security is opposed by signal intelligence, and each
      discipline includes opposed sub-disciplines as follows [Kahn]:

      Signal Security                 Signal Intelligence
      ------------------------------  ---------------------------------
      1. Communication Security       1. Communication Intelligence
         1a. Cryptography                1a. Cryptanalysis
         1b. Traffic Security            1b. Traffic Analysis
         1c. Steganography               1c. Detection and Interception
      2. Electronic Security          2. Electronic Intelligence
         2a. Emission Security           2a. Electronic Reconnaissance
         2b. Counter-Countermeasures     2b. Countermeasures
      ------------------------------  ---------------------------------

   $ signature
      (O) A symbol or process adopted or executed by a system entity
      with present intention to declare that a data object is genuine.
      (See: digital signature, electronic signature.)

   $ signature certificate
      (I) A public-key certificate that contains a public key that is
      intended to be used for verifying digital signatures, rather than
      for encrypting data or performing other cryptographic functions.

      Tutorial: A v3 X.509 public-key certificate may have a "keyUsage"
      extension that indicates the purpose for which the certified
      public key is intended. (See: certificate profile.)

   $ signed receipt
      (I) An S/MIME service [R2634] that (a) provides, to the originator
      of a message, proof of delivery of the message and (b) enables the
      originator to demonstrate to a third party that the recipient was
      able to verify the signature of the original message.

      Tutorial: The receipt is bound to the original message by a
      signature; consequently, the service may be requested only for a
      message that is signed. The receipt sender may optionally also
      encrypt the receipt to provide confidentiality between the receipt
      sender and the receipt recipient.

   $ signer
      (N) A human being or organization entity that uses a private key
      to sign (i.e., create a digital signature on) a data object. [DSG]

   $ SILS
      (N) See: Standards for Interoperable LAN/MAN Security.

   $ simple authentication
      1. (I) An authentication process that uses a password as the
      information needed to verify an identity claimed for an entity.
      (Compare: strong authentication.)

      2. (O) "Authentication by means of simple password arrangements."
      [X509]

   $ Simple Authentication and Security Layer (SASL)
      (I) An Internet specification [R2222, R4422] for adding
      authentication service to connection-based protocols. (Compare:
      EAP, GSS-API.)

      Tutorial: To use SASL, a protocol includes a command for
      authenticating a user to a server and for optionally negotiating
      protection of subsequent protocol interactions. The command names
      a registered security mechanism. SASL mechanisms include Kerberos,
      GSS-API, S/KEY, and others. Some protocols that use SASL are IMAP4
      and POP3.

   $ Simple Key Management for Internet Protocols (SKIP)
      (I) A key-distribution protocol that uses hybrid encryption to
      convey session keys that are used to encrypt data in IP packets.
      (See:  SKIP reference in [R2356].)

      Tutorial: SKIP was designed by Ashar Aziz and Whitfield Diffie at
      Sun Microsystems and proposed as the standard key management
      protocol for IPsec, but IKE was chosen instead. Although IKE is
      mandatory for an IPsec implementation, the use of SKIP is not
      excluded.

      SKIP uses the Diffie-Hellman-Merkle algorithm (or could use
      another key-agreement algorithm) to generate a key-encrypting key
      for use between two entities. A session key is used with a
      symmetric algorithm to encrypt data in one or more IP packets that
      are to be sent from one entity to the other. A symmetric KEK is
      established and used to encrypt the session key, and the encrypted
      session key is placed in a SKIP header that is added to each IP
      packet that is encrypted with that session key.

   $ Simple Mail Transfer Protocol (SMTP)
      (I) A TCP-based, Application-Layer, Internet Standard protocol
      (RFC 821) for moving electronic mail messages from one computer to
      another.

   $ Simple Network Management Protocol (SNMP)
      (I) A (usually) UDP-based, Application-Layer, Internet Standard
      protocol (RFCs 3410-3418) for conveying management information
      between system components that act as managers and agents.

   $ Simple Public Key Infrastructure (SPKI)
      (I) A set of experimental concepts (RFCs 2692, 2693) that were
      proposed as alternatives to the concepts standardized in PKIX.

   $ simple security property
      (N) /formal model/ Property of a system whereby a subject has read
      access to an object only if the clearance of the subject dominates
      the classification of the object. See: Bell-LaPadula model.

   $ single sign-on
      1. (I) An authentication subsystem that enables a user to access
      multiple, connected system components (such as separate hosts on a
      network) after a single login at only one of the components. (See:
      Kerberos.)

      2. (O) /Liberty Alliance/ A security subsystem that enables a user
      identity to be authenticated at an identity provider -- i.e., at a
      service that authenticates and asserts the user's identity -- and
      then have that authentication be honored by other service
      providers.

      Tutorial: A single sign-on subsystem typically requires a user to
      log in once at the beginning of a session, and then during the
      session transparently grants access by the user to multiple,
      separately protected hosts, applications, or other system
      resources, without further login action by the user (unless, of
      course, the user logs out). Such a subsystem has the advantages of
      being user friendly and enabling authentication to be managed
      consistently across an entire enterprise. Such a subsystem also
      has the disadvantage of requiring all the accessed components to
      depend on the security of the same authentication information.

   $ singular identity
      (I) See: secondary definition under "identity".

   $ site
      (I) A facility -- i.e., a physical space, room, or building
      together with its physical, personnel, administrative, and other
      safeguards -- in which system functions are performed. (See:
      node.)

   $ situation
      (I) See: security situation.

   $ SKEME
      (I) A key-distribution protocol from which features were adapted
      for IKE. [SKEME]

   $ SKIP
      (I) See: Simple Key Management for Internet Protocols.

   $ SKIPJACK
      (N) A type 2, 64-bit block cipher [SKIP, R2773] with a key size of
      80 bits. (See: CAPSTONE, CLIPPER, FORTEZZA, Key Exchange
      Algorithm.)

      Tutorial: SKIPJACK was developed by NSA and formerly classified at
      the U.S. DoD "Secret" level. On 23 June 1998, NSA announced that
      SKIPJACK had been declassified.

   $ slot
      (O) /MISSI/ One of the FORTEZZA PC card storage areas that are
      each able to hold an X.509 certificate plus other data, including
      the private key that is associated with a public-key certificate.

   $ smart card
      (I) A credit-card sized device containing one or more integrated
      circuit chips that perform the functions of a computer's central
      processor, memory, and input/output interface. (See: PC card,
      smart token.)

      Usage: Sometimes this term is used rather strictly to mean a card
      that closely conforms to the dimensions and appearance of the kind
      of plastic credit card issued by banks and merchants. At other
      times, the term is used loosely to include cards that are larger
      than credit cards, especially cards that are thicker, such as PC
      cards.

   $ smart token
      (I) A device that conforms to the definition of "smart card"
      except that rather than having the standard dimensions of a credit
      card, the token is packaged in some other form, such as a military
      dog tag or a door key. (See: smart card, cryptographic token.)

   $ SMI
      (I) See: security management infrastructure.

   $ SMTP
      (I) See: Simple Mail Transfer Protocol.

   $ smurf attack
      (D) /slang/ A denial-of-service attack that uses IP broadcast
      addressing to send ICMP ping packets with the intent of flooding a
      system. (See: fraggle attack, ICMP flood.)

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term.

      Derivation: The Smurfs are a fictional race of small, blue
      creatures that were created by a cartoonist. Perhaps the inventor
      of this attack thought that a swarm of ping packets resembled a
      gang of smurfs. (See: Deprecated Usage under "Green Book".)

      Tutorial: The attacker sends ICMP echo request ("ping") packets
      that appear to originate not from the attacker's own IP address,
      but from the address of the host or router that is the target of
      the attack. Each packet is addressed to an IP broadcast address,
      e.g., to all IP addresses in a given network. Thus, each echo
      request that is sent by the attacker results in many echo
      responses being sent to the target address. This attack can
      disrupt service at a particular host, at the hosts that depend on
      a particular router, or in an entire network.

   $ sneaker net
      (D) /slang/ A process that transfers data between systems only
      manually, under human control; i.e., a data transfer process that
      involves an air gap.

      Deprecated Term: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term.

   $ Snefru
      (N) A public-domain, cryptographic hash function (a.k.a. "The
      Xerox Secure Hash Function") designed by Ralph C. Merkle at Xerox
      Corporation. Snefru can produce either a 128-bit or 256-bit output
      (i.e., hash result). [Schn] (See: Khafre, Khufu.)

   $ sniffing
      (D) /slang/ Synonym for "passive wiretapping"; most often refers
      to capturing and examining the data packets carried on a LAN.
      (See: password sniffing.)

      Deprecated Term: IDOCs SHOULD NOT use this term; it unnecessarily
      duplicates the meaning of a term that is better established. (See:
      Deprecated Usage under "Green Book".

   $ SNMP
      (I) See: Simple Network Management Protocol.

   $ social engineering
      (D) Euphemism for non-technical or low-technology methods, often
      involving trickery or fraud, that are used to attack information
      systems. Example: phishing.

      Deprecated Term: IDOCs SHOULD NOT use this term; it is too vague.
      Instead, use a term that is specific with regard to the means of
      attack, e.g., blackmail, bribery, coercion, impersonation,
      intimidation, lying, or theft.

   $ SOCKS
      (I) An Internet protocol [R1928] that provides a generalized proxy
      server that enables client-server applications (e.g., TELNET, FTP,
      or HTTP; running over either TCP or UDP) to use the services of a
      firewall.

      Tutorial: SOCKS is layered under the IPS Application Layer and
      above the Transport Layer. When a client inside a firewall wishes
      to establish a connection to an object that is reachable only
      through the firewall, it uses TCP to connect to the SOCKS server,
      negotiates with the server for the authentication method to be
      used, authenticates with the chosen method, and then sends a relay
      request. The SOCKS server evaluates the request, typically based
      on source and destination addresses, and either establishes the
      appropriate connection or denies it.

   $ soft TEMPEST
      (O) The use of software techniques to reduce the radio frequency
      information leakage from computer displays and keyboards. [Kuhn]
      (See: TEMPEST.)

   $ soft token
      (D) A data object that is used to control access or authenticate
      authorization. (See: token.)

      Deprecated Term: IDOCs SHOULD NOT use this term as defined here;
      the definition duplicates the meaning of other, standard terms.
      Instead, use "attribute certificate" or another term that is
      specific with regard to the mechanism being used.

   $ software
      (I) Computer programs (which are stored in and executed by
      computer hardware) and associated data (which also is stored in
      the hardware) that may be dynamically written or modified during
      execution. (Compare: firmware.)

   $ software error
      (I) /threat action/ See: secondary definitions under "corruption",
      "exposure", and "incapacitation".

   $ SORA
      (O) See: SSO-PIN ORA.

   $ source authentication
      (D) Synonym for "data origin authentication" or "peer entity
      authentication". (See: data origin authentication, peer entity
      authentication).

      Deprecated Term: IDOCs SHOULD NOT use this term because it is
      ambiguous and, in either meaning, duplicates the meaning of
      internationally standardized terms. If the intent is to
      authenticate the original creator or packager of data received,
      then use "data origin authentication". If the intent is to
      authenticate the identity of the sender of data in the current
      instance, then use "peer entity authentication".

   $ source integrity
      (I) The property that data is trustworthy (i.e., worthy of
      reliance or trust), based on the trustworthiness of its sources
      and the trustworthiness of any procedures used for handling data
      in the system. Usage: a.k.a. Biba integrity. (See: integrity.
      Compare: correctness integrity, data integrity.)

      Tutorial: For this kind of integrity, there are formal models of
      unauthorized modification (see: Biba model) that logically
      complement the more familiar models of unauthorized disclosure
      (see: Bell-LaPadula model). In these models, objects are labeled
      to indicate the credibility of the data they contain, and there
      are rules for access control that depend on the labels.

   $ SP3
      (O) See: Security Protocol 3.

   $ SP4
      (O) See: Security Protocol 4.

   $ spam
      1a. (I) /slang verb/ To indiscriminately send unsolicited,
      unwanted, irrelevant, or inappropriate messages, especially
      commercial advertising in mass quantities.

      1b. (I) /slang noun/ Electronic "junk mail". [R2635]

      Deprecated Usage: IDOCs SHOULD NOT use this term in uppercase
      letters, because SPAM(trademark) is a trademark of Hormel Foods
      Corporation. Hormel says, "We do not object to use of this slang
      term [spam] to describe [unsolicited advertising email], although
      we do object to the use of our product image in association with
      that term. Also, if the term is to be used, it SHOULD be used in
      all lower-case letters to distinguish it from our trademark SPAM,
      which SHOULD be used with all uppercase letters." (See: metadata.)

      Tutorial: In sufficient volume, spam can cause denial of service.
      (See: flooding.) According to Hormel, the term was adopted as a
      result of a Monty Python skit in which a group of Vikings sang a
      chorus of 'SPAM, SPAM, SPAM ...' in an increasing crescendo,

      drowning out other conversation. This lyric became a metaphor for
      the unsolicited advertising messages that threaten to overwhelm
      other discourse on the Internet.

   $ SPD
      (I) See: Security Policy Database.

   $ special access program (SAP)
      (O) /U.S. Government/ "Sensitive program, [that is] approved in
      writing by a head of agency with [i.e., who has] original top
      secret classification authority, [and] that imposes need-to-know
      and access controls beyond those normally provided for access to
      Confidential, Secret, or Top Secret information. The level of
      controls is based on the criticality of the program and the
      assessed hostile intelligence threat. The program may be an
      acquisition program, an intelligence program, or an operations and
      support program." [C4009] (See: formal access approval, SCI.
      Compare: collateral information.)

   $ SPI
      (I) See: Security Parameters Index.

   $ SPKI
      (I) See: Simple Public Key Infrastructure.

   $ split key
      (I) A cryptographic key that is generated and distributed as two
      or more separate data items that individually convey no knowledge
      of the whole key that results from combining the items. (See: dual
      control, split knowledge.)

   $ split knowledge
      1. (I) A security technique in which two or more entities
      separately hold data items that individually do not convey
      knowledge of the information that results from combining the
      items. (See: dual control, split key.)

      2. (O) "A condition under which two or more entities separately
      have key components [that] individually convey no knowledge of the
      plaintext key [that] will be produced when the key components are
      combined in the cryptographic module." [FP140]

   $ spoof
      (I) /threat action/ See: secondary definition under "masquerade".

   $ spoofing attack
      (I) Synonym for "masquerade attack".

   $ spread spectrum
      (N) A TRANSEC technique that transmits a signal in a bandwidth
      much greater than the transmitted information needs. [F1037]
      Example: frequency hopping.

      Tutorial: Usually uses a sequential, noise-like signal structure
      to spread the normally narrowband information signal over a
      relatively wide band of frequencies. The receiver correlates the
      signals to retrieve the original information signal. This
      technique decreases potential interference to other receivers,
      while achieving data confidentiality and increasing immunity of
      spread spectrum receivers to noise and interference.

   $ spyware
      (D) /slang/ Software that an intruder has installed
      surreptitiously on a networked computer to gather data from that
      computer and send it through the network to the intruder or some
      other interested party. (See: malicious logic, Trojan horse.)

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the term is used in many ways and could
      easily be misunderstood.

      Tutorial: Some examples of the types of data that might be
      gathered by spyware are application files, passwords, email
      addresses, usage histories, and keystrokes. Some examples of
      motivations for gathering the data are blackmail, financial fraud,
      identity theft, industrial espionage, market research, and
      voyeurism.

   $ SSH(trademark)
      (N) See: Secure Shell(trademark).

   $ SSL
      (I) See: Secure Sockets Layer.

   $ SSO
      (I) See: system security officer.

   $ SSO PIN
      (O) /MISSI/ One of two PINs that control access to the functions
      and stored data of a FORTEZZA PC card. Knowledge of the SSO PIN
      enables a card user to perform the FORTEZZA functions intended for
      use by an end user and also the functions intended for use by a
      MISSI CA. (See: user PIN.)

   $ SSO-PIN ORA (SORA)
      (O) /MISSI/ A MISSI organizational RA that operates in a mode in
      which the ORA performs all card management functions and,
      therefore, requires knowledge of the SSO PIN for FORTEZZA PC cards
      issued to end users.

   $ Standards for Interoperable LAN/MAN Security (SILS)
      1. (N) The IEEE 802.10 standards committee. (See: [FP191].)

      2. (N) A set of IEEE standards, which has eight parts: (a) Model,
      including security management, (b) Secure Data Exchange protocol,
      (c) Key Management, (d) [has been incorporated in (a)], (e) SDE
      Over Ethernet 2.0, (f) SDE Sublayer Management, (g) SDE Security
      Labels, and (h) SDE PICS Conformance. Parts b, e, f, g, and h are
      incorporated in IEEE Standard 802.10-1998.

   $ star property
      (N) See: *-property.

   $ Star Trek attack
      (D) /slang/ An attack that penetrates your system where no attack
      has ever gone before.

      Deprecated Usage: IDOCs SHOULD NOT use this term; it is a joke for
      Trekkies. (See: Deprecated Usage under "Green Book".)

   $ static
      (I) /adjective/ Refers to a cryptographic key or other parameter
      that is relatively long-lived. (Compare: ephemeral.)

   $ steganography
      (I) Methods of hiding the existence of a message or other data.
      This is different than cryptography, which hides the meaning of a
      message but does not hide the message itself. Examples: For
      classic, physical methods, see [Kahn]; for modern, digital
      methods, see [John]. (See: cryptology. Compare: concealment
      system, digital watermarking.)

   $ storage channel
      (I) See: covert storage channel.

   $ storage key
      (I) A cryptographic key used by a device for protecting
      information that is being maintained in the device, as opposed to
      protecting information that is being transmitted between devices.
      (See: cryptographic token, token copy. Compare: traffic key.)

   $ stream cipher
      (I) An encryption algorithm that breaks plain text into a stream
      of successive elements (usually, bits) and encrypts the n-th
      plaintext element with the n-th element of a parallel key stream,
      thus converting the plaintext stream into a ciphertext stream.
      [Schn] (See: block cipher.)

   $ stream integrity service
      (I) A data integrity service that preserves integrity for a
      sequence of data packets, including both (a) bit-by-bit datagram
      integrity of each individual packet in the set and (b) packet-by-
      packet sequential integrity of the set as a whole. (See: data
      integrity. Compare: datagram integrity service.)

      Tutorial: Some internetwork applications need only datagram
      integrity, but others require that an entire stream of packets be
      protected against insertion, reordering, deletion, and delay:
      -  "Insertion": The destination receives an additional packet that
         was not sent by the source.
      -  "Reordering": The destination receives packets in a different
         order than that in which they were sent by the source.
      -  "Deletion": A packet sent by the source is not ever delivered
         to the intended destination.
      -  "Delay": A packet is detained for some period of time at a
         relay, thus hampering and postponing the packet's normal timely
         delivery from source to destination.

   $ strength
      1. (I) /cryptography/ A cryptographic mechanism's level of
      resistance to attacks [R3766]. (See: entropy, strong, work
      factor.)

      2. (N) /Common Criteria/ "Strength of function" is a
      "qualification of a TOE security function expressing the minimum
      efforts assumed necessary to defeat its expected security behavior
      by directly attacking its underlying security mechanisms": (See:
      strong.)
      -  Basic: "A level of the TOE strength of function where analysis
         shows that the function provides adequate protection against
         casual breach of TOE security by attackers possessing a low
         attack potential."
      -  Medium: "... against straightforward or intentional breach ...
         by attackers possessing a moderate attack potential."
      -  High: "... against deliberately planned or organized breach ...
         by attackers possessing a high attack potential."

   $ strong
      1. (I) /cryptography/ Used to describe a cryptographic algorithm
      that would require a large amount of computational power to defeat
      it. (See: strength, work factor, weak key.)

      2. (I) /COMPUSEC/ Used to describe a security mechanism that would
      be difficult to defeat. (See: strength, work factor.)

   $ strong authentication
      1. (I) An authentication process that uses a cryptographic
      security mechanism -- particularly public-key certificates -- to
      verify the identity claimed for an entity. (Compare: simple
      authentication.)

      2. (O) "Authentication by means of cryptographically derived
      credentials." [X509]

   $ subject
      1a. (I) A process in a computer system that represents a principal
      and that executes with the privileges that have been granted to
      that principal. (Compare: principal, user.)

      1b. (I) /formal model/ A system entity that causes information to
      flow among objects or changes the system state; technically, a
      process-domain pair. A subject may itself be an object relative to
      some other subject; thus, the set of subjects in a system is a
      subset of the set of objects. (See: Bell-LaPadula model, object.)

      2. (I) /digital certificate/ The name (of a system entity) that is
      bound to the data items in a digital certificate; e.g., a DN that
      is bound to a key in a public-key certificate. (See: X.509.)

   $ subject CA
      (D) The CA that is the subject of a cross-certificate issued by
      another CA. [X509] (See: cross-certification.)

      Deprecated Term: IDOCs SHOULD NOT use this term because it is not
      widely known and could be misunderstood. Instead, say "the CA that
      is the subject of the cross-certificate".

   $ subnetwork
      (N) An OSI term for a system of packet relays and connecting links
      that implement OSIRM layer 2 or 3 to provide a communication
      service that interconnects attached end systems. Usually, the
      relays are all of the same type (e.g., X.25 packet switches, or
      interface units in an IEEE 802.3 LAN). (See: gateway, internet,
      router.)

   $ subordinate CA (SCA)
      1. (I) A CA whose public-key certificate is issued by another
      (superior) CA. (See: certification hierarchy. Compare: cross-
      certification.)

      2. (O) /MISSI/ The fourth-highest (i.e., bottom) level of a MISSI
      certification hierarchy; a MISSI CA whose public-key certificate
      is signed by a MISSI CA rather than by a MISSI PCA. A MISSI SCA is
      the administrative authority for a subunit of an organization,
      established when it is desirable to organizationally distribute or
      decentralize the CA service. The term refers both to that
      authoritative office or role, and to the person who fills that
      office. A MISSI SCA registers end users and issues their
      certificates and may also register ORAs, but may not register
      other CAs. An SCA periodically issues a CRL.

   $ subordinate DN
      (I) An X.500 DN is subordinate to another X.500 DN if it begins
      with a set of attributes that is the same as the entire second DN
      except for the terminal attribute of the second DN (which is
      usually the name of a CA). For example, the DN <C=FooLand, O=Gov,
      OU=Treasurer, CN=DukePinchpenny> is subordinate to the DN
      <C=FooLand, O=Gov, CN=KingFooCA>.

   $ subscriber
      (I) /PKI/ A user that is registered in a PKI and, therefore, can
      be named in the "subject" field of a certificate issued by a CA in
      that PKI. (See: registration, user.)

      Usage: This term is needed to distinguish registered users from
      two other kinds of PKI users:
      -  Users that access the PKI but are not identified to it: For
         example, a relying party may access a PKI repository to obtain
         the certificate of some other party. (See: access.)
      -  Users that do not access the PKI: For example, a relying party
         (see: certificate user) may use a digital certificate that was
         obtained from a database that is not part of the PKI that
         issued the certificate.

   $ substitution
      1. (I) /cryptography/ A method of encryption in which elements of
      the plain text retain their sequential position but are replaced
      by elements of cipher text. (Compare: transposition.)

      2. (I) /threat action/ See: secondary definition under
      "falsification".

   $ subsystem
      (I) A collection of related system components that together
      perform a system function or deliver a system service.

   $ superencryption
      (I) An encryption operation for which the plaintext input to be
      transformed is the ciphertext output of a previous encryption
      operation. (Compare: hybrid encryption.)

   $ superuser
      (I) /UNIX/ Synonym for "root".

   $ survivability
      (I) The ability of a system to remain in operation or existence
      despite adverse conditions, including natural occurrences,
      accidental actions, and attacks. (Compare: availability,
      reliability.)

   $ swIPe
      (I) An encryption protocol for IP that provides confidentiality,
      integrity, and authentication and can be used for both end-to-end
      and intermediate-hop security. [Ioan] (Compare: IPsec.)

      Tutorial: The swIPe protocol is an IP predecessor that is
      concerned only with encryption mechanisms; policy and key
      management are handled outside the protocol.

   $ syllabary
      (N) /encryption/ A list of individual letters, combinations of
      letters, or syllables, with their equivalent code groups, used for
      spelling out proper names or other unusual words that are not
      present in the basic vocabulary (i.e., are not in the codebook) of
      a code used for encryption.

   $ symmetric cryptography
      (I) A branch of cryptography in which the algorithms use the same
      key for both of two counterpart cryptographic operations (e.g.,
      encryption and decryption). (See: asymmetric cryptography.
      Compare: secret-key cryptography.)

      Tutorial: Symmetric cryptography has been used for thousands of
      years [Kahn]. A modern example is AES.

      Symmetric cryptography has a disadvantage compared to asymmetric
      cryptography with regard to key distribution. For example, when
      Alice wants to ensure confidentiality for data she sends to Bob,
      she encrypts the data with a key, and Bob uses the same key to
      decrypt. However, keeping the shared key secret entails both cost

      and risk when the key is distributed to both Alice and Bob. (See:
      key distribution, key management.)

   $ symmetric key
      (I) A cryptographic key that is used in a symmetric cryptographic
      algorithm. (See: symmetric cryptography.)

   $ SYN flood
      (I) A denial-of-service attack that sends a large number of TCP
      SYN (synchronize) packets to a host with the intent of disrupting
      the operation of that host. (See: blind attack, flooding.)

      Tutorial: This attack seeks to exploit a vulnerability in the TCP
      specification or in a TCP implementation. Normally, two hosts use
      a three-way exchange of packets to establish a TCP connection: (a)
      host 1 requests a connection by sending a SYN packet to host 2;
      (b) host 2 replies by sending a SYN-ACK (acknowledgement) packet
      to host 1; and (c) host 1 completes the connection by sending an
      ACK packet to host 2. To attack host 2, host 1 can send a series
      of TCP SYNs, each with a different phony source address. ([R2827]
      discusses how to use packet filtering to prevent such attacks from
      being launched from behind an Internet service provider's
      aggregation point.) Host 2 treats each SYN as a request from a
      separate host, replies to each with a SYN-ACK, and waits to
      receive the matching ACKs. (The attacker can use random or
      unreachable sources addresses in the SYN packets, or can use
      source addresses that belong to third parties, that then become
      secondary victims.)

      For each SYN-ACK that is sent, the TCP process in host 2 needs
      some memory space to store state information while waiting for the
      matching ACK to be returned. If the matching ACK never arrives at
      host 2, a timer associated with the pending SYN-ACK will
      eventually expire and release the space. But if host 1 (or a
      cooperating group of hosts) can rapidly send many SYNs to host 2,
      host 2 will need to store state information for many pending SYN-
      ACKs and may run out of space. This can prevent host 2 from
      responding to legitimate connection requests from other hosts or
      even, if there are flaws in host 2's TCP implementation, crash
      when the available space is exhausted.

   $ synchronization
      (I) Any technique by which a receiving (decrypting) cryptographic
      process attains an internal state that matches the transmitting
      (encrypting) process, i.e., has the appropriate keying material to
      process the cipher text and is correctly initialized to do so.

   $ system
      (I) Synonym for "information system".

      Usage: This is a generic definition, and is the one with which the
      term is used in this Glossary. However, IDOCs that use the term,
      especially IDOCs that are protocol specifications, SHOULD state a
      more specific definition. Also, IDOCs that specify security
      features, services, and assurances need to define which system
      components and system resources are inside the applicable security
      perimeter and which are outside. (See: security architecture.)

   $ system architecture
      (N) The structure of system components, their relationships, and
      the principles and guidelines governing their design and evolution
      over time. [DoD10] (Compare: security architecture.)

   $ system component
      1. (I) A collection of system resources that (a) forms a physical
      or logical part of the system, (b) has specified functions and
      interfaces, and (c) is treated (e.g., by policies or
      specifications) as existing independently of other parts of the
      system. (See: subsystem.)

      2. (O) /ITSEC/ An identifiable and self-contained part of a TOE.

      Usage: Component is a relative term because components may be
      nested; i.e., one component of a system may be a part of another
      component of that system.

      Tutorial: Components can be characterized as follows:
      -  A "physical component" has mass and takes up space.
      -  A "logical component" is an abstraction used to manage and
         coordinate aspects of the physical environment, and typically
         represents a set of states or capabilities of the system.

   $ system entity
      (I) An active part of a system -- a person, a set of persons
      (e.g., some kind of organization), an automated process, or a set
      of processes (see: subsystem) -- that has a specific set of
      capabilities. (Compare: subject, user.)

   $ system high
      (I) The highest security level at which a system operates, or is
      capable of operating, at a particular time or in a particular
      environment. (See: system-high security mode.)

   $ system-high security mode
      (I) A mode of system operation wherein all users having access to
      the system possess all necessary authorizations (both security
      clearance and formal access approval) for all data handled by the
      system, but some users might not have need-to-know for all the
      data. (See: /system operation/ under "mode", formal access
      approval, protection level, security clearance.)

      Usage: Usually abbreviated as "system-high mode". This mode was
      defined in U.S. DoD policy that applied to system accreditation,
      but the term is widely used outside the Government.

   $ system integrity
      1. (I) An attribute or quality "that a system has when it can
      perform its intended function in a unimpaired manner, free from
      deliberate or inadvertent unauthorized manipulation." [C4009,
      NCS04] (See: recovery, system integrity service.)

      2. (D) "Quality of an [information system] reflecting the logical
      correctness and reliability of the operating system; the logical
      completeness of the hardware and software implementing the
      protection mechanisms; and the consistency of the data structures
      and occurrence of the stored data." [from an earlier version of
      C4009]

      Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
      it mixes several concepts in a potentially misleading way.
      Instead, IDOCs should use the term with definition 1 and,
      depending on what is meant, couple the term with additional, more
      specifically descriptive and informative terms, such as
      "correctness", "reliability", and "data integrity".

   $ system integrity service
      (I) A security service that protects system resources in a
      verifiable manner against unauthorized or accidental change, loss,
      or destruction. (See: system integrity.)

   $ system low
      (I) The lowest security level supported by a system at a
      particular time or in a particular environment. (Compare: system
      high.)

   $ system resource
      (I) Data contained in an information system; or a service provided
      by a system; or a system capacity, such as processing power or
      communication bandwidth; or an item of system equipment (i.e.,

      hardware, firmware, software, or documentation); or a facility
      that houses system operations and equipment. (See: system
      component.)

   $ system security officer (SSO)
      (I) A person responsible for enforcement or administration of the
      security policy that applies to a system. (Compare: manager,
      operator.)

   $ system user
      (I) A system entity that consumes a product or service provided by
      the system, or that accesses and employs system resources to
      produce a product or service of the system. (See: access, [R2504].
      Compare: authorized user, manager, operator, principal, privileged
      user, subject, subscriber, system entity, unauthorized user.)

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the term is used in many ways and could easily be
      misunderstood:
      -  This term usually refers to an entity that has been authorized
         to access the system, but the term sometimes is used without
         regard for whether access is authorized.
      -  This term usually refers to a living human being acting either
         personally or in an organizational role. However, the term also
         may refer to an automated process in the form of hardware,
         software, or firmware; to a set of persons; or to a set of
         processes.
      -  IDOCs SHOULD NOT use the term to refer to a mixed set
         containing both persons and processes. This exclusion is
         intended to prevent situations that might cause a security
         policy to be interpreted in two different and conflicting ways.

      A system user can be characterized as direct or indirect:
      -  "Passive user": A system entity that is (a) outside the
         system's security perimeter *and* (b) can receive output from
         the system but cannot provide input or otherwise interact with
         the system.
      -  "Active user": A system entity that is (a) inside the system's
         security perimeter *or* (b) can provide input or otherwise
         interact with the system.

   $ TACACS
      (I) See: Terminal Access Controller (TAC) Access Control System.

   $ TACACS+
      (I) A TCP-based protocol that improves on TACACS by separating the
      functions of authentication, authorization, and accounting and by
      encrypting all traffic between the network access server and

      authentication server. TACACS+ is extensible to allow any
      authentication mechanism to be used with TACACS+ clients.

   $ tamper
      (I) Make an unauthorized modification in a system that alters the
      system's functioning in a way that degrades the security services
      that the system was intended to provide. (See: QUADRANT. Compare:
      secondary definitions under "corruption" and "misuse".)

   $ tamper-evident
      (I) A characteristic of a system component that provides evidence
      that an attack has been attempted on that component or system.

      Usage: Usually involves physical evidence. (See: tamper.)

   $ tamper-resistant
      (I) A characteristic of a system component that provides passive
      protection against an attack. (See: tamper.)

      Usage: Usually involves physical means of protection.

   $ tampering
      (I) /threat action/ See: secondary definitions under "corruption"
      and "misuse".

   $ target of evaluation (TOE)
      (N) /Common Criteria/ An information technology product or system
      that is the subject of a security evaluation, together with the
      product's associated administrator and user documentation.
      (Compare: protection profile.)

      Tutorial: The security characteristics of the target of evaluation
      (TOE) are described in specific terms by a corresponding security
      target, or in more general terms by a protection profile. In
      Common Criteria philosophy, it is important that a TOE be
      evaluated against the specific set of criteria expressed in the
      target. This evaluation consists of rigorous analysis and testing
      performed by an accredited, independent laboratory. The scope of a
      TOE evaluation is set by the EAL and other requirements specified
      in the target. Part of this process is an evaluation of the target
      itself, to ensure that it is correct, complete, and internally
      consistent and can be used as the baseline for the TOE evaluation.

   $ TCB
      (N) See: trusted computing base.

   $ TCC field
      (I) See: Transmission Control Code field.

   $ TCG
      (N) See: Trusted Computing Group.

   $ TCP
      (I) See: Transmission Control Protocol.

   $ TCP/IP
      (I) Synonym for "Internet Protocol Suite".

   $ TCSEC
      (N) See: Trusted Computer System Evaluation Criteria. (Compare:
      TSEC.)

   $ TDEA
      (I) See: Triple Data Encryption Algorithm.

   $ teardrop attack
      (D) /slang/ A denial-of-service attack that sends improperly
      formed IP packet fragments with the intent of causing the
      destination system to fail.

      Deprecated Term: IDOCs that use this term SHOULD state a
      definition for it because the term is often used imprecisely and
      could easily be misunderstood. (See: Deprecated Usage under "Green
      Book".)

   $ technical non-repudiation
      (I) See: (secondary definition under) non-repudiation.

   $ technical security
      (I) Security mechanisms and procedures that are implemented in and
      executed by computer hardware, firmware, or software to provide
      automated protection for a system. (See: security architecture.
      Compare: administrative security.)

   $ Telecommunications Security Word System (TSEC)
      (O) /U.S. Government/ A terminology for designating
      telecommunication security equipment. (Compare: TCSEC.)

      Tutorial: A TSEC designator has the following parts:
      -  Prefix "TSEC/" for items and systems, or suffix "/TSEC" for
         assemblies. (Often omitted when the context is clear.)
      -  First letter, for function: "C" COMSEC equipment system, "G"
         general purpose, "K" cryptographic, "H" crypto-ancillary, "M"
         manufacturing, "N" noncryptographic, "S" special purpose.
      -  Second letter, for type or purpose: "G" key generation, "I"
         data transmission, "L" literal conversion, "N" signal
         conversion, "O" multipurpose, "P" materials production, "S"

         special purpose, "T" testing or checking, "U" television, "W"
         teletypewriter, "X" facsimile, "Y" speech.
      -  Optional third letter, used only in designations of assemblies,
         for type or purpose: "A" advancing, "B" base or cabinet, "C"
         combining, "D" drawer or panel, "E" strip or chassis, "F" frame
         or rack, "G" key generator, "H" keyboard, "I" translator or
         reader, "J" speech processing, "K" keying or permuting, "L"
         repeater, "M" memory or storage, "O" observation, "P" power
         supply or converter, "R" receiver, "S" synchronizing, "T"
         transmitter, "U" printer, "V" removable COMSEC component, "W"
         logic programmer/programming, "X" special purpose.
      -  Model number, usually two or three digits, assigned
         sequentially within each letter combination (e.g., KG-34, KG-
         84).
      -  Optional suffix letter, used to designate a version. First
         version has no letter, next version has "A" (e.g., KG-84, KG-
         84A), etc.

   $ TELNET
      (I) A TCP-based, Application-Layer, Internet Standard protocol
      (RFC 854) for remote login from one host to another.

   $ TEMPEST
      1. (N) Short name for technology and methods for protecting
      against data compromise due to electromagnetic emanations from
      electrical and electronic equipment. [Army, Russ] (See:
      inspectable space, soft TEMPEST, TEMPEST zone. Compare: QUADRANT)

      2. (O) /U.S. Government/ "Short name referring to investigation,
      study, and control of compromising emanations from IS equipment."
      [C4009]

      Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
      "electromagnetic emanations security"; instead, use EMSEC. Also,
      the term is NOT an acronym for Transient Electromagnetic Pulse
      Surveillance Technology.

      Tutorial: The U.S. Federal Government issues security policies
      that (a) state specifications and standards for techniques to
      reduce the strength of emanations from systems and reduce the
      ability of unauthorized parties to receive and make use of
      emanations and (b) state rules for applying those techniques.
      Other nations presumably do the same.

   $ TEMPEST zone
      (O) "Designated area [i.e., a physical volume] within a facility
      where equipment with appropriate TEMPEST characteristics ... may

      be operated." [C4009] (See: emanation security, TEMPEST. Compare:
      control zone, inspectable space.)

      Tutorial: The strength of an electromagnetic signal decreases in
      proportion to the square of the distance between the source and
      the receiver. Therefore, EMSEC for electromagnetic signals can be
      achieved by a combination of (a) reducing the strength of
      emanations to a defined level and (b) establishing around that
      equipment an appropriately sized physical buffer zone from which
      unauthorized entities are excluded. By making the zone large
      enough, it is possible to limit the signal strength available to
      entities outside the zone to a level lower than can be received
      and read with known, state-of-the-art methods. Typically, the need
      for and size of a TEMPEST zone established by a security policy
      depends not only on the measured level of signal emitted by
      equipment, but also on the perceived threat level in the
      equipment's environment.

   $ Terminal Access Controller (TAC) Access Control System (TACACS)
      (I) A UDP-based authentication and access control protocol [R1492]
      in which a network access server receives an identifier and
      password from a remote terminal and passes them to a separate
      authentication server for verification. (See: TACACS+.)

      Tutorial: TACACS can provide service not only for network access
      servers but also routers and other networked computing devices via
      one or more centralized authentication servers. TACACS was
      originally developed for ARPANET and has evolved for use in
      commercial equipment.

   $ TESS
      (I) See: The Exponential Encryption System.

   $ The Exponential Encryption System (TESS)
      (I) A system of separate but cooperating cryptographic mechanisms
      and functions for the secure authenticated exchange of
      cryptographic keys, the generation of digital signatures, and the
      distribution of public keys. TESS uses asymmetric cryptography,
      based on discrete exponentiation, and a structure of self-
      certified public keys. [R1824]

   $ theft
      (I) /threat action/ See: secondary definitions under
      "interception" and "misappropriation".

   $ threat
      1a. (I) A potential for violation of security, which exists when
      there is an entity, circumstance, capability, action, or event

      that could cause harm. (See: dangling threat, INFOCON level,
      threat action, threat agent, threat consequence. Compare: attack,
      vulnerability.)

      1b. (N) Any circumstance or event with the potential to adversely
      affect a system through unauthorized access, destruction,
      disclosure, or modification of data, or denial of service. [C4009]
      (See: sensitive information.)

      Usage: (a) Frequently misused with the meaning of either "threat
      action" or "vulnerability". (b) In some contexts, "threat" is used
      more narrowly to refer only to intelligent threats; for example,
      see definition 2 below. (c) In some contexts, "threat" is used
      more broadly to cover both definition 1 and other concepts, such
      as in definition 3 below.

      Tutorial: A threat is a possible danger that might exploit a
      vulnerability. Thus, a threat may be intentional or not:
      -  "Intentional threat": A possibility of an attack by an
         intelligent entity (e.g., an individual cracker or a criminal
         organization).
      -  "Accidental threat": A possibility of human error or omission,
         unintended equipment malfunction, or natural disaster (e.g.,
         fire, flood, earthquake, windstorm, and other causes listed in
         [FP031]).

      The Common Criteria characterizes a threat in terms of (a) a
      threat agent, (b) a presumed method of attack, (c) any
      vulnerabilities that are the foundation for the attack, and (d)
      the system resource that is attacked. That characterization agrees
      with the definitions in this Glossary (see: diagram under
      "attack").

      2. (O) The technical and operational ability of a hostile entity
      to detect, exploit, or subvert a friendly system and the
      demonstrated, presumed, or inferred intent of that entity to
      conduct such activity.

      Tutorial: To be likely to launch an attack, an adversary must have
      (a) a motive to attack, (b) a method or technical ability to make
      the attack, and (c) an opportunity to appropriately access the
      targeted system.

      3. (D) "An indication of an impending undesirable event." [Park]

      Deprecated Definition: IDOCs SHOULD NOT use this term with
      definition 3 because the definition is ambiguous; the definition
      was intended to include the following three meanings:

      -  "Potential threat": A possible security violation; i.e., the
         same as definition 1.
      -  "Active threat": An expression of intent to violate security.
         (Context usually distinguishes this meaning from the previous
         one.)
      -  "Accomplished threat" or "actualized threat": That is, a threat
         action. Deprecated Usage: IDOCs SHOULD NOT use the term
         "threat" with this meaning; instead, use "threat action".

   $ threat action
      (I) A realization of a threat, i.e., an occurrence in which system
      security is assaulted as the result of either an accidental event
      or an intentional act. (See: attack, threat, threat consequence.)

      Tutorial: A complete security architecture deals with both
      intentional acts (i.e., attacks) and accidental events [FP031].
      (See: various kinds of threat actions defined under the four kinds
      of "threat consequence".)

   $ threat agent
      (I) A system entity that performs a threat action, or an event
      that results in a threat action.

   $ threat analysis
      (I) An analysis of the threat actions that might affect a system,
      primarily emphasizing their probability of occurrence but also
      considering their resulting threat consequences. Example: RFC
      3833. (Compare: risk analysis.)

   $ threat consequence
      (I) A security violation that results from a threat action.

      Tutorial: The four basic types of threat consequence are
      "unauthorized disclosure", "deception", "disruption", and
      "usurpation". (See main Glossary entries of each of these four
      terms for lists of the types of threat actions that can result in
      these consequences.)

   $ thumbprint
      1. (I) A pattern of curves formed by the ridges on the tip of a
      thumb. (See: biometric authentication, fingerprint.)

      2. (D) Synonym for some type of "hash result". (See: biometric
      authentication. Compare: fingerprint.)

      Deprecated Usage: IDOCs SHOULD NOT use this term with definition 2
      because that meaning mixes concepts in a potentially misleading
      way.

   $ ticket
      (I) Synonym for "capability token".

      Tutorial: A ticket is usually granted by a centralized access
      control server (ticket-granting agent) to authorize access to a
      system resource for a limited time. Tickets can be implemented
      with either symmetric cryptography (see: Kerberos) or asymmetric
      cryptography (see: attribute certificate).

   $ tiger team
      (O) A group of evaluators employed by a system's managers to
      perform penetration tests on the system.

      Deprecated Usage: It is likely that other cultures use different
      metaphors for this concept. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
      Usage under "Green Book".)

   $ time stamp
      1. (I) /noun/ With respect to a data object, a label or marking in
      which is recorded the time (time of day or other instant of
      elapsed time) at which the label or marking was affixed to the
      data object. (See: Time-Stamp Protocol.)

      2. (O) /noun/ "With respect to a recorded network event, a data
      field in which is recorded the time (time of day or other instant
      of elapsed time) at which the event took place." [A1523]

      Tutorial: A time stamp can be used as evidence to prove that a
      data object existed (or that an event occurred) at or before a
      particular time. For example, a time stamp might be used to prove
      that a digital signature based on a private key was created while
      the corresponding public-key certificate was valid, i.e., before
      the certificate either expired or was revoked. Establishing this
      proof would enable the certificate to be used after its expiration
      or revocation, to verify a signature that was created earlier.
      This kind of proof is required as part of implementing PKI
      services, such as non-repudiation service, and long-term security
      services, such as audit.

   $ Time-Stamp Protocol
      (I) An Internet protocol (RFC 3161) that specifies how a client
      requests and receives a time stamp from a server for a data object
      held by the client.

      Tutorial: The protocol describes the format of (a) a request sent
      to a time-stamp authority and (b) the response that is returned
      containing a time stamp. The authority creates the stamp by

      concatenating (a) a hash value of the input data object with (b) a
      UTC time value and other parameters (policy OID, serial number,
      indication of time accuracy, nonce, DN of the authority, and
      various extensions), and then signing that dataset with the
      authority's private key as specified in CMS. Such an authority
      typically would operate as a trusted third-party service, but
      other operational models might be used.

   $ timing channel
      (I) See: covert timing channel.

   $ TKEY
      (I) A mnemonic referring to an Internet protocol (RFC 2930) for
      establishing a shared secret key between a DNS resolver and a DNS
      name server. (See: TSIG.)

   $ TLS
      (I) See: Transport Layer Security.

   $ TLSP
      (N) See: Transport Layer Security Protocol.

   $ TOE
      (N) See: target of evaluation.

   $ token
      1. (I) /cryptography/ See: cryptographic token. (Compare: dongle.)

      2. (I) /access control/ An object that is used to control access
      and is passed between cooperating entities in a protocol that
      synchronizes use of a shared resource. Usually, the entity that
      currently holds the token has exclusive access to the resource.
      (See: capability token.)

      Usage: This term is heavily overloaded in the computing
      literature; therefore, IDOCs SHOULD NOT use this term with any
      definition other than 1 or 2.

      3a. (D) /authentication/ A data object or a physical device used
      to verify an identity in an authentication process.

      3b. (D) /U.S. Government/ Something that the claimant in an
      authentication process (i.e., the entity that claims an identity)
      possesses and controls, and uses to prove the claim during the
      verification step of the process. [SP63]

      Deprecated usage: IDOCs SHOULD NOT use this term with definitions
      3a and 3b; instead, use more specifically descriptive and

      informative terms such as "authentication information" or
      "cryptographic token", depending on what is meant.

      NIST defines four types of claimant tokens for electronic
      authentication in an information system [SP63]. IDOCs SHOULD NOT
      use these four NIST terms; they mix concepts in potentially
      confusing ways and duplicate the meaning of better-established
      terms. These four terms can be avoided by using more specifically
      descriptive terms as follows:
      -  NIST "hard token": A hardware device that contains a protected
         cryptographic key. (This is a type of "cryptographic token",
         and the key is a type of "authentication information".)
      -  NIST "one-time password device token": A personal hardware
         device that generates one-time passwords. (One-time passwords
         are typically generated cryptographically. Therefore, this is a
         type of "cryptographic token", and the key is a type of
         "authentication information".)
      -  NIST "soft token": A cryptographic key that typically is stored
         on disk or some other magnetic media. (The key is a type of
         "authentication information"; "authentication key" would be a
         better description.)
      -  NIST "password token": A secret data value that the claimant
         memorizes. (This is a "password" that is being used as
         "authentication information".)

   $ token backup
      (I) A token management operation that stores sufficient
      information in a database (e.g., in a CAW) to recreate or restore
      a security token (e.g., a smart card) if it is lost or damaged.

   $ token copy
      (I) A token management operation that copies all the personality
      information from one security token to another. However, unlike in
      a token restore operation, the second token is initialized with
      its own, different local security values such as PINs and storage
      keys.

   $ token management
      (I) The process that includes initializing security tokens (e.g.,
      "smart card"), loading data into the tokens, and controlling the
      tokens during their lifecycle. May include performing key
      management and certificate management functions; generating and
      installing PINs; loading user personality data; performing card
      backup, card copy, and card restore operations; and updating
      firmware.

   $ token restore
      (I) A token management operation that loads a security token with
      data for the purpose of recreating (duplicating) the contents
      previously held by that or another token. (See: recovery.)

   $ token storage key
      (I) A cryptographic key used to protect data that is stored on a
      security token.

   $ top CA
      (I) Synonym for "root" in a certification hierarchy. (See: apex
      trust anchor.)

   $ top-level specification
      (I) "A non-procedural description of system behavior at the most
      abstract level; typically a functional specification that omits
      all implementation details." [NCS04] (See: formal top-level
      specification, Tutorial under "security policy".)

      Tutorial: A top-level specification is at a level of abstraction
      below "security model" and above "security architecture" (see:
      Tutorial under "security policy").

      A top-level specification may be descriptive or formal:
      -  "Descriptive top-level specification": One that is written in a
         natural language like English or an informal design notation.
      -  "Formal top-level specification": One that is written in a
         formal mathematical language to enable theorems to be proven
         that show that the specification correctly implements a set of
         formal requirements or a formal security model. (See:
         correctness proof.)

   $ TPM
      (N) See: Trusted Platform Module.

   $ traceback
      (I) Identification of the source of a data packet. (See:
      masquerade, network weaving.)

   $ tracker
      (N) An attack technique for achieving unauthorized disclosure from
      a statistical database. [Denns] (See: Tutorial under "inference
      control".)

   $ traffic analysis
      1. (I) Gaining knowledge of information by inference from
      observable characteristics of a data flow, even if the information
      is not directly available (e.g., when the data is encrypted).

      These characteristics include the identities and locations of the
      source(s) and destination(s) of the flow, and the flow's presence,
      amount, frequency, and duration of occurrence. The object of the
      analysis might be information in SDUs, information in the PCI, or
      both. (See: inference, traffic-flow confidentiality, wiretapping.
      Compare: signal analysis.)

      2. (O) "The inference of information from observation of traffic
      flows (presence, absence, amount, direction, and frequency)."
      [I7498-2]

   $ traffic-flow analysis
      (I) Synonym for "traffic analysis".

   $ traffic-flow confidentiality (TFC)
      1. (I) A data confidentiality service to protect against traffic
      analysis. (See: communications cover.)

      2. (O) "A confidentiality service to protect against traffic
      analysis." [I7498-2]

      Tutorial: Confidentiality concerns involve both direct and
      indirect disclosure of data, and the latter includes traffic
      analysis. However, operational considerations can make TFC
      difficult to achieve. For example, if Alice sends a product idea
      to Bob in an email message, she wants data confidentiality for the
      message's content, and she might also want to conceal the
      destination of the message to hide Bob's identity from her
      competitors. However, the identity of the intended recipient, or
      at least a network address for that recipient, needs to be made
      available to the mail system. Thus, complex forwarding schemes may
      be needed to conceal the ultimate destination as the message
      travels through the open Internet (see: onion routing).

      Later, if Alice uses an ATM during a clandestine visit to
      negotiate with Bob, she might prefer that her bank conceal the
      origin of her transaction, because knowledge of the ATM's location
      might allow a competitor to infer Bob's identity. The bank, on the
      other hand, might prefer to protect only Alice's PIN (see:
      selective-field confidentiality).

      A TFC service can be either full or partial:
      -  "Full TFC": This type of service conceals all traffic
         characteristics.
      -  "Partial TFC": This type of service either (a) conceals some
         but not all of the characteristics or (b) does not completely
         conceal some characteristic.

      On point-to-point data links, full TFC can be provided by
      enciphering all PDUs and also generating a continuous, random data
      stream to seamlessly fill all gaps between PDUs. To a wiretapper,
      the link then appears to be carrying an unbroken stream of
      enciphered data. In other cases -- including on a shared or
      broadcast medium, or end-to-end in a network -- only partial TFC
      is possible, and that may require a combination of techniques. For
      example, a LAN that uses "carrier sense multiple access with
      collision detection" (CSMA/CD; a.k.a. "listen while talk") to
      control access to the medium, relies on detecting intervals of
      silence, which prevents using full TFC. Partial TFC can be
      provided on that LAN by measures such as adding spurious PDUs,
      padding PDUs to a constant size, or enciphering addresses just
      above the Physical Layer; but these measures reduce the efficiency
      with which the LAN can carry traffic. At higher protocol layers,
      SDUs can be protected, but addresses and other items of PCI must
      be visible at the layers below.

   $ traffic key
      (I) A cryptographic key used by a device for protecting
      information that is being transmitted between devices, as opposed
      to protecting information that being is maintained in the device.
      (Compare: storage key.)

   $ traffic padding
      (I) "The generation of spurious instances of communication,
      spurious data units, and/or spurious data within data units."
      [I7498-2]

   $ tranquility property
      (N) /formal model/ Property of a system whereby the security level
      of an object cannot change while the object is being processed by
      the system. (See: Bell-LaPadula model.)

   $ transaction
      1. (I) A unit of interaction between an external entity and a
      system, or between components within a system, that involves a
      series of system actions or events.

      2. (O) "A discrete event between user and systems that supports a
      business or programmatic purpose." [M0404]

      Tutorial: To maintain secure state, transactions need to be
      processed coherently and reliably. Usually, they need to be
      designed to be atomic, consistent, isolated, and durable [Gray]:
      -  "Atomic": All actions and events that comprise the transaction
         are guaranteed to be completed successfully, or else the result
         is as if none at all were executed.

      -  "Consistent": The transaction satisfies correctness constraints
         defined for the data that is being processed.
      -  "Isolated": If two transactions are performed concurrently,
         they do not interfere with each other, and it appears as though
         the system performs one at a time.
      -  "Durable": System state and transaction semantics survive
         system failures.

   $ TRANSEC
      (I) See: transmission security.

   $ Transmission Control Code field (TCC field)
      (I) A data field that provides a means to segregate traffic and
      define controlled communities of interest in the security option
      (option type = 130) of IPv4's datagram header format. The TCC
      values are alphanumeric trigraphs assigned by the U.S. Government
      as specified in RFC 791.

   $ Transmission Control Protocol (TCP)
      (I) An Internet Standard, Transport-Layer protocol (RFC 793) that
      reliably delivers a sequence of datagrams from one computer to
      another in a computer network. (See: TCP/IP.)

      Tutorial: TCP is designed to fit into a layered suite of protocols
      that support internetwork applications. TCP assumes it can obtain
      a simple but potentially unreliable end-to-end datagram service
      (such as IP) from the lower-layer protocols.

   $ transmission security (TRANSEC)
      (I) COMSEC measures that protect communications from interception
      and exploitation by means other than cryptanalysis. Example:
      frequency hopping. (Compare: anti-jam, traffic flow
      confidentiality.)

   $ Transport Layer
      See: Internet Protocol Suite, OSIRM.

   $ Transport Layer Security (TLS)
      (I) TLS is an Internet protocol [R4346] that is based on, and very
      similar to, SSL Version 3.0. (Compare: TLSP.)

      Tutorial: The TLS protocol is misnamed. The name misleadingly
      suggests that TLS is situated in the IPS Transport Layer, but TLS
      is always layered above a reliable Transport-Layer protocol
      (usually TCP) and either layered immediately below or integrated
      with an Application-Layer protocol (often HTTP).

   $ Transport Layer Security Protocol (TLSP)
      (N) An end-to-end encryption protocol (ISO 10736) that provides
      security services at the bottom of OSIRM Layer 4, i.e., directly
      above Layer 3. (Compare: TLS.)

      Tutorial: TLSP evolved directly from SP4.

   $ transport mode
      (I) One of two ways to apply AH or ESP to protect data packets; in
      this mode, the IPsec protocol encapsulates (i.e., the protection
      applies to) the packets of an IPS Transport-Layer protocol (e.g.,
      TCP, UDP), which normally is carried directly above IP in an IPS
      protocol stack. (Compare: tunnel mode.)

      Tutorial: An IPsec transport-mode security association is always
      between two hosts; neither end has the role of a security gateway.
      Whenever either end of an IPsec security association is a security
      gateway, the association is required to be in tunnel mode.

   $ transposition
      (I) /cryptography/ A method of encryption in which elements of the
      plain text retain their original form but undergo some change in
      their sequential position. (Compare: substitution.)

   $ trap door
      (I) Synonym for "back door".

   $ trespass
      (I) /threat action/ See: secondary definition under "intrusion".

   $ Triple Data Encryption Algorithm
      (I) A block cipher that transforms each 64-bit plaintext block by
      applying the DEA three successive times, using either two or three
      different keys for an effective key length of 112 or 168 bits.
      [A9052, SP67]

      Example: A variation proposed for IPsec's ESP uses a 168-bit key,
      consisting of three independent 56-bit values used by the DEA, and
      a 64-bit initialization vector. Each datagram contains an IV to
      ensure that each received datagram can be decrypted even when
      other datagrams are dropped or a sequence of datagrams is
      reordered in transit. [R1851]

   $ triple-wrapped
      (I) /S-MIME/ Data that has been signed with a digital signature,
      then encrypted, and then signed again. [R2634]

   $ Trojan horse
      (I) A computer program that appears to have a useful function, but
      also has a hidden and potentially malicious function that evades
      security mechanisms, sometimes by exploiting legitimate
      authorizations of a system entity that invokes the program. (See:
      malware, spyware. Compare: logic bomb, virus, worm.)

   $ trust
      1. (I) /information system/ A feeling of certainty (sometimes
      based on inconclusive evidence) either (a) that the system will
      not fail or (b) that the system meets its specifications (i.e.,
      the system does what it claims to do and does not perform unwanted
      functions). (See: trust level, trusted system, trustworthy system.
      Compare: assurance.)

      Tutorial: Components of a system can be grouped into three classes
      of trust [Gass]:
      -  "Trusted": The component is responsible for enforcing security
         policy on other components; the system's security depends on
         flawless operation of the component. (See: trusted process.)
      -  "Benign": The component is not responsible for enforcing
         security policy, but it has sensitive authorizations. It must
         be trusted not to intentionally violate security policy, but
         security violations are assumed to be accidental and not likely
         to affect overall system security.
      -  "Untrusted": The component is of unknown or suspicious
         provenance and must be treated as deliberately malicious. (See:
         malicious logic.)

      2. (I) /PKI/ A relationship between a certificate user and a CA in
      which the user acts according to the assumption that the CA
      creates only valid digital certificates.

      Tutorial: "Generally, an entity is said to 'trust' a second entity
      when the first entity makes the assumption that the second entity
      will behave exactly as the first entity expects. This trust may
      apply only for some specific function. The key role of trust in
      [X.509] is to describe the relationship between an entity [i.e., a
      certificate user] and a [CA]; an entity shall be certain that it
      can trust the CA to create only valid and reliable certificates."
      [X509]

   $ trust anchor
      (I) /PKI/ An established point of trust (usually based on the
      authority of some person, office, or organization) from which a
      certificate user begins the validation of a certification path.
      (See: apex trust anchor, path validation, trust anchor CA, trust
      anchor certificate, trust anchor key.)

      Usage: IDOCs that use this term SHOULD state a definition for it
      because it is used in various ways in existing IDOCs and other PKI
      literature. The literature almost always uses this term in a sense
      that is equivalent to this definition, but usage often differs
      with regard to what constitutes the point of trust.

      Tutorial: A trust anchor may be defined as being based on a public
      key, a CA, a public-key certificate, or some combination or
      variation of those:

      -  1. A public key as a point of trust: Although a certification
         path is defined as beginning with a "sequence of public-key
         certificates", an implementation of a path validation process
         might not explicitly handle a root certificate as part of the
         path, but instead begin the process by using a trusted root key
         to verify the signature on a certificate that was issued by the
         root.

         Therefore, "trust anchor" is sometimes defined as just a public
         key. (See: root key, trust anchor key, trusted key.)

      -  2. A CA as a point of trust: A trusted public key is just one
         of the data elements needed for path validation; the IPS path
         validation algorithm [R3280] also needs the name of the CA to
         which that key belongs, i.e., the DN of the issuer of the first
         X.509 certificate to be validated on the path. (See: issue.)

         Therefore, "trust anchor" is sometimes defined as either just a
         CA (where some public key is implied) or as a CA together with
         a specified public key belonging to that CA. (See: root, trust
         anchor CA, trusted CA.)

         Example: "A public key and the name of a [CA] that is used to
         validate the first certificate in a sequence of certificates.
         The trust anchor public key is used to verify the signature on
         a certificate issued by a trust anchor [CA]." [SP57]

      -  3. A public-key certificate as a point of trust: Besides the
         trusted CA's public key and name, the path validation algorithm
         needs to know the digital signature algorithm and any
         associated parameters with which the public key is used, and
         also any constraints that have been placed on the set of paths
         that may be validated using the key. All of this information is
         available from a CA's public-key certificate.

         Therefore, "trust anchor" is sometimes defined as a public-key
         certificate of a CA. (See: root certificate, trust anchor
         certificate, trusted certificate.)

      -  4. Combinations: Combinations and variations of the first three
         definitions are also used in the PKI literature.

         Example: "trust anchor information". The IPS standard for path
         validation [R3280] specifies the information that describes "a
         CA that serves as a trust anchor for the certification path.
         The trust anchor information includes: (a) the trusted issuer
         name, (b) the trusted public key algorithm, (c) the trusted
         public key, and (d) optionally, the trusted public key
         parameters associated with the public key. The trust anchor
         information may be provided to the path processing procedure in
         the form of a self-signed certificate. The trusted anchor
         information is trusted because it was delivered to the path
         processing procedure by some trustworthy out-of-band procedure.
         If the trusted public key algorithm requires parameters, then
         the parameters are provided along with the trusted public key."

   $ trust anchor CA
      (I) A CA that is the subject of a trust anchor certificate or
      otherwise establishes a trust anchor key. (See: root, trusted CA.)

      Tutorial: The selection of a CA to be a trust anchor is a matter
      of policy. Some of the possible choices include (a) the top CA in
      a hierarchical PKI, (b) the CA that issued the verifier's own
      certificate, or (c) any other CA in a network PKI. Different
      applications may rely on different trust anchors, or may accept
      paths that begin with any of a set of trust anchors. The IPS path
      validation algorithm is the same, regardless of the choice.

   $ trust anchor certificate
      (I) A public-key certificate that is used to provide the first
      public key in a certification path. (See: root certificate, trust
      anchor, trusted certificate.)

   $ trust anchor key
      (I) A public key that is used as the first public key in a
      certification path. (See: root key, trust anchor, trusted public
      key.)

   $ trust anchor information
      (I) See: secondary definition under "trust anchor".

   $ trust chain
      (D) Synonym for "certification path". (See: trust anchor, trusted
      certificate.)

      Deprecated Term: IDOCs SHOULD NOT use this term, because it
      unnecessarily duplicates the meaning of the internationally
      standardized term.

      Also, the term mixes concepts in a potentially misleading way.
      Having "trust" involves factors unrelated to simply verifying
      signatures and performing other tests as specified by a standard
      algorithm for path validation (e.g., RFC 3280). Thus, even if a
      user is able to validate a certification path algorithmically, the
      user still might distrust one of the CAs that issued certificates
      in that path or distrust some other aspects of the PKI.

   $ trust-file PKI
      (I) A non-hierarchical PKI in which each certificate user has its
      own local file (which is used by application software) of trust
      anchors, i.e., either public keys or public-key certificates that
      the user trusts as starting points for certification paths. (See:
      trust anchor, web of trust. Compare: hierarchical PKI, mesh PKI.)

      Example: Popular browsers are distributed with an initial file of
      trust anchor certificates, which often are self-signed
      certificates. Users can add certificates to the file or delete
      from it. The file may be directly managed by the user, or the
      user's organization may manage it from a centralized server.

   $ trust hierarchy
      (D) Synonym for "certification hierarchy".

      Deprecated Usage: IDOCs SHOULD NOT use this term because it mixes
      concepts in a potentially misleading way, and because a trust
      hierarchy could be implemented in other ways. (See: trust, trust
      chain, web of trust.)

   $ trust level
      (N) A characterization of a standard of security protection to be
      met by an information system. (See: Common Criteria, TCSEC.)

      Tutorial: A trust level is based not only on (a) the presence of
      security mechanisms, but also on the use of (b) systems
      engineering discipline to properly structure the system and (c)
      implementation analysis to ensure that the system provides an
      appropriate degree of trust.

   $ trusted
      (I) See: secondary definition under "trust".

   $ trusted CA
      (I) A CA upon which a certificate user relies as issuing valid
      certificates; especially a CA that is used as a trust anchor CA.
      (See: certification path, root, trust anchor CA, validation.)

      Tutorial. This trust is transitive to the extent that the X.509
      certificate extensions permit; that is, if a trusted CA issues a
      certificate to another CA, a user that trusts the first CA also
      trusts the second CA if the user succeeds in validating the
      certificate path (see: path validation).

   $ trusted certificate
      (I) A digital certificate that a certificate user accepts as being
      valid "a priori", i.e., without testing the certificate to
      validate it as the final certificate on a certification path;
      especially a certificate that is used as a trust anchor
      certificate. (See: certification path, root certificate, trust
      anchor certificate, trust-file PKI, validation.)

      Tutorial: The acceptance of a certificate as trusted is a matter
      of policy and choice. Usually, a certificate is accepted as
      trusted because the user obtained it by reliable, out-of-band
      means that cause the user to believe the certificate accurately
      binds its subject's name to the subject's public key or other
      attribute values. Many choices are possible; e.g., a trusted
      public-key certificate might be (a) the root certificate in a
      hierarchical PKI, (b) the certificate of the CA that issued the
      user's own certificate in a mesh PKI, or (c) a certificate
      provided with an application that uses a trust-file PKI.

   $ Trusted Computer System Evaluation Criteria (TCSEC)
      (N) A standard for evaluating the security provided by operating
      systems [CSC1, DoD1]. Known as the "Orange Book" because of the
      color of its cover; first document in the Rainbow Series. (See:
      Common Criteria, Deprecated Usage under "Green Book", Orange Book,
      trust level, trusted system. Compare: TSEC.)

      Tutorial: The TCSEC defines classes of hierarchically ordered
      assurance levels for rating computer systems. From highest to
      lowest, the classes are as follows:
      -  Division A:  Verified protection.
           Beyond A1    Beyond current technology. (See: beyond A1.)
           Class  A1    Verified design. (See: SCOMP.)
      -  Division B:  Mandatory protection.
           Class  B3    Security domains.
           Class  B2    Structured protection. (See: Multics.)
           Class  B1    Labeled security protection.

      -  Division C:  Discretionary protection.
           Class  C2    Controlled access protection.
           Class  C1    Discretionary security protection.
      -  Division D:  Minimal protection, i.e., has been evaluated but
         does not meet the requirements for a higher evaluation class.

   $ trusted computing base (TCB)
      (N) "The totality of protection mechanisms within a computer
      system, including hardware, firmware, and software, the
      combination of which is responsible for enforcing a security
      policy." [NCS04] (See: "trusted" under "trust". Compare: TPM.)

   $ Trusted Computing Group (TCG)
      (N) A not-for-profit, industry standards organization formed to
      develop, define, and promote open standards for hardware-enabled
      trusted computing and security technologies, including hardware
      building blocks and software interfaces, across multiple
      platforms, peripherals, and devices. (See: TPM, trusted system.
      Compare: TSIG.)

   $ trusted distribution
      (I) /COMPUSEC/ "A trusted method for distributing the TCB
      hardware, software, and firmware components, both originals and
      updates, that provides methods for protecting the TCB from
      modification during distribution and for detection of any changes
      to the TCB that may occur." [NCS04] (See: code signing,
      configuration control.)

   $ trusted key
      (D) Abbreviation for "trusted public key" and also for other types
      of keys. (See: root key, trust anchor key.)

      Deprecated Usage: IDOCs SHOULD either (a) state a definition for
      this term or (b) use a different, less ambiguous term. This term
      is ambiguous when it stands alone; e.g., it could refer to a
      trusted public key or to a private key or symmetric key that is
      believed to be secure (i.e., not compromised).

   $ trusted path
      1a. (I) /COMPUSEC/ A mechanism by which a computer system user can
      communicate directly and reliably with the TCB and that can only
      be activated by the user or the TCB and cannot be imitated by
      untrusted software within the computer. [NCS04]

      1b. (I) /COMSEC/ A mechanism by which a person or process can
      communicate directly with a cryptographic module and that can only
      be activated by the person, process, or module, and cannot be
      imitated by untrusted software within the module. [FP140]

   $ Trusted Platform Module (TPM)
      (N) The name of a specification, published by the TCG, for a
      microcontroller that can store secured information; and also the
      general name of implementations of that specification. (Compare:
      TCB.)

   $ trusted process
      (I) A system component that has privileges that enable it to
      affect the state of system security and that can, therefore,
      through incorrect or malicious execution, violate the system's
      security policy. (See: privileged process, trusted system.)

   $ trusted public key
      (I) A public key upon which a user relies; especially a public key
      that is used as a trust anchor key. (See: certification path, root
      key, trust anchor key, validation.)

      Tutorial: A trusted public key could be (a) the root key in a
      hierarchical PKI, (b) the key of the CA that issued the user's own
      certificate in a mesh PKI, or (c) any key accepted by the user in
      a trust-file PKI.

   $ trusted recovery
      (I) A process that, after a system has experienced a failure or an
      attack, restores the system to normal operation (or to a secure
      state) without causing a security compromise. (See: recovery.)

   $ trusted subnetwork
      (I) A subnetwork containing hosts and routers that trust each
      other not to engage in active or passive attacks. (There also is
      an assumption that the underlying communication channels, such as
      telephone lines or a LAN, are protected from attack.)

   $ trusted system
      1. (I) /information system/ A system that operates as expected,
      according to design and policy, doing what is required -- despite
      environmental disruption, human user and operator errors, and
      attacks by hostile parties -- and not doing other things [NRC98].
      (See: trust level, trusted process. Compare: trustworthy.)

      2. (N) /multilevel secure/ "A [trusted system is a] system that
      employs sufficient hardware and software assurance measures to
      allow its use for simultaneous processing of a range of sensitive
      or classified information." [NCS04] (See: multilevel security
      mode.)

   $ Trusted Systems Interoperability Group (TSIG)
      (N) A forum of computer vendors, system integrators, and users
      devoted to promoting interoperability of trusted computer systems.
      (See: trusted system. Compare: TCG.)

   $ trustworthy system
      1. (I) A system that not only is trusted, but also warrants that
      trust because the system's behavior can be validated in some
      convincing way, such as through formal analysis or code review.
      (See: trust. Compare: trusted.)

      2. (O) /Digital Signature Guidelines/ "Computer hardware,
      software, and procedures that: (a) are reasonably secure from
      intrusion and misuse; (b) provide a reasonably reliable level of
      availability, reliability, and correct operation; (c) are
      reasonably suited to performing their intended functions; and (d)
      adhere to generally accepted security principles." [DSG]

   $ TSEC
      (O) See: Telecommunications Security Nomenclature System.
      (Compare: TCSEC.)

   $ TSIG
      1. (N) See: Trusted System Interoperability Group.

      2. (I) A mnemonic (presumed to be derived from "Transaction
      SIGnature") referring to an Internet protocol (RFC 2845) for data
      origin authentication and data integrity for certain DNS
      operations. (See: TKEY.)

   $ tunnel
      1. (I) A communication channel created in a computer network by
      encapsulating (i.e., layering) a communication protocol's data
      packets in (i.e., above) a second protocol that normally would be
      carried above, or at the same layer as, the first one. (See: L2TP,
      tunnel mode, VPN. Compare: covert channel.)

      Tutorial: Tunneling can involve almost any two IPS protocol
      layers. For example, a TCP connection between two hosts could
      conceivably be carried above SMTP (i.e., in SMTP messages) as a
      covert channel to evade access controls that a security gateway
      applies to the normal TCP layer that is below SMTP.

      Usually, however, a tunnel is a logical point-to-point link --
      i.e., an OSIRM Layer 2 connection -- created by encapsulating the
      Layer 2 protocol in one of the following three types of IPS
      protocols: (a) an IPS Transport-Layer protocol (such as TCP), (b)
      an IPS Network-Layer or Internet-Layer protocol (such as IP), or

      (c) another Layer 2 protocol. In many cases, the encapsulation is
      accomplished with an extra, intermediate protocol (i.e., a
      "tunneling protocol"; e.g., L2TP) that is layered below the
      tunneled Layer 2 protocol and above the encapsulating protocol.

      Tunneling can be used to move data between computers that use a
      protocol not supported by the network connecting them. Tunneling
      also can enable a computer network to use the services of a second
      network as though the second network were a set of point-to-point
      links between the first network's nodes. (See: VPN.)

      2. (O) /SET/ The name of a SET private extension that indicates
      whether the CA or the payment gateway supports passing encrypted
      messages to the cardholder through the merchant. If so, the
      extension lists OIDs of symmetric encryption algorithms that are
      supported.

   $ tunnel mode
      (I) One of two ways to apply the IPsec protocols (AH and ESP) to
      protect data packets; in this mode, the IPsec protocol
      encapsulates (i.e., the protection applies to) IP packets, rather
      than the packets of higher-layer protocols. (See: tunnel. Compare:
      transport mode.)

      Tutorial: Each end of a tunnel-mode security association may be
      either a host or a security gateway. Whenever either end of an
      IPsec security association is a security gateway, the association
      is required to be in tunnel mode.

   $ two-person control
      (I) The close surveillance and control of a system, a process, or
      materials (especially with regard to cryptography) at all times by
      a minimum of two appropriately authorized persons, each capable of
      detecting incorrect and unauthorized procedures with respect to
      the tasks to be performed and each familiar with established
      security requirements. (See: dual control, no-lone zone.)

   $ Twofish
      (O) A symmetric, 128-bit block cipher with variable key length
      (128, 192, or 256 bits), developed by Counterpane Labs as a
      candidate for the AES. (See: Blowfish.)

   $ type 0 product
      (O) /cryptography, U.S. Government/ Classified cryptographic
      equipment endorsed by NSA for use (when appropriately keyed) in
      electronically distributing bulk keying material.

   $ type 1 key
      (O) /cryptography, U.S. Government/ "Generated and distributed
      under the auspices of NSA for use in a cryptographic device for
      the protection of classified and sensitive national security
      information." [C4009]

   $ type 1 product
      (O) /cryptography, U.S. Government/ "Cryptographic equipment,
      assembly or component classified or certified by NSA for
      encrypting and decrypting classified and sensitive national
      security information when appropriately keyed. Developed using
      established NSA business processes and containing NSA approved
      algorithms. Used to protect systems requiring the most stringent
      protection mechanisms." [C4009]

      Tutorial: The current definition of this term is less specific
      than an earlier version: "Classified or controlled cryptographic
      item endorsed by the NSA for securing classified and sensitive
      U.S. Government information, when appropriately keyed. The term
      refers only to products, and not to information, key, services, or
      controls. Type 1 products contain classified NSA algorithms. They
      are available to U.S. Government users, their contractors, and
      federally sponsored non-U.S. Government activities subject to
      export restrictions in accordance with International Traffic in
      Arms Regulation." [from an earlier version of C4009] (See: ITAR.)

   $ type 2 key
      (O) /cryptography, U.S. Government/ "Generated and distributed
      under the auspices of NSA for use in a cryptographic device for
      the protection of unclassified national security information."
      [C4009]

   $ type 2 product
      (O) /cryptography, U.S. Government/ "Cryptographic equipment,
      assembly, or component certified by NSA for encrypting or
      decrypting sensitive national security information when
      appropriately keyed. Developed using established NSA business
      processes and containing NSA approved algorithms. Used to protect
      systems requiring protection mechanisms exceeding best commercial
      practices including systems used for the protection of
      unclassified national security information." [C4009]

      Tutorial: The current definition of this term is less specific
      than an earlier version: "Unclassified cryptographic equipment,
      assembly, or component, endorsed by the NSA, for use in national
      security systems as defined in Title 40 U.S.C. Section 1452."
      [from an earlier version of C4009] (See: national security system.
      Compare: EUCI.)

   $ type 3 key
      (O) /cryptography, U.S. Government/ "Used in a cryptographic
      device for the protection of unclassified sensitive information,
      even if used in a Type 1 or Type 2 product." [C4009]

   $ type 3 product
      (O) /cryptography, U.S. Government/ "Unclassified cryptographic
      equipment, assembly, or component used, when appropriately keyed,
      for encrypting or decrypting unclassified sensitive U.S.
      Government or commercial information, and to protect systems
      requiring protection mechanisms consistent with standard
      commercial practices. Developed using established commercial
      standards and containing NIST approved cryptographic
      algorithms/modules or successfully evaluated by the National
      Information Assurance Partnership (NIAP)." [C4009]

   $ type 4 key
      (O) /cryptography, U.S. Government/ "Used by a cryptographic
      device in support of its Type 4 functionality; i.e., any provision
      of key that lacks U.S. Government endorsement or oversight."
      [C4009]

   $ type 4 product
      (O) /cryptography, U.S. Government/ "Unevaluated commercial
      cryptographic equipment, assemblies, or components that neither
      NSA nor NIST certify for any Government usage. These products are
      typically delivered as part of commercial offerings and are
      commensurate with the vendor's commercial practices. These
      products may contain either vendor proprietary algorithms,
      algorithms registered by NIST, or algorithms registered by NIST
      and published in a FIPS." [C4009]

   $ UDP
      (I) See: User Datagram Protocol.

   $ UDP flood
      (I) A denial-of-service attack that takes advantage of (a) one
      system's UDP test function that generates a series of characters
      for each packet it receives and (b) another system's UPD test
      function that echoes any character it receives; the attack
      connects (a) to (b) to cause a nonstop flow of data between the
      two systems. (See: flooding.)

   $ unauthorized disclosure
      (I) A circumstance or event whereby an entity gains access to
      information for which the entity is not authorized.

      Tutorial: This type of threat consequence can be caused by the
      following types of threat actions: exposure, interception,
      inference, and intrusion. Some methods of protecting against this
      consequence include access control, flow control, and inference
      control. (See: data confidentiality.)

   $ unauthorized user
      (I) /access control/ A system entity that accesses a system
      resource for which the entity has not received an authorization.
      (See: user. Compare: authorized user, insider, outsider.)

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the term is used in many ways and could easily be
      misunderstood.

   $ uncertainty
      (N) An information-theoretic measure (usually stated as a number
      of bits) of the minimum amount of plaintext information that needs
      to be recovered from cipher text to learn the entire plain text
      that was encrypted. [SP63] (See: entropy.)

   $ unclassified
      (I) Not classified. (Compare: FOUO.)

   $ unencrypted
      (I) Not encrypted.

   $ unforgeable
      (I) /cryptography/ The property of a cryptographic data structure
      (i.e., a data structure that is defined using one or more
      cryptographic functions, e.g., "digital certificate") that makes
      it computationally infeasible to construct (i.e., compute) an
      unauthorized but correct value of the structure without having
      knowledge of one of more keys.

      Tutorial: This definition is narrower than general English usage,
      where "unforgeable" means unable to be fraudulently created or
      duplicated. In that broader sense, anyone can forge a digital
      certificate containing any set of data items whatsoever by
      generating the to-be-signed certificate and signing it with any
      private key whatsoever. But for PKI purposes, the forged data
      structure is invalid if it is not signed with the true private key
      of the claimed issuer; thus, the forgery will be detected when a
      certificate user uses the true public key of the claimed issuer to
      verify the signature.

   $ uniform resource identifier (URI)
      (I) A type of formatted identifier (RFC 3986) that encapsulates
      the name of an Internet object, and labels it with an
      identification of the name space, thus producing a member of the
      universal set of names in registered name spaces and of addresses
      referring to registered protocols or name spaces.

      Example: HTML uses URIs to identify the target of hyperlinks.

      Usage: "A URI can be classified as a locator (see: URL), a name
      (see: URN), or both. ... Instances of URIs from any given scheme
      may have the characteristics of names or locators or both, often
      depending on the persistence and care in the assignment of
      identifiers by the naming authority, rather than on any quality of
      the scheme." IDOCs SHOULD "use the general term 'URI' rather than
      the more restrictive terms 'URL' and 'URN'." (RFC 3986)

   $ uniform resource locator (URL)
      (I) A URI that describes the access method and location of an
      information resource object on the Internet. (See: Usage under
      "URI". Compare: URN.)

      Tutorial: The term URL "refers to the subset of URIs that, besides
      identifying a resource, provide a means of locating the resource
      by describing its primary access mechanism (e.g., its network
      'location')." (RFC 3986)

      A URL provides explicit instructions on how to access the named
      object. For example,
      "ftp://bbnarchive.bbn.com/foo/bar/picture/cambridge.zip" is a URL.
      The part before the colon specifies the access scheme or protocol,
      and the part after the colon is interpreted according to that
      access method. Usually, two slashes after the colon indicate the
      host name of a server (written as a domain name). In an FTP or
      HTTP URL, the host name is followed by the path name of a file on
      the server. The last (optional) part of a URL may be either a
      fragment identifier that indicates a position in the file, or a
      query string.

   $ uniform resource name (URN)
      (I) A URI with the properties of a name. (See: Usage under "URI".
      Compare: URL.)

      Tutorial: The term URN "has been used historically to refer to
      both URIs under the "urn" scheme (RFC 2141), which are required to
      remain globally unique and persistent even when the resource
      ceases to exist or becomes unavailable, and to any other URI with
      the properties of a name." (RFC 3986)

   $ untrusted
      (I) See: secondary definition under "trust".

   $ untrusted process
      1. (I) A system component that is not able to affect the state of
      system security through incorrect or malicious operation. Example:
      A component that has its operations confined by a security kernel.
      (See: trusted process.)

      2. (I) A system component that (a) has not been evaluated or
      examined for adherence to a specified security policy and,
      therefore, (b) must be assumed to contain logic that might attempt
      to circumvent system security.

   $ UORA
      (O) See: user-PIN ORA.

   $ update
      See: "certificate update" and "key update".

   $ upgrade
      (I) /data security/ Increase the classification level of data
      without changing the information content of the data. (See:
      classify, downgrade, regrade.)

   $ URI
      (I) See: uniform resource identifier.

   $ URL
      (I) See: uniform resource locator.

   $ URN
      (I) See: uniform resource name.

   $ user
      See: system user.

      Usage: IDOCs that use this term SHOULD state a definition for it
      because the term is used in many ways and could easily be
      misunderstood.

   $ user authentication service
      (I) A security service that verifies the identity claimed by an
      entity that attempts to access the system. (See: authentication,
      user.)

   $ User Datagram Protocol (UDP)
      (I) An Internet Standard, Transport-Layer protocol (RFC 768) that
      delivers a sequence of datagrams from one computer to another in a
      computer network. (See: UPD flood.)

      Tutorial: UDP assumes that IP is the underlying protocol. UDP
      enables application programs to send transaction-oriented data to
      other programs with minimal protocol mechanism. UDP does not
      provide reliable delivery, flow control, sequencing, or other end-
      to-end service guarantees that TCP does.

   $ user identifier
      (I) See: identifier.

   $ user identity
      (I) See: identity.

   $ user PIN
      (O) /MISSI/ One of two PINs that control access to the functions
      and stored data of a FORTEZZA PC card. Knowledge of the user PIN
      enables a card user to perform the FORTEZZA functions that are
      intended for use by an end user. (See: PIN. Compare: SSO PIN.)

   $ user-PIN ORA (UORA)
      (O) /MISSI/ A MISSI organizational RA that operates in a mode in
      which the ORA performs only the subset of card management
      functions that are possible with knowledge of the user PIN for a
      FORTEZZA PC card. (See: no-PIN ORA, SSO-PIN ORA.)

   $ usurpation
      (I) A circumstance or event that results in control of system
      services or functions by an unauthorized entity. This type of
      threat consequence can be caused by the following types of threat
      actions: misappropriation, misuse. (See: access control.)

   $ UTCTime
      (N) The ASN.1 data type "UTCTime" contains a calendar date
      (YYMMDD) and a time to a precision of either one minute (HHMM) or
      one second (HHMMSS), where the time is either (a) Coordinated
      Universal Time or (b) the local time followed by an offset that
      enables Coordinated Universal Time to be calculated. (See:
      Coordinated Universal Time. Compare: GeneralizedTime.)

      Usage: If you care about centuries or millennia, you probably need
      to use the GeneralizedTime data type instead of UTCTime.

   $ v1 certificate
      (N) An abbreviation that ambiguously refers to either an "X.509
      public-key certificate in version 1 format" or an "X.509 attribute
      certificate in version 1 format".

      Deprecated Usage: IDOCs MAY use this term as an abbreviation of
      "version 1 X.509 public-key certificate", but only after using the
      full term at the first instance. Otherwise, the term is ambiguous,
      because X.509 specifies both v1 public-key certificates and v1
      attribute certificates. (See: X.509 attribute certificate, X.509
      public-key certificate.)

   $ v1 CRL
      (N) Abbreviation of "X.509 CRL in version 1 format".

      Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
      term at its first occurrence and define the abbreviation there.

   $ v2 certificate
      (N) Abbreviation of "X.509 public-key certificate in version 2
      format".

      Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
      term at its first occurrence and define the abbreviation there.

   $ v2 CRL
      (N) Abbreviation of "X.509 CRL in version 2 format".

      Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
      term at its first occurrence and define the abbreviation there.

   $ v3 certificate
      (N) Abbreviation of "X.509 public-key certificate in version 3
      format".

      Usage: IDOCs MAY use this abbreviation, but SHOULD use the full
      term at its first occurrence and define the abbreviation there.

   $ valid certificate
      1. (I) A digital certificate that can be validated successfully.
      (See: validate, verify.)

      2. (I) A digital certificate for which the binding of the data
      items can be trusted.

   $ valid signature
      (D) Synonym for "verified signature".

      Deprecated Term: IDOCs SHOULD NOT use this synonym. This Glossary
      recommends saying "validate the certificate" and "verify the
      signature"; therefore, it would be inconsistent to say that a
      signature is "valid". (See: validate, verify.)

   $ validate
      1. (I) Establish the soundness or correctness of a construct.
      Example: certificate validation. (See: validate vs. verify.)

      2. (I) To officially approve something, sometimes in relation to a
      standard. Example: NIST validates cryptographic modules for
      conformance with [FP140].

   $ validate vs. verify
      Usage: To ensure consistency and align with ordinary English
      usage, IDOCs SHOULD comply with the following two rules:
      -  Rule 1: Use "validate" when referring to a process intended to
         establish the soundness or correctness of a construct (e.g.,
         "certificate validation"). (See: validate.)
      -  Rule 2: Use "verify" when referring to a process intended to
         test or prove the truth or accuracy of a fact or value (e.g.,
         "authenticate"). (See: verify.)

      Tutorial: The Internet security community sometimes uses these two
      terms inconsistently, especially in a PKI context. Most often,
      however, we say "verify the signature" but say "validate the
      certificate". That is, we "verify" atomic truths but "validate"
      data structures, relationships, and systems that are composed of
      or depend on verified items. This usage has a basis in Latin:

      The word "valid" derives from a Latin word that means "strong".
      Thus, to validate means to check that a construct is sound. For
      example, a certificate user validates a public-key certificate to
      establish trust in the binding that the certificate asserts
      between an identity and a key. This can include checking various
      aspects of the certificate's construction, such as verifying the
      digital signature on the certificate by performing calculations,
      verifying that the current time is within the certificate's
      validity period, and validating a certification path involving
      additional certificates.

      The word "verify" derives from a Latin word that means "true".
      Thus, to verify means to check the truth of an assertion by
      examining evidence or performing tests. For example, to verify an
      identity, an authentication process examines identification
      information that is presented or generated. To validate a
      certificate, a certificate user verifies the digital signature on
      the certificate by performing calculations, verifies that the

      current time is within the certificate's validity period, and may
      need to validate a certification path involving additional
      certificates.

   $ validation
      (I) See: validate vs. verify.

   $ validity period
      (I) /PKI/ A data item in a digital certificate that specifies the
      time period for which the binding between data items (especially
      between the subject name and the public key value in a public-key
      certificate) is valid, except if the certificate appears on a CRL
      or the key appears on a CKL. (See: cryptoperiod, key lifetime.)

   $ value-added network (VAN)
      (I) A computer network or subnetwork (usually a commercial
      enterprise) that transmits, receives, and stores EDI transactions
      on behalf of its users.

      Tutorial: A VAN may also provide additional services, ranging from
      EDI format translation, to EDI-to-FAX conversion, to integrated
      business systems.

   $ VAN
      (I) See: value-added network.

   $ verification
      1. (I) /authentication/ The process of examining information to
      establish the truth of a claimed fact or value. (See: validate vs.
      verify, verify. Compare: authentication.)

      2. (N) /COMPUSEC/ The process of comparing two levels of system
      specification for proper correspondence, such as comparing a
      security model with a top-level specification, a top-level
      specification with source code, or source code with object code.
      [NCS04]

   $ verified design
      (O) See: TCSEC Class A1.

   $ verify
      (I) To test or prove the truth or accuracy of a fact or value.
      (See: validate vs. verify, verification. Compare: authenticate.)

   $ vet
      (I) /verb/ To examine or evaluate thoroughly. (Compare:
      authenticate, identity proofing, validate, verify.)

   $ violation
      See: security violation.

   $ virtual private network (VPN)
      (I) A restricted-use, logical (i.e., artificial or simulated)
      computer network that is constructed from the system resources of
      a relatively public, physical (i.e., real) network (e.g., the
      Internet), often by using encryption (located at hosts or
      gateways), and often by tunneling links of the virtual network
      across the real network. (See: tunnel.)

      Tutorial: A VPN is generally less expensive to build and operate
      than a dedicated real network, because the virtual network shares
      the cost of system resources with other users of the underlying
      real network. For example, if a corporation has LANs at several
      different sites, each connected to the Internet by a firewall, the
      corporation could create a VPN by using encrypted tunnels to
      connect from firewall to firewall across the Internet.

   $ virus
      (I) A self-replicating (and usually hidden) section of computer
      software (usually malicious logic) that propagates by infecting --
      i.e., inserting a copy of itself into and becoming part of --
      another program. A virus cannot run by itself; it requires that
      its host program be run to make the virus active.

   $ Visa Cash
      (O) A smartcard-based electronic money system that incorporates
      cryptography and can be used to make payments via the Internet.
      (See: IOTP.)

   $ volatile media
      (I) Storage media that require an external power supply to
      maintain stored information. (Compare: non-volatile media,
      permanent storage.)

   $ VPN
      (I) See: virtual private network.

   $ vulnerability
      (I) A flaw or weakness in a system's design, implementation, or
      operation and management that could be exploited to violate the
      system's security policy. (See: harden.)

      Tutorial: A system can have three types of vulnerabilities: (a)
      vulnerabilities in design or specification; (b) vulnerabilities in
      implementation; and (c) vulnerabilities in operation and
      management. Most systems have one or more vulnerabilities, but

      this does not mean that the systems are too flawed to use. Not
      every threat results in an attack, and not every attack succeeds.
      Success depends on the degree of vulnerability, the strength of
      attacks, and the effectiveness of any countermeasures in use. If
      the attacks needed to exploit a vulnerability are very difficult
      to carry out, then the vulnerability may be tolerable. If the
      perceived benefit to an attacker is small, then even an easily
      exploited vulnerability may be tolerable. However, if the attacks
      are well understood and easily made, and if the vulnerable system
      is employed by a wide range of users, then it is likely that there
      will be enough motivation for someone to launch an attack.

   $ W3
      (D) Synonym for WWW.

      Deprecated Abbreviation: This abbreviation could be confused with
      W3C; use "WWW" instead.

   $ W3C
      (N) See: World Wide Web Consortium.

   $ war dialer
      (I) /slang/ A computer program that automatically dials a series
      of telephone numbers to find lines connected to computer systems,
      and catalogs those numbers so that a cracker can try to break the
      systems.

      Deprecated Usage: IDOCs that use this term SHOULD state a
      definition for it because the term could confuse international
      readers.

   $ Wassenaar Arrangement
      (N) The Wassenaar Arrangement on Export Controls for Conventional
      Arms and Dual-Use Goods and Technologies is a global, multilateral
      agreement approved by 33 countries in July 1996 to contribute to
      regional and international security and stability, by promoting
      information exchange concerning, and greater responsibility in,
      transfers of arms and dual-use items, thus preventing
      destabilizing accumulations. (See: International Traffic in Arms
      Regulations.)

      Tutorial: The Arrangement began operations in September 1996 with
      headquarters in Vienna. The participating countries were
      Argentina, Australia, Austria, Belgium, Bulgaria, Canada, Czech
      Republic, Denmark, Finland, France, Germany, Greece, Hungary,
      Ireland, Italy, Japan, Luxembourg, Netherlands, New Zealand,
      Norway, Poland, Portugal, Republic of Korea, Romania, Russian

      Federation, Slovak Republic, Spain, Sweden, Switzerland, Turkey,
      Ukraine, United Kingdom, and United States.

      Participating countries seek through their national policies to
      ensure that transfers do not contribute to the development or
      enhancement of military capabilities that undermine the goals of
      the arrangement, and are not diverted to support such
      capabilities. The countries maintain effective export controls for
      items on the agreed lists, which are reviewed periodically to
      account for technological developments and experience gained.
      Through transparency and exchange of views and information,
      suppliers of arms and dual-use items can develop common
      understandings of the risks associated with their transfer and
      assess the scope for coordinating national control policies to
      combat these risks. Members provide semi-annual notification of
      arms transfers, covering seven categories derived from the UN
      Register of Conventional Arms. Members also report transfers or
      denials of transfers of certain controlled dual-use items.
      However, the decision to transfer or deny transfer of any item is
      the sole responsibility of each participating country. All
      measures undertaken with respect to the arrangement are in
      accordance with national legislation and policies and are
      implemented on the basis of national discretion.

   $ watermarking
      See: digital watermarking.

   $ weak key
      (I) In the context of a particular cryptographic algorithm, a key
      value that provides poor security. (See: strong.)

      Example: The DEA has four "weak keys" [Schn] for which encryption
      produces the same result as decryption. It also has ten pairs of
      "semi-weak keys" [Schn] (a.k.a. "dual keys" [FP074]) for which
      encryption with one key in the pair produces the same result as
      decryption with the other key.

   $ web, Web
      1. (I) /not capitalized/ IDOCs SHOULD NOT capitalize "web" when
      using the term (usually as an adjective) to refer generically to
      technology -- such as web browsers, web servers, HTTP, and HTML --
      that is used in the Web or similar networks.

      2. (I) /capitalized/ IDOCs SHOULD capitalize "Web" when using the
      term (as either a noun or an adjective) to refer specifically to
      the World Wide Web. (Similarly, see: internet.)

      Usage: IDOCs SHOULD NOT use "web" or "Web" in a way that might
      confuse these definitions with the PGP "web of trust". When using
      Web as an abbreviation for "World Wide Web", IDOCs SHOULD fully
      spell out the term at the first instance of usage.

   $ web of trust
      (D) /PGP/ A PKI architecture in which each certificate user
      defines their own trust anchor(s) by depending on personal
      relationships. (See: trust anchor. Compare: hierarchical PKI, mesh
      PKI.)

      Deprecated Usage: IDOCs SHOULD NOT use this term except with
      reference to PGP. This term mixes concepts in potentially
      misleading ways; e.g., this architecture does not depend on World
      Wide Web technology. Instead of this term, IDOCs MAY use "trust-
      file PKI". (See: web, Web).

      Tutorial: This type of architecture does not usually include
      public repositories of certificates. Instead, each certificate
      user builds their own, private repository of trusted public keys
      by making personal judgments about being able to trust certain
      people to be holding properly certified keys of other people. It
      is this set of person-to-person relationships from which the
      architecture gets its name.

   $ web server
      (I) A software process that runs on a host computer connected to a
      network and responds to HTTP requests made by client web browsers.

   $ WEP
      (N) See: Wired Equivalency Protocol.

   $ Wired Equivalent Privacy (WEP)
      (N) A cryptographic protocol that is defined in the IEEE 802.11
      standard and encapsulates the packets on wireless LANs. Usage:
      a.k.a. "Wired Equivalency Protocol".

      Tutorial: The WEP design, which uses RC4 to encrypt both the plain
      text and a CRC, has been shown to be flawed in multiple ways; and
      it also has often suffered from flawed implementation and
      management.

   $ wiretapping
      (I) An attack that intercepts and accesses information contained
      in a data flow in a communication system. (See: active
      wiretapping, end-to-end encryption, passive wiretapping, secondary
      definition under "interception".)

      Usage: Although the term originally referred to making a
      mechanical connection to an electrical conductor that links two
      nodes, it is now used to refer to accessing information from any
      sort of medium used for a link or even from a node, such as a
      gateway or subnetwork switch.

      Tutorial: Wiretapping can be characterized according to intent:
      -  "Active wiretapping" attempts to alter the data or otherwise
         affect the flow.
      -  "Passive wiretapping" only attempts to observe the data flow
         and gain knowledge of information contained in it.

   $ work factor
      1a. (I) /COMPUSEC/ The estimated amount of effort or time that can
      be expected to be expended by a potential intruder to penetrate a
      system, or defeat a particular countermeasure, when using
      specified amounts of expertise and resources. (See: brute force,
      impossible, strength.)

      1b. (I) /cryptography/ The estimated amount of computing power and
      time needed to break a cryptographic system. (See: brute force,
      impossible, strength.)

   $ World Wide Web ("the Web", WWW)
      (N) The global, hypermedia-based collection of information and
      services that is available on Internet servers and is accessed by
      browsers using Hypertext Transfer Protocol and other information
      retrieval mechanisms. (See: web vs. Web, [R2084].)

   $ World Wide Web Consortium (W3C)
      (N) Created in October 1994 to develop and standardize protocols
      to promote the evolution and interoperability of the Web, and now
      consisting of hundreds of member organizations (commercial firms,
      governmental agencies, schools, and others).

      Tutorial: W3C Recommendations are developed through a process
      similar to that of the standards published by other organizations,
      such as the IETF. The W3 Recommendation Track (i.e., standards
      track) has four levels of increasing maturity: Working, Candidate
      Recommendation, Proposed Recommendation, and W3C Recommendation.
      W3C Recommendations are similar to the standards published by
      other organizations. (Compare: Internet Standard, ISO.)

   $ worm
      (I) A computer program that can run independently, can propagate a
      complete working version of itself onto other hosts on a network,
      and may consume system resources destructively. (See: mobile code,
      Morris Worm, virus.)

   $ wrap
      1. (N) To use cryptography to provide data confidentiality service
      for keying material. (See: encrypt, wrapping algorithm, wrapping
      key. Compare: seal, shroud.)

      2. (D) To use cryptography to provide data confidentiality service
      for data in general.

      Deprecated Usage: IDOCs SHOULD NOT use this term with definition 2
      because that duplicates the meaning of the more widely understood
      "encrypt".

   $ wrapping algorithm
      (N) An encryption algorithm that is specifically intended for use
      in encrypting keys. (See: KEK, wrap.)

   $ wrapping key
      (N) Synonym for "KEK". (See: encrypt. Compare: seal, shroud.)

   $ write
      (I) /security model/ A system operation that causes a flow of
      information from a subject to an object. (See: access mode.
      Compare: read.)

   $ WWW
      (I) See: World Wide Web.

   $ X.400
      (N) An ITU-T Recommendation [X400] that is one part of a joint
      ITU-T/ISO multi-part standard (X.400-X.421) that defines the
      Message Handling Systems. (The ISO equivalent is IS 10021, parts
      1-7.) (See: Message Handling Systems.)

   $ X.500
      (N) An ITU-T Recommendation [X500] that is one part of a joint
      ITU-T/ISO multi-part standard (X.500-X.525) that defines the X.500
      Directory, a conceptual collection of systems that provide
      distributed directory capabilities for OSI entities, processes,
      applications, and services. (The ISO equivalent is IS 9594-1 and
      related standards, IS 9594-x.) (See: directory vs. Directory,
      X.509.)

      Tutorial: The X.500 Directory is structured as a tree (the
      Directory Information Tree), and information is stored in
      directory entries. Each entry is a collection of information about
      one object, and each object has a DN. A directory entry is
      composed of attributes, each with a type and one or more values.
      For example, if a PKI uses the Directory to distribute

      certificates, then the X.509 public-key certificate of an end user
      is normally stored as a value of an attribute of type
      "userCertificate" in the Directory entry that has the DN that is
      the subject of the certificate.

   $ X.509
      (N) An ITU-T Recommendation [X509] that defines a framework to
      provide and support data origin authentication and peer entity
      authentication, including formats for X.509 public-key
      certificates, X.509 attribute certificates, and X.509 CRLs. (The
      ISO equivalent is IS 9498-4.) (See: X.500.)

      Tutorial: X.509 describes two "levels" of authentication: "simple
      authentication" and "strong authentication". It recommends, "While
      simple authentication offers some limited protection against
      unauthorized access, only strong authentication should be used as
      the basis for providing secure services."

   $ X.509 attribute certificate
      (N) An attribute certificate in the version 1 (v1) format defined
      by X.509. (The v1 designation for an X.509 attribute certificate
      is disjoint from the v1 designation for an X.509 public-key
      certificate, and from the v1 designation for an X.509 CRL.)

      Tutorial: An X.509 attribute certificate has a "subject" field,
      but the attribute certificate is a separate data structure from
      that subject's public-key certificate. A subject may have multiple
      attribute certificates associated with each of its public-key
      certificates, and an attribute certificate may be issued by a
      different CA than the one that issued the associated public-key
      certificate.

      An X.509 attribute certificate contains a sequence of data items
      and has a digital signature that is computed from that sequence.
      Besides the signature, an attribute certificate contains items 1
      through 9 listed below:

      1. version                 Identifies v1.
      2. subject                 Is one of the following:
         2a. baseCertificateID   Issuer and serial number of an
                                 X.509 public-key certificate.
         2b. subjectName         DN of the subject.
      3. issuer                  DN of the issuer (the CA who signed).
      4. signature               OID of algorithm that signed the cert.
      5. serialNumber            Certificate serial number;
                                 an integer assigned by the issuer.
      6. attCertValidityPeriod   Validity period; a pair of UTCTime
                                 values: "not before" and "not after".

      7. attributes              Sequence of attributes describing the
                                 subject.
      8. issuerUniqueId          Optional, when a DN is not sufficient.
      9. extensions              Optional.

   $ X.509 certificate
      (N) Synonym for "X.509 public-key certificate".

      Usage: IDOCs MAY use this term as an abbreviation of "X.509
      public-key certificate", but only after using the full term at the
      first instance. Otherwise, the term is ambiguous, because X.509
      specifies both public-key certificates and attribute certificates.
      (See: X.509 attribute certificate, X.509 public-key certificate.)

      Deprecated Usage: IDOCs SHOULD NOT use this term as an
      abbreviation of "X.509 attribute certificate", because the term is
      much more commonly used to mean "X.509 public-key certificate"
      and, therefore, is likely to be misunderstood.

   $ X.509 certificate revocation list (CRL)
      (N) A CRL in one of the formats defined by X.509 -- version 1 (v1)
      or version 2 (v2). (The v1 and v2 designations for an X.509 CRL
      are disjoint from the v1 and v2 designations for an X.509 public-
      key certificate, and from the v1 designation for an X.509
      attribute certificate.) (See: certificate revocation.)

      Usage: IDOCs SHOULD NOT refer to an X.509 CRL as a digital
      certificate; however, note that an X.509 CRL does meet this
      Glossary's definition of "digital certificate". That is, like a
      digital certificate, an X.509 CRL makes an assertion and is signed
      by a CA. But instead of binding a key or other attributes to a
      subject, an X.509 CRL asserts that certain previously issued,
      X.509 certificates have been revoked.

      Tutorial: An X.509 CRL contains a sequence of data items and has a
      digital signature computed on that sequence. Besides the
      signature, both v1 and v2 contain items 2 through 6b listed below.
      Version 2 contains item 1 and may optionally contain 6c and 7.

      1. version                 Optional. If present, identifies v2.
      2. signature               OID of the algorithm that signed CRL.
      3. issuer                  DN of the issuer (the CA who signed).
      4. thisUpdate              A UTCTime value.
      5. nextUpdate              A UTCTime value.
      6. revokedCertificates     3-tuples of 6a, 6b, and (optional) 6c:
         6a. userCertificate     A certificate's serial number.
         6b. revocationDate      UTCTime value for the revocation date.
         6c. crlEntryExtensions  Optional.

      7. crlExtensions           Optional.

   $ X.509 public-key certificate
      (N) A public-key certificate in one of the formats defined by
      X.509 -- version 1 (v1), version 2 (v2), or version 3 (v3). (The
      v1 and v2 designations for an X.509 public-key certificate are
      disjoint from the v1 and v2 designations for an X.509 CRL, and
      from the v1 designation for an X.509 attribute certificate.)

      Tutorial: An X.509 public-key certificate contains a sequence of
      data items and has a digital signature computed on that sequence.
      Besides the signature, all three versions contain items 1 through
      7 listed below. Only v2 and v3 certificates may also contain items
      8 and 9, and only v3 may contain item 10.

      1. version                 Identifies v1, v2, or v3.
      2. serialNumber            Certificate serial number;
                                 an integer assigned by the issuer.
      3. signature               OID of algorithm that was used to
                                 sign the certificate.
      4. issuer                  DN of the issuer (the CA who signed).
      5. validity                Validity period; a pair of UTCTime
                                 values: "not before" and "not after".
      6. subject                 DN of entity who owns the public key.
      7. subjectPublicKeyInfo    Public key value and algorithm OID.
      8. issuerUniqueIdentifier  Defined for v2, v3; optional.
      9. subjectUniqueIdentifier Defined for v2, v2; optional.
      10. extensions             Defined only for v3; optional.

   $ X9
      (N) See: "Accredited Standards Committee X9" under "ANSI".

   $ XML
      (N) See: Extensible Markup Language.

   $ XML-Signature.
      (N) A W3C Recommendation (i.e., approved standard) that specifies
      XML syntax and processing rules for creating and representing
      digital signatures (based on asymmetric cryptography) that can be
      applied to any digital content (i.e., any data object) including
      other XML material.

   $ Yellow Book
      (D) /slang/ Synonym for "Computer Security Requirements: Guidance
      for Applying the [U.S.] Department of Defense Trusted Computer
      System Evaluation Criteria in Specific Environments" [CSC3] (See:
      "first law" under "Courtney's laws".)

      Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for
      that or any other document. Instead, use the full proper name of
      the document or, in subsequent references, a conventional
      abbreviation. (See: Deprecated Usage under "Green Book", Rainbow
      Series.)

   $ zero-knowledge proof
      (I) /cryptography/ A proof-of-possession protocol whereby a system
      entity can prove possession of some information to another entity,
      without revealing any of that information. (See: proof-of-
      possession protocol.)

   $ zeroize
      1. (I) Synonym for "erase". (See: sanitize.) Usage: Particularly
      with regard to erasing keys that are stored in a cryptographic
      module.

      2. (O) Erase electronically stored data by altering the contents
      of the data storage so as to prevent the recovery of the data.
      [FP140]

      3. (O) "To remove or eliminate the key from a cryptoequipment or
      fill device." [C4009]

      Usage: The phrase "zeroize the device" normally is used to mean
      erasing all keys stored in the device, but sometimes means erasing
      all keying material in the device, or all cryptographic
      information in the device, or even all sensitive information in
      the device.

   $ zombie
      (I) /slang/ An Internet host computer that has been
      surreptitiously penetrated by an intruder that installed malicious
      daemon software to cause the host to operate as an accomplice in
      attacking other hosts, particularly in distributed attacks that
      attempt denial of service through flooding.

      Deprecated Usage: Other cultures likely use different metaphorical
      terms (such as "robot") for this concept, and some use this term
      for different concepts. Therefore, to avoid international
      misunderstanding, IDOCs SHOULD NOT use this term. Instead, use
      "compromised, coopted computer" or other explicitly descriptive
      terminology. (See: Deprecated Usage under "Green Book".)

   $ zone of control
      (O) /EMSEC/ Synonym for "inspectable space". [C4009] (See:
      TEMPEST.)

5. Security Considerations

   This document mainly defines security terms and recommends how to use
   them. It also provides limited tutorial information about security
   aspects of Internet protocols, but it does not describe in detail the
   vulnerabilities of, or threats to, specific protocols and does not
   definitively describe mechanisms that protect specific protocols.

6. Normative Reference

   [R2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.

7. Informative References

   This Glossary focuses on the Internet Standards Process. Therefore,
   this set of informative references emphasizes international,
   governmental, and industrial standards documents. Some RFCs that are
   especially relevant to Internet security are mentioned in Glossary
   entries in square brackets (e.g., "[R1457]" in the entry for
   "security label") and are listed here; some other RFCs are mentioned
   in parentheses (e.g., "(RFC 959)" in the entry for "File Transport
   Protocol") but are not listed here.

   [A1523]  American National Standards Institute, "American National
            Standard Telecom Glossary", ANSI T1.523-2001.

   [A3092]  ---, "American National Standard Data Encryption Algorithm",
            ANSI X3.92-1981, 30 December 1980.

   [A9009]  ---, "Financial Institution Message Authentication
            (Wholesale)", ANSI X9.9-1986, 15 August 1986.

   [A9017]  ---, "Financial Institution Key Management (Wholesale)",
            X9.17, 4 April 1985. (Defines procedures for manual and
            automated management of keying material and uses DES to
            provide key management for a variety of operational
            environments.)

   [A9042]  ---, "Public key Cryptography for the Financial Service
            Industry: Agreement of Symmetric Keys Using Diffie-Hellman
            and MQV Algorithms", X9.42, 29 January 1999. (See: Diffie-
            Hellman-Merkle.)

   [A9052]  ---, "Triple Data Encryption Algorithm Modes of Operation",
            X9.52-1998, ANSI approval 9 November 1998.

   [A9062]  ---, "Public Key Cryptography for the Financial Services
            Industry: The Elliptic Curve Digital Signature Algorithm
            (ECDSA)", X9.62-1998, ANSI approval 7 January 1999.

   [A9063]  ---, "Public Key Cryptography for the Financial Services
            Industry: Key Agreement and Key Transport Using Elliptic
            Curve Cryptography", X9.63-2001.

   [ACM]    Association for Computing Machinery, "Communications of the
            ACM", July 1998 issue with: M. Yeung, "Digital
            Watermarking"; N. Memom and P. Wong, "Protecting Digital
            Media Content"; and S. Craver, B.-L. Yeo, and M. Yeung,
            "Technical Trials and Legal Tribulations".

   [Ande]   Anderson, J., "Computer Security Technology Planning Study",
            ESD-TR-73-51, Vols. I and II, USAF Electronics Systems Div.,
            Bedford, MA, October 1972. (Available as AD-758206/772806,
            National Technical Information Service, Springfield, VA.)

   [ANSI]   American National Standards Institute, "Role Based Access
            Control", Secretariat, Information Technology Industry
            Council, BSR INCITS 359, DRAFT, 10 November 2003.

   [Army]   U.S. Army Corps of Engineers, "Electromagnetic Pulse (EMP)
            and Tempest Protection for Facilities", EP 1110-3-2, 31
            December 1990.

   [B1822]  Bolt Baranek and Newman Inc., "Appendix H: Interfacing a
            Host to a Private Line Interface", in "Specifications for
            the Interconnection of a Host and an IMP", BBN Report No.
            1822, revised, December 1983.

   [B4799]  ---, "A History of the Arpanet: The First Decade", BBN
            Report No. 4799, April 1981.

   [Bell]   Bell, D. and L. LaPadula, "Secure Computer Systems:
            Mathematical Foundations and Model", M74-244, The MITRE
            Corporation, Bedford, MA, May 1973. (Available as AD-771543,
            National Technical Information Service, Springfield, VA.)

   [Biba]   K. Biba, "Integrity Considerations for Secure Computer
            Systems", ESD-TR-76-372, USAF Electronic Systems Division,
            Bedford, MA, April 1977.

   [BN89]   Brewer, D. and M. Nash, "The Chinese wall security policy",
            in "Proceedings of IEEE Symposium on Security and Privacy",
            May 1989, pp. 205-214.

   [BS7799] British Standards Institution, "Information Security
            Management, Part 1: Code of Practice for Information
            Security Management", BS 7799-1:1999, 15 May 1999.

            ---, "Information Security Management, Part 2: Specification
            for Information Security Management Systems", BS 7799-
            2:1999, 15 May 1999.

   [C4009]  Committee on National Security Systems (U.S. Government),
            "National Information Assurance (IA) Glossary", CNSS
            Instruction No. 4009, revised June 2006.

   [CCIB]   Common Criteria Implementation Board, "Common Criteria for
            Information Technology Security Evaluation, Part 1:
            Introduction and General Model", version 2.0, CCIB-98-026,
            May 1998.

   [Chau]   D. Chaum, "Untraceable Electronic Mail, Return Addresses,
            and Digital Pseudonyms", in "Communications of the ACM",
            vol. 24, no. 2, February 1981, pp. 84-88.

   [Cheh]   Cheheyl, M., Gasser, M., Huff, G., and J. Millen, "Verifying
            Security", in "ACM Computing Surveys", vol. 13, no. 3,
            September 1981, pp. 279-339.

   [Chris]  Chrissis, M. et al, 1993. "SW-CMM [Capability Maturity Model
            for Software Version", Release 3.0, Software Engineering
            Institute, Carnegie Mellon University, August 1996.

   [CIPSO]  Trusted Systems Interoperability Working Group, "Common IP
            Security Option", version 2.3, 9 March 1993.

   [Clark]  Clark, D. and D. Wilson, "A Comparison of Commercial and
            Military computer Security Policies", in "Proceedings of the
            IEEE Symposium on Security and Privacy", April 1987, pp.
            184-194.

   [Cons]   NSA, "Consistency Instruction Manual for Development of U.S.
            Government Protection Profiles for Use in Basic Robustness
            Environments", Release 2.0, 1 March 2004

   [CORBA]  Object Management Group, Inc., "CORBAservices: Common Object
            Service Specification", December 1998.

   [CSC1]   U.S. DoD Computer Security Center, "Department of Defense
            Trusted Computer System Evaluation Criteria", CSC-STD-001-
            83, 15 August 1983. (Superseded by [DoD1].)

   [CSC2]   ---, "Department of Defense Password Management Guideline",
            CSC-STD-002-85, 12 April 1985.

   [CSC3]   ---, "Computer Security Requirements: Guidance for Applying
            the Department of Defense Trusted Computer System Evaluation
            Criteria in Specific Environments", CSC-STD-003-85, 25 June
            1985.

   [CSOR]   U.S. Department of Commerce, "General Procedures for
            Registering Computer Security Objects", National Institute
            of Standards Interagency Report 5308, December 1993.

   [Daem]   Daemen, J. and V. Rijmen, "Rijndael, the advanced encryption
            standard", in "Dr. Dobb's Journal", vol. 26, no. 3, March
            2001, pp. 137-139.

   [DC6/9]  Director of Central Intelligence, "Physical Security
            Standards for Sensitive Compartmented Information
            Facilities", DCI Directive 6/9, 18 November 2002.

   [Denn]   Denning, D., "A Lattice Model of Secure Information Flow",
            in "Communications of the ACM", vol. 19, no. 5, May 1976,
            pp. 236-243.

   [Denns]  Denning, D. and P. Denning, "Data Security", in "ACM
            Computing Surveys", vol. 11, no. 3, September 1979, pp. 227-
            249.

   [DH76]   Diffie, W. and M. Hellman, "New Directions in Cryptography",
            in "IEEE Transactions on Information Theory", vol. IT-22,
            no. 6, November 1976, pp. 644-654. (See: Diffie-Hellman-
            Merkle.)

   [DoD1]   U.S. DoD, "Department of Defense Trusted Computer System
            Evaluation Criteria", DoD 5200.28-STD, 26 December 1985.
            (Supersedes [CSC1].) (Superseded by DoD Directive 8500.1.)

   [DoD4]   ---, "NSA Key Recovery Assessment Criteria", 8 June 1998.

   [DoD5]   ---, Directive 5200.1, "DoD Information Security Program",
            13 December 1996.

   [DoD6]   ---, "Department of Defense Technical Architecture Framework
            for Information Management, Volume 6: Department of Defense
            (DoD) Goal Security Architecture", Defense Information
            Systems Agency, Center for Standards, version 3.0, 15 April
            1996.

   [DoD7]   ---, "X.509 Certificate Policy for the United States
            Department of Defense", version 7, 18 December 2002.
            (Superseded by [DoD9].)

   [DoD9]   ---, "X.509 Certificate Policy for the United States
            Department of Defense", version 9, 9 February 2005.

   [DoD10]  ---, "DoD Architecture Framework, Version 1: Deskbook", 9
            February 2004.

   [DSG]    American Bar Association, "Digital Signature Guidelines:
            Legal Infrastructure for Certification Authorities and
            Secure Electronic Commerce", Chicago, IL, 1 August 1996.
            (See: [PAG].)

   [ElGa]   El Gamal, T., "A Public-Key Cryptosystem and a Signature
            Scheme Based on Discrete Logarithms", in "IEEE Transactions
            on Information Theory", vol. IT-31, no. 4, 1985, pp. 469-
            472.

   [EMV1]   Europay International S.A., MasterCard International
            Incorporated, and Visa International Service Association,
            "EMV '96 Integrated Circuit Card Specification for Payment
            Systems", version 3.1.1, 31 May 1998.

   [EMV2]   ---, "EMV '96 Integrated Circuit Card Terminal Specification
            for Payment Systems", version 3.1.1, 31 May 1998.

   [EMV3]   ---, "EMV '96 Integrated Circuit Card Application
            Specification for Payment Systems", version 3.1.1, 31 May
            1998.

   [F1037]  U.S. General Services Administration, "Glossary of
            Telecommunications Terms", FED STD 1037C, 7 August 1996.

   [For94]  Ford, W., "Computer Communications Security: Principles,
            Standard Protocols and Techniques", ISBN 0-13-799453-2,
            1994.

   [For97]  --- and M. Baum, "Secure Electronic Commerce: Building the
            Infrastructure for Digital Signatures and Encryption", ISBN
            0-13-476342-4, 1994.

   [FP001]  U.S. Department of Commerce, "Code for Information
            Interchange", Federal Information Processing Standards
            Publication (FIPS PUB) 1, 1 November 1968.

   [FP031]  ---, "Guidelines for Automatic Data Processing Physical
            Security and Risk Management", FIPS PUB 31, June 1974.

   [FP039]  ---, "Glossary for Computer Systems Security", FIPS PUB 39,
            15 February 1976.

   [FP041]  ---, "Computer Security Guidelines for Implementing the
            Privacy Act of 1974", FIPS PUB 41, 30 May 1975.

   [FP046]  ---, "Data Encryption Standard (DES)", FIPS PUB 46-3, 25
            October 1999.

   [FP074]  ---, "Data Encryption Standard (DES)", FIPS PUB 46-3, 25
            October 1999.

   [FP081]  ---, "DES Modes of Operation", FIPS PUB 81, 2 December 1980.

   [FP087]  ---, "Guidelines for ADP Contingency Planning", FIPS PUB 87,
            27 March 1981.

   [FP102]  ---, "Guideline for Computer Security Certification and
            Accreditation", FIPS PUB 102, 27 September 1983.

   [FP113]  ---, "Computer Data Authentication", FIPS PUB 113, 30 May
            1985.

   [FP140]  ---, "Security Requirements for Cryptographic Modules", FIPS
            PUB 140-2, 25 May 2001; with change notice 4, 3 December
            2002.

   [FP151]  ---, "Portable Operating System Interface (POSIX) -- System
            Application Program Interface [C Language]", FIPS PUB 151-2,
            12 May 1993

   [FP180]  ---, "Secure Hash Standard", FIPS PUB 180-2, August 2000;
            with change notice 1, 25 February 2004.

   [FP185]  ---, "Escrowed Encryption Standard", FIPS PUB 185, 9
            February 1994.

   [FP186]  ---, "Digital Signature Standard (DSS)", FIPS PUB 186-2, 27
            June 2000; with change notice 1, 5 October 2001.

   [FP188]  ---, "Standard Security Label for Information Transfer",
            FIPS PUB 188, 6 September 1994.

   [FP191]  ---, "Guideline for the Analysis of Local Area Network
            Security", FIPS PUB 191, 9 November 1994.

   [FP197]  ---, "Advanced Encryption Standard", FIPS PUB 197, 26
            November 2001.

   [FP199]  ---, "Standards for Security Categorization of Federal
            Information and Information Systems ", FIPS PUB 199,
            December 2003.

   [FPKI]   ---, "Public Key Infrastructure (PKI) Technical
            Specifications: Part A -- Technical Concept of Operations",
            NIST, 4 September 1998.

   [Gass]   Gasser, M., "Building a Secure Computer System", Van
            Nostrand Reinhold Company, New York, 1988, ISBN 0-442-
            23022-2.

   [Gray]   Gray, J. and A. Reuter, "Transaction Processing: Concepts
            and Techniques", Morgan Kaufmann Publishers, Inc., 1993.

   [Hafn]   Hafner, K. and M. Lyon, "Where Wizards Stay Up Late: The
            Origins of the Internet", Simon & Schuster, New York, 1996.

   [Huff]   Huff, G., "Trusted Computer Systems -- Glossary", MTR 8201,
            The MITRE Corporation, March 1981.

   [I3166]  International Standards Organization, "Codes for the
            Representation of Names of Countries and Their Subdivisions,
            Part 1: Country Codes", ISO 3166-1:1997.

            ---, "Codes for the Representation of Names of Countries and
            Their Subdivisions, Part 2: Country Subdivision Codes",
            ISO/DIS 3166-2.

            ---, "Codes for the Representation of Names of Countries and
            Their Subdivisions, Part 3: Codes for Formerly Used Names of
            Countries", ISO/DIS 3166-3.

   [I7498-1] ---, "Information Processing Systems -- Open Systems
            Interconnection Reference Model, [Part 1:] Basic Reference
            Model", ISO/IEC 7498-1. (Equivalent to ITU-T Recommendation
            X.200.)

   [I7498-2] ---, "Information Processing Systems -- Open Systems
            Interconnection Reference Model, Part 2: Security
            Architecture", ISO/IEC 7499-2.

   [I7498-4] ---, "Information Processing Systems -- Open Systems
            Interconnection Reference Model, Part 4: Management
            Framework", ISO/IEC 7498-4.

   [I7812]  ---, "Identification cards -- Identification of Issuers,
            Part 1: Numbering System", ISO/IEC 7812-1:1993

            ---, "Identification cards -- Identification of Issuers,
            Part 2: Application and Registration Procedures", ISO/IEC
            7812-2:1993.

   [I8073]  ---, "Information Processing Systems -- Open Systems
            Interconnection, Transport Protocol Specification", ISO IS
            8073.

   [I8327]  ---, "Information Processing Systems -- Open Systems
            Interconnection, Session Protocol Specification", ISO IS
            8327.

   [I8473]  ---, "Information Processing Systems -- Open Systems
            Interconnection, Protocol for Providing the Connectionless
            Network Service", ISO IS 8473.

   [I8802-2] ---, "Information Processing Systems -- Local Area
            Networks, Part 2: Logical Link Control", ISO IS 8802-2.
            (Equivalent to IEEE 802.2.)

   [I8802-3] ---, "Information Processing Systems -- Local Area
            Networks, Part 3: Carrier Sense Multiple Access with
            Collision Detection (CSMA/CD) Access Method and Physical
            Layer Specifications", ISO IS 8802-3. (Equivalent to IEEE
            802.3.)

   [I8823]  ---, "Information Processing Systems -- Open Systems
            Interconnection -- Connection-Oriented Presentation Protocol
            Specification", ISO IS 8823.

   [I9945]  "Portable Operating System Interface for Computer
            Environments", ISO/IEC 9945-1: 1990.

   [IATF]   NSA, "Information Assurance Technical Framework", Release 3,
            NSA, September 2000. (See: IATF.)

   [IDSAN]  ---, "Intrusion Detection System Analyzer Protection
            Profile", version 1.1, NSA, 10 December 2001.

   [IDSSC]  ---, "Intrusion Detection System Scanner Protection
            Profile", version 1.1, NSA, 10 December 2001.

   [IDSSE]  ---, "Intrusion Detection System Sensor Protection Profile",
            version 1.1, NSA, 10 December 2001.

   [IDSSY]  ---, "Intrusion Detection System", version 1.4, NSA, 4
            February 2002.

   [Ioan]   Ioannidis, J. and M. Blaze, "The Architecture and
            Implementation of Network Layer Security in UNIX", in "UNIX
            Security IV Symposium", October 1993, pp. 29-39.

   [ITSEC]  "Information Technology Security Evaluation Criteria
            (ITSEC): Harmonised Criteria of France, Germany, the
            Netherlands, and the United Kingdom", version 1.2, U.K.
            Department of Trade and Industry, June 1991.

   [JP1]    U.S. DoD, "Department of Defense Dictionary of Military and
            Associated Terms", Joint Publication 1-02, as amended
            through 13 June 2007.

   [John]   Johnson, N. and S. Jajodia, "Exploring Steganography; Seeing
            the Unseen", in "IEEE Computer", February 1998, pp. 26-34.

   [Kahn]   Kahn, D., "The Codebreakers: The Story of Secret Writing",
            The Macmillan Company, New York, 1967.

   [Knut]   Knuth, D., Chapter 3 ("Random Numbers") of Volume 2
            ("Seminumerical Algorithms") of "The Art of Computer
            Programming", Addison-Wesley, Reading, MA, 1969.

   [Kuhn]   Kuhn, M. and R. Anderson, "Soft Tempest: Hidden Data
            Transmission Using Electromagnetic Emanations", in David
            Aucsmith, ed., "Information Hiding, Second International
            Workshop, IH'98", Portland, Oregon, USA, 15-17 April 1998,
            LNCS 1525, Springer-Verlag, ISBN 3-540-65386-4, pp. 124-142.

   [Land]   Landwehr, C., "Formal Models for Computer Security", in "ACM
            Computing Surveys", vol. 13, no. 3, September 1981, pp. 247-
            278.

   [Larm]   Larmouth, J., "ASN.1 Complete", Open System Solutions, 1999
            (a freeware book).

   [M0404]  U.S. Office of Management and Budget, "E-Authentication
            Guidance for Federal Agencies", Memorandum M-04-04, 16
            December 2003.

   [Mene]   Menezes, A. et al, "Some Key Agreement Protocols Providing
            Implicit Authentication", in "The 2nd Workshop on Selected
            Areas in Cryptography", 1995.

   [Moor]   Moore, A. et al, "Attack Modeling for Information Security
            and Survivability", Carnegie Mellon University / Software
            Engineering Institute, CMU/SEI-2001-TN-001, March 2001.

   [Murr]   Murray, W., "Courtney's Laws of Security", in "Infosecurity
            News", March/April 1993, p. 65.

   [N4001]  National Security Telecommunications and Information System
            Security Committee, "Controlled Cryptographic Items",
            NSTISSI No. 4001, 25 March 1985.

   [N4006]  ---, "Controlled Cryptographic Items", NSTISSI No. 4006, 2
            December 1991.

   [N7003]  ---, "Protective Distribution Systems", NSTISSI No. 7003, 13
            December 1996.

   [NCS01]  National Computer Security Center, "A Guide to Understanding
            Audit in Trusted Systems", NCSC-TG-001, 1 June 1988. (See:
            Rainbow Series.)

   [NCS03]  ---, "Information System Security Policy Guideline", I942-
            TR-003, version 1, July 1994. (See: Rainbow Series.)

   [NCS04]  ---, "Glossary of Computer Security Terms", NCSC-TG-004,
            version 1, 21 October 1988. (See: Rainbow Series.)

   [NCS05]  ---, "Trusted Network Interpretation of the Trusted Computer
            System Evaluation Criteria", NCSC-TG-005, version 1, 31 July
            1987. (See: Rainbow Series.)

   [NCS25]  ---, "A Guide to Understanding Data Remanence in Automated
            Information Systems", NCSC-TG-025, version 2, September
            1991. (See: Rainbow Series.)

   [NCSSG]  National Computer Security Center, "COMPUSECese: Computer
            Security Glossary", NCSC-WA-001-85, Edition 1, 1 October
            1985. (See: Rainbow Series.)

   [NRC91]  National Research Council, "Computers At Risk: Safe
            Computing in the Information Age", National Academy Press,
            1991.

   [NRC98]  Schneider, F., ed., "Trust in Cyberspace", National Research
            Council, National Academy of Sciences, 1998.

   [Padl]   Padlipsky, M., "The Elements of Networking Style", 1985,
            ISBN 0-13-268111-0.

   [PAG]    American Bar Association, "PKI Assessment Guidelines",
            version 1.0, 10 May 2002. (See: [DSG].)

   [Park]   Parker, D., "Computer Security Management", ISBN 0-8359-
            0905-0, 1981

   [Perr]   Perrine, T. et al, "An Overview of the Kernelized Secure
            Operating System (KSOS)", in "Proceedings of the 7th DoD/NBS
            Computer Security Conference", 24-26 September 1984.

   [PGP]    Garfinkel, S.. "PGP: Pretty Good Privacy", O'Reilly &
            Associates, Inc., Sebastopol, CA, 1995.

   [PKCS]   Kaliski Jr., B., "An Overview of the PKCS Standards", RSA
            Data Security, Inc., 3 June 1991.

   [PKC05]  RSA Laboratories, "PKCS #5: Password-Based Encryption
            Standard ", version 1.5, 1 November 1993. (See: RFC 2898.)

   [PKC07]  ---, "PKCS #7: Cryptographic Message Syntax Standard",
            version 1.5, 1 November 1993. (See: RFC 2315.)

   [PKC10]  ---, "PKCS #10: Certification Request Syntax Standard",
            version 1.0, 1 November 1993.

   [PKC11]  ---, "PKCS #11: Cryptographic Token Interface Standard",
            version 1.0, 28 April 1995.

   [PKC12]  ---, "PKCS #12: Personal Information Exchange Syntax",
            version 1.0, 24 June 1995.

   [R1108]  Kent, S., "U.S. Department of Defense Security Options for
            the Internet Protocol", RFC 1108, November 1991.

   [R1135]  Reynolds, J., "The Helminthiasis of the Internet", RFC 1135,
            December 1989

   [R1208]  Jacobsen, O. and D. Lynch, "A Glossary of Networking Terms",
            RFC 1208, March 1991.

   [R1281]  Pethia, R., Crocker, S., and B. Fraser, "Guidelines for
            Secure Operation of the Internet", RFC 1281, November 1991.

   [R1319]  Kaliski, B., "The MD2 Message-Digest Algorithm", RFC 1319,
            April 1992.

   [R1320]  Rivest, R., "The MD4 Message-Digest Algorithm", RFC 1320,
            April 1992.

   [R1321]  ---, "The MD5 Message-Digest Algorithm", RFC 1321, April
            1992.

   [R1334]  Lloyd, B. and W. Simpson, "PPP Authentication Protocols",
            RFC 1334, October 1992.

   [R1413]  St. Johns, M., "Identification Protocol", RFC 1413, February
            1993.

   [R1421]  Linn, J., "Privacy Enhancement for Internet Electronic Mail,
            Part I: Message Encryption and Authentication Procedures",
            RFC 1421, February 1993.

   [R1422]  Kent, S., "Privacy Enhancement for Internet Electronic Mail,
            Part II: Certificate-Based Key Management", RFC 1422,
            February 1993.

   [R1455]  Eastlake 3rd, D., "Physical Link Security Type of Service",
            RFC 1455, May 1993.

   [R1457]  Housley, R., "Security Label Framework for the Internet",
            RFC 1457, May 1993.

   [R1492]  Finseth, C., "An Access Control Protocol, Sometimes Called
            TACACS", RFC 1492, July 1993.

   [R1507]  Kaufman, C., "DASS: Distributed Authentication Security
            Service", RFC 1507, September 1993.

   [R1731]  Myers, J., "IMAP4 Authentication Mechanisms", RFC 1731,
            December 1994.

   [R1734]  ---, "POP3 AUTHentication Command", RFC 1734, Dec, 1994.

   [R1760]  Haller, N., "The S/KEY One-Time Password System", RFC 1760,
            February 1995.

   [R1824]  Danisch, H., "The Exponential Security System TESS: An
            Identity-Based Cryptographic Protocol for Authenticated Key-
            Exchange (E.I.S.S.-Report 1995/4)", RFC 1824, August 1995.

   [R1828]  Metzger, P. and W. Simpson, "IP Authentication using Keyed
            MD5", RFC 1828, August 1995.

   [R1829]  Karn, P., Metzger, P., and W. Simpson, "The ESP DES-CBC
            Transform", RFC 1829, August 1995.

   [R1848]  Crocker, S., Freed, N., Galvin, J., and S. Murphy, "MIME
            Object Security Services", RFC 1848, October 1995.

   [R1851]  Karn, P., Metzger, P., and W. Simpson, "The ESP Triple DES
            Transform", RFC 1851, September 1995.

   [R1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and L.
            Jones, "SOCKS Protocol Version 5", RFC 1928, March 1996.

   [R1958]  Carpenter, B., "Architectural Principles of the Internet",
            RFC 1958, June 1996.

   [R1983]  Malkin, G., "Internet Users' Glossary", FYI 18, RFC 1983,
            August 1996.

   [R1994]  Simpson, W., "PPP Challenge Handshake Authentication
            Protocol (CHAP)", RFC 1994, August 1996.

   [R2078]  Linn, J., "Generic Security Service Application Program
            Interface, Version 2", RFC 2078, January 1997. (Superseded
            by RFC 2743.)

   [R2084]  Bossert, G., Cooper, S., and W. Drummond, "Considerations
            for Web Transaction Security", RFC 2084, January 1997.

   [R2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104, February
            1997.

   [R2144]  Adams, C., "The CAST-128 Encryption Algorithm", RFC 2144,
            May 1997.

   [R2179]  Gwinn, A., "Network Security For Trade Shows", RFC 2179,
            July 1997.

   [R2195]  Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP
            AUTHorize Extension for Simple Challenge/Response", RFC
            2195, September 1997.

   [R2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
            September 1997.

   [R2202]  Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC-
            SHA-1", RFC 2202, Sep. 1997.

   [R2222]  Myers, J., "Simple Authentication and Security Layer
            (SASL)", RFC 2222, October 1997.

   [R2289]  Haller, N., Metz, C., Nesser, P., and M. Straw, "A One-Time
            Password System", STD 61, RFC 2289, February 1998.

   [R2323]  Ramos, A., "IETF Identification and Security Guidelines",
            RFC 2323, 1 April 1998. (Intended for humorous entertainment
            -- "please laugh loud and hard" -- and does not contain
            serious security information.)

   [R2350]  Brownlee, N. and E. Guttman, "Expectations for Computer
            Security Incident Response", BCP 21, RFC 2350, June 1998.

   [R2356]  Montenegro, G. and V. Gupta, "Sun's SKIP Firewall Traversal
            for Mobile IP", RFC 2356, June 1998.

   [R2401]  Kent, S. and R. Atkinson, "Security Architecture for the
            Internet Protocol", RFC 2401, November 1998.

   [R2402]  ---, "IP Authentication Header", RFC 2402, November 1998.

   [R2403]  Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within ESP
            and AH", RFC 2403, November 1998.

   [R2404]  ---, "The Use of HMAC-SHA-1-96 within ESP and AH", RFC 2404,
            November 1998.

   [R2405]  Madson, C. and N. Doraswamy, "The ESP DES-CBC Cipher
            Algorithm With Explicit IV", RFC 2405, November 1998.

   [R2406]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
            (ESP)", RFC 2406, November 1998.

   [R2407]  Piper, D. "The Internet IP Security Domain of Interpretation
            for ISAKMP", RFC 2407, November 1998.

   [R2408]  Maughan, D., Schertler, M., Schneider, M., and J. Turner,
            "Internet Security Association and Key Management Protocol
            (ISAKMP)", RFC 2408, November 1998.

   [R2410]  Glenn, R. and S. Kent, "The NULL Encryption Algorithm and
            Its Use With IPsec", RFC 2410, November 1998.

   [R2412]  Orman, H., "The OAKLEY Key Determination Protocol", RFC
            2412, November 1998.

   [R2451]  Pereira, R. and R. Adams, "The ESP CBC-Mode Cipher
            Algorithms", RFC 2451, November 1998.

   [R2504]  Guttman, E., Leong, L., and G. Malkin, "Users' Security
            Handbook", RFC 2504, February 1999.

   [R2560]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
            Adams, "X.509 Internet Public Key Infrastructure Online
            Certificate Status Protocol - OCSP", RFC 2560, June 1999.

   [R2612]  Adams, C. and J. Gilchrist, "The CAST-256 Encryption
            Algorithm", RFC 2612, June 1999.

   [R2628]  Smyslov, V., "Simple Cryptographic Program Interface (Crypto
            API)", RFC 2628, June 1999.

   [R2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
            2631, June 1999. (See: Diffie-Hellman-Merkle.)

   [R2634]  Hoffman, P., "Enhanced Security Services for S/MIME", RFC
            2634, June 1999.

   [R2635]  Hambridge, S. and A. Lunde, "DON'T SPEW: A Set of Guidelines
            for Mass Unsolicited Mailings and Postings", RFC 2635, June
            1999.

   [R2660]  Rescorla, E. and A. Schiffman, "The Secure HyperText
            Transfer Protocol", RFC 2660, August 1999.

   [R2743]  Linn, J., "Generic Security Service Application Program
            Interface Version 2, Update 1", RFC 2743, January 2000.

   [R2773]  Housley, R., Yee, P., and W. Nace, "Encryption using KEA and
            SKIPJACK", RFC 2773, February 2000.

   [R2801]  Burdett, D., "Internet Open Trading Protocol - IOTP, Version
            1.0", RFC 2801, April 2000.

   [R2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
            Defeating Denial of Service Attacks which employ IP Source
            Address Spoofing", BCP 38, RFC 2827, May 2000.

   [R2865]  Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
            Authentication Dial In User Service (RADIUS)", RFC 2865,
            June 2000.

   [R3060]  Moore, B., Ellesson, E., Strassner, J., and A. Westerinen,
            "Policy Core Information Model -- Version 1 Specification",
            RFC 3060, February 2001.

   [R3198]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
            M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
            J., and S. Waldbusser, "Terminology for Policy-Based
            Management", RFC 3198, November 2001.

   [R3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
            X.509 Public Key Infrastructure Certificate and Certificate
            Revocation List (CRL) Profile", RFC 3280, April 2002.

   [R3547]  Baugher, M., Weis, B., Hardjono, T., and H. Harney, "Group
            Domain of Interpretation", RFC 3547, July 2003.

   [R3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text
            on Security Considerations", RFC 3552, July 2003.

   [R3647]  Chokhani, S., Ford, W., Sabett, R., Merrill, C., and S. Wu,
            "Internet X.509 Public Key Infrastructure Certificate Policy
            and Certification Practices Framework", RFC 3647, November
            2003.

   [R3739]  Santesson, S., Nystrom, M., and T. Polk, "Internet X.509
            Public Key Infrastructure: Qualified Certificates Profile",
            RFC 3739, March 2004.

   [R3740]  Hardjono, T. and B. Weis, "The Multicast Group Security
            Architecture", RFC 3740, March 2004.

   [R3748]  Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
            Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
            3748, June 2004.

   [R3766]  Orman, H. and P. Hoffman, "Determining Strengths For Public
            Keys Used For Exchanging Symmetric Keys", BCP 86, RFC 3766,
            April 2004.

   [R3820]  Tuecke, S., Welch, V., Engert, D., Pearlman, L., and M.
            Thompson, "Internet X.509 Public Key Infrastructure (PKI)
            Proxy Certificate Profile", RFC 3820, June 2004.

   [R3851]  Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
            (S/MIME) Version 3.1 Message Specification", RFC 3851, July
            2004.

   [R3871]  Jones, G., "Operational Security Requirements for Large
            Internet Service Provider (ISP) IP Network Infrastructure",
            RFC 3871, September 2004.

   [R4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
            Rose, "DNS Security Introduction and Requirements", RFC
            4033, March 2005.

   [R4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
            Rose, "Resource Records for the DNS Security Extensions",
            RFC 4034,  March 2005.

   [R4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
            Rose, "Protocol Modifications for the DNS Security
            Extensions", RFC 4035, March 2005.

   [R4086]  Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness
            Requirements for Security", BCP 106, RFC 4086, June 2005.

   [R4120]  Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
            Kerberos Network Authentication Service (V5)", RFC 4120,
            July 2005.

   [R4158]  Cooper, M., Dzambasow, Y., Hesse, P., Joseph, S., and R.
            Nicholas, "Internet X.509 Public Key Infrastructure:
            Certification Path Building", RFC 4158, September 2005.

   [R4210]  Adams, C., Farrell, S., Kause, T., and T. Mononen, "Internet
            X.509 Public Key Infrastructure Certificate Management
            Protocol (CMP)", RFC 4210, September 2005.

   [R4301]  Kent, S. and K. Seo, "Security Architecture for the Internet
            Protocol", RFC 4301, December 2005.

   [R4302]  Kent, S., "IP Authentication Header", RFC 4302, December
            2005.

   [R4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
            4303, December 2005.

   [R4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", RFC
            4306, December 2005.

   [R4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.1", RFC 4346, April 2006.

   [R4422]  Melnikov, A. and K. Zeilenga, "Simple Authentication and
            Security Layer (SASL)", RFC 4422, June 2006.

   [Raym]   Raymond, E., ed., "The On-Line Hacker Jargon File", version
            4.0.0, 24 July 1996. (See: http://www.catb.org/~esr/jargon
            for the latest version. Also, "The New Hacker's Dictionary",
            3rd edition, MIT Press, September 1996, ISBN 0-262-68092-0.)

   [Roge]   Rogers, H., "An Overview of the CANEWARE Program", in
            "Proceedings of the 10th National Computer Security
            Conference", NIST and NCSC, September 1987.

   [RSA78]  Rivest, R., A. Shamir, and L. Adleman, "A Method for
            Obtaining Digital Signatures and Public-Key Cryptosystems",
            in "Communications of the ACM", vol. 21, no. 2, February
            1978, pp. 120-126.

   [RSCG]   NSA, "Router Security Configuration Guide: Principles and
            Guidance for Secure Configuration of IP Routers, with
            Detailed Instructions for Cisco Systems Routers", version
            1.1c, C4-040R-02, 15 December 2005, available at
            http://www.nsa.gov/snac/routers/C4-040R-02.pdf.

   [Russ]   Russell, D. et al, Chapter 10 ("TEMPEST") of "Computer
            Security Basics", ISBN 0-937175-71-4, 1991.

   [SAML]   Organization for the Advancement of Structured Information
            Standards (OASIS), "Assertions and Protocol for the OASIS
            Security Assertion Markup Language (SAML)", version 1.1, 2
            September 2003.

   [Sand]   Sandhu, R. et al, "Role-Based Access Control Models", in
            "IEEE Computer", vol. 29, no. 2, February 1996, pp. 38-47.

   [Schn]   Schneier, B., "Applied Cryptography Second Edition", John
            Wiley & Sons, Inc., New York, 1996.

   [SDNS3]  U.S. DoD, NSA, "Secure Data Network Systems, Security
            Protocol 3 (SP3)", document SDN.301, Revision 1.5, 15 May
            1989.

   [SDNS4]  ---, "Secure Data Network Systems, Security Protocol 4
            (SP4)", document SDN.401, Revision 1.2, 12 July 1988.

   [SDNS7]  ---, "Secure Data Network Systems, Message Security Protocol
            (MSP)", SDN.701, Revision 4.0, 7 June 1996, with
            "Corrections to Message Security Protocol, SDN.701, Rev 4.0,
            96-06-07", 30 Aug, 1996.

   [SET1]   MasterCard and Visa, "SET Secure Electronic Transaction
            Specification, Book 1: Business Description", version 1.0,
            31 May 1997.

   [SET2]   ---, "SET Secure Electronic Transaction Specification, Book
            2: Programmer's Guide", version 1.0, 31 May 1997.

   [SKEME]  Krawczyk, H., "SKEME: A Versatile Secure Key Exchange
            Mechanism for Internet", in "Proceedings of the 1996
            Symposium on Network and Distributed Systems Security".

   [SKIP]   "SKIPJACK and KEA Algorithm Specifications", version 2.0, 22
            May 1998, and "Clarification to the SKIPJACK Algorithm
            Specification", 9 May 2002 (available from NIST Computer
            Security Resource Center).

   [SP12]   NIST, "An Introduction to Computer Security: The NIST
            Handbook", Special Publication 800-12.

   [SP14]   Swanson, M. et al (NIST), "Generally Accepted Principles and
            Practices for Security Information Technology Systems",
            Special Publication 800-14, September 1996.

   [SP15]   Burr, W. et al (NIST), "Minimum Interoperability
            Specification for PKI Components (MISPC), Version 1",
            Special Publication 800-15, September 1997.

   [SP22]   Rukhin, A. et al (NIST), "A Statistical Test Suite for
            Random and Pseudorandom Number Generators for Cryptographic
            Applications", Special Publication 800-15, 15 May 2001.

   [SP27]   Stoneburner, G. et al (NIST), "Engineering Principles for
            Information Technology Security (A Baseline for Achieving
            Security)", Special Publication 800-27 Rev A, June 2004.

   [SP28]   Jansen, W. (NIST), "Guidelines on Active Content and Mobile
            Code", Special Publication 800-28, October 2001.

   [SP30]   Stoneburner, G. et al (NIST), "Risk Management Guide for
            Information Technology Systems", Special Publication 800-30,
            October 2001.

   [SP31]   Bace, R. et al (NIST), "Intrusion Detection Systems",
            Special Publication 800-31.

   [SP32]   Kuhn, D. (NIST), "Introduction to Public Key Technology and
            the Federal PKI Infrastructure ", Special Publication
            800-32, 26 February 2001.

   [SP33]   Stoneburner, G. (NIST), "Underlying Technical Models for
            Information Technology Security", Special Publication
            800-33, December 2001.

   [SP37]   Ross, R. et al (NIST), "Guide for the Security Certification
            and Accreditation of Federal Information Systems", Special
            Publication 800-37, May 2004.

   [SP38A]  Dworkin, M. (NIST), "Recommendation for Block Cipher Modes
            of Operation: Methods and Techniques", Special Publication
            800-38A, 2001 Edition, December 2001.

   [SP38B]  ---, "Recommendation for Block Cipher Modes of Operation:
            The CMAC Mode for Authentication", Special Publication
            800-38B, May 2005.

   [SP38C]  ---, "Recommendation for Block Cipher Modes of Operation:
            The CCM Mode for Authentication and Confidentiality",
            Special Publication 800-38C, May 2004.

   [SP41]   Wack, J. et al (NIST), "Guidelines on Firewalls and Firewall
            Policy", Special Publication 800-41, January 2002.

   [SP42]   ---, "Guideline on Network Security Testing", Special
            Publication 800-42, October 2003.

   [SP56]   NIST, "Recommendations on Key Establishment Schemes", Draft
            2.0, Special Publication 800-63, January 2003.

   [SP57]   ---, "Recommendation for Key Management", Part 1 "General
            Guideline" and Part 2 "Best Practices for Key Management
            Organization", Special Publication 800-57, DRAFT, January
            2003.

   [SP61]   Grance, T. et al (NIST), "Computer Security Incident
            Handling Guide", Special Publication 800-57, January 2003.

   [SP63]   Burr, W. et al (NIST), "Electronic Authentication
            Guideline", Special Publication 800-63, June 2004

   [SP67]   Barker, W. (NIST), "Recommendation for the Triple Data
            Encryption Algorithm (TDEA) Block Cipher", Special
            Publication 800-67, May 2004

   [Stal]   Stallings, W., "Local Networks", 1987, ISBN 0-02-415520-9.

   [Stei]   Steiner, J. et al, "Kerberos: An Authentication Service for
            Open Network Systems", in "Usenix Conference Proceedings",
            February 1988.

   [Weis]   Weissman, C., "Blacker: Security for the DDN: Examples of A1
            Security Engineering Trades", in "Symposium on Security and
            Privacy", IEEE Computer Society Press, May 1992, pp. 286-
            292.

   [X400]   International Telecommunications Union -- Telecommunication
            Standardization Sector (formerly "CCITT"), Recommendation
            X.400, "Message Handling Services: Message Handling System
            and Service Overview".

   [X419]   ---, "Message Handling Systems: Protocol Specifications",
            ITU-T Recommendation X.419. (Equivalent to ISO 10021-6).

   [X420]   ---, "Message Handling Systems: Interpersonal Messaging
            System", ITU-T Recommendation X.420. (Equivalent to ISO
            10021-7.).

   [X500]   ---, Recommendation X.500, "Information Technology -- Open
            Systems Interconnection -- The Directory: Overview of
            Concepts, Models, and Services". (Equivalent to ISO 9594-1.)

   [X501]   ---, Recommendation X.501, "Information Technology -- Open
            Systems Interconnection -- The Directory: Models".

   [X509]   ---, Recommendation X.509, "Information Technology -- Open
            Systems Interconnection -- The Directory: Authentication
            Framework", COM 7-250-E Revision 1, 23 February 2001.
            (Equivalent to ISO 9594-8.)

   [X519]   ---, Recommendation X.519, "Information Technology -- Open
            Systems Interconnection -- The Directory: Protocol
            Specifications".

   [X520]   ---, Recommendation X.520, "Information Technology -- Open
            Systems Interconnection -- The Directory: Selected Attribute
            Types".

   [X680]   ---, Recommendation X.680, "Information Technology --
            Abstract Syntax Notation One (ASN.1) -- Specification of
            Basic Notation", 15 November 1994. (Equivalent to ISO/IEC
            8824-1.)

   [X690]   ---, Recommendation X.690, "Information Technology -- ASN.1
            Encoding Rules -- Specification of Basic Encoding Rules
            (BER), Canonical Encoding Rules (CER) and Distinguished
            Encoding Rules (DER)", 15 November 1994. (Equivalent to
            ISO/IEC 8825-1.)

7. Acknowledgments

   George Huff had a good idea! [Huff]

Author's Address

   Dr. Robert W. Shirey
   3516 N. Kensington St.
   Arlington, Virginia  22207-1328
   USA

   EMail: rwshirey4949@verizon.net

Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78 and at www.rfc-editor.org/copyright.html, and
   except as set forth therein, the authors retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.

Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.