Network Working Group                                          R. Shirey
Request for Comments: 2828                        GTE / BBN Technologies
FYI: 36                                                         May 2000
Category: Informational

Internet Security Glossary

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

Abstract

   This Glossary (191 pages of definitions and 13 pages of references)
   provides abbreviations, explanations, and recommendations for use of
   information system security terminology. The intent is to improve the
   comprehensibility of writing that deals with Internet security,
   particularly Internet Standards documents (ISDs). To avoid confusion,
   ISDs should use the same term or definition whenever the same concept
   is mentioned. To improve international understanding, ISDs should use
   terms in their plainest, dictionary sense. ISDs should use terms
   established in standards documents and other well-founded
   publications and should avoid substituting private or newly made-up
   terms. ISDs should avoid terms that are proprietary or otherwise
   favor a particular vendor, or that create a bias toward a particular
   security technology or mechanism versus other, competing techniques
   that already exist or might be developed in the future.

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .   2
   2. Explanation of Paragraph Markings  . . . . . . . . . . . . . .   4
      2.1 Recommended Terms with an Internet Basis ("I") . . . . . .   4
      2.2 Recommended Terms with a Non-Internet Basis ("N")  . . . .   5
      2.3 Other Definitions ("O")  . . . . . . . . . . . . . . . . .   5
      2.4 Deprecated Terms, Definitions, and Uses ("D")  . . . . . .   6
      2.5 Commentary and Additional Guidance ("C") . . . . . . . . .   6
   3. Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 197
   5. Security Considerations  . . . . . . . . . . . . . . . . . . . 211
   6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 211
   7. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 211
   8. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 212

1. Introduction

   This Glossary provides an internally consistent, complementary set of
   abbreviations, definitions, explanations, and recommendations for use
   of terminology related to information system security. The intent of
   this Glossary is to improve the comprehensibility of Internet
   Standards documents (ISDs)--i.e., RFCs, Internet-Drafts, and other
   material produced as part of the Internet Standards Process [R2026]--
   and of all other Internet material, too. Some non-security terms are
   included to make the Glossary self-contained, but more complete lists
   of networking terms are available elsewhere [R1208, R1983].

   Some glossaries (e.g., [Raym]) list terms that are not listed here
   but could be applied to Internet security. However, those terms have
   not been included in this Glossary because they are not appropriate
   for ISDs.

   This Glossary marks terms and definitions as being either endorsed or
   deprecated for use in ISDs, but this Glossary is not an Internet
   standard. The key words "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
   and "OPTIONAL" are intended to be interpreted the same way as in an
   Internet Standard [R2119], but this guidance represents only the
   recommendations of this author. However, this Glossary includes
   reasons for the recommendations--particularly for the SHOULD NOTs--so
   that readers can judge for themselves whether to follow the
   recommendations.

   This Glossary supports the goals of the Internet Standards Process:

   o Clear, Concise, and Easily Understood Documentation

      This Glossary seeks to improve comprehensibility of security-
      related content of ISDs. 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, the
      terminology needs to be uniform across all ISDs; i.e., the same
      term or definition needs to be used whenever and wherever the same
      concept is mentioned. Harmonization of existing ISDs need not be
      done immediately, but it is desirable to correct and standardize
      the 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, ISDs should use terminology accurately, precisely,
      and unambiguously to enable Internet Standards to be implemented
      correctly.

   o Prior Implementation and Testing

      Just as STD protocols require demonstrated experience and
      stability before adoption, ISDs need to use well-established
      language. Using terms in their plainest, dictionary sense (when
      appropriate) helps to ensure international understanding. ISDs
      need to avoid using private, made-up terms in place of generally-
      accepted terms from standards and other publications. ISDs need to
      avoid substituting new definitions that conflict with established
      ones. ISDs need to avoid using "cute" synonyms (e.g., see: Green
      Book); no matter how popular a nickname may be in one community,
      it is likely to cause confusion in another.

   o Openness, Fairness, and Timeliness

      ISDs need to avoid terms that are proprietary or otherwise favor a
      particular vendor, or that create a bias toward 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 ISDs needs to be flexible and
      adaptable as the state of Internet security art evolves.

2. Explanation of Paragraph Markings

   Section 3 marks terms and definitions as follows:

   o Capitalization: Only terms that are proper nouns are capitalized.

   o Paragraph Marking: Definitions and explanations are stated in
      paragraphs that are marked as follows:

      - "I" identifies a RECOMMENDED Internet definition.
      - "N" identifies a RECOMMENDED non-Internet definition.
      - "O" identifies a definition that is not recommended as the first
        choice for Internet documents but is something that authors of
        Internet documents need to know.
      - "D" identifies a term or definition that SHOULD NOT be used in
        Internet documents.
      - "C" identifies commentary or additional usage guidance.

   The rest of Section 2 further explains these five markings.

2.1 Recommended Terms with an Internet Basis ("I")

   The paragraph marking "I" (as opposed to "O") indicates a definition
   that SHOULD be the first choice for use in ISDs. Most terms and
   definitions of this type MAY be used in ISDs; however, some "I"
   definitions are accompanied by a "D" paragraph that recommends
   against using the term. Also, some "I" definitions are preceded by an
   indication of a contextual usage limitation (e.g., see:
   certification), and ISDs should not the term and definition outside
   that context

   An "I" (as opposed to an "N") also indicates that the definition has
   an Internet basis. That is, either the Internet Standards Process is
   authoritative for the term, or the term is sufficiently generic that
   this Glossary can freely state a definition without contradicting a
   non-Internet authority (e.g., see: attack).

   Many terms with "I" definitions are proper nouns (e.g., see:
   Internet Protocol). For such terms, the "I" definition is intended
   only to provide basic information; the authoritative definition is
   found elsewhere.

   For a proper noun identified as an "Internet protocol", please refer
   to the current edition of "Internet Official Protocol Standards" (STD
   1) for the standardization state and status of the protocol.

2.2 Recommended Terms with a Non-Internet Basis ("N")

   The paragraph marking "N" (as opposed to "O") indicates a definition
   that SHOULD be the first choice for the term, if the term is used at
   all in Internet documents. Terms and definitions of this type MAY be
   used in Internet documents (e.g., see: X.509 public-key certificate).

   However, an "N" (as opposed to an "I") also indicates a definition
   that has a non-Internet basis or origin. Many such definitions are
   preceded by an indication of a contextual usage limitation, and this
   Glossary's endorsement does not apply outside that context.  Also,
   some contexts are rarely if ever expected to occur in a Internet
   document (e.g., see: 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.

   Many terms with "N" definitions are proper nouns (e.g., see:
   Computer Security Objects Register). For such terms, the "N"
   definition is intended only to provide basic information; the
   authoritative definition is found elsewhere.

2.3 Other Definitions ("O")

   The paragraph marking "O" indicates a definition that has a non-
   Internet basis, but indicates that the definition SHOULD NOT be used
   in ISDs *except* in cases where the term is specifically identified
   as non-Internet.

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

   For some terms that have a definition published by a non-Internet
   authority--government (see: object reuse), industry (see: Secure Data
   Exchange), national (see: Data Encryption Standard), or international
   (see: data confidentiality)--this Glossary marks the definition "N",
   recommending its use in Internet documents. In other cases, the non-
   Internet definition of a term is inadequate or inappropriate for
   ISDs. For example, it may be narrow or outdated, or it may need
   clarification by substituting more careful or more explanatory
   wording using other terms that are defined in this Glossary. In those
   cases, this Glossary marks the tern "O" and provides an "I"
   definition (or sometimes a different "N" definition), which precedes
   and supersedes the definition marked "O".

   In most of the cases where this Glossary provides a definition to
   supersede one from a non-Internet standard, the substitute is
   intended to subsume the meaning of the superseded "O" definition 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 OSI model and is inadequate for the full
   range of ISD usage; the "I" definition can be used in more situations
   and for more kinds of service. However, the "O" definition is also
   provided here so that ISD authors will be aware of the context in
   which the term is used more narrowly.

   When making substitutions, this Glossary attempts to use
   understandable English that does not contradict any non-Internet
   authority. Still, terminology differs between the standards of the
   American Bar Association, OSI, SET, the U.S. Department of Defense,
   and other authorities, and this Glossary probably is not exactly
   aligned with all of them.

2.4 Deprecated Terms, Definitions, and Uses ("D")

   If this Glossary recommends that a term or definition SHOULD NOT be
   used in ISDs, then either the definition has the paragraph marking
   "D", or the restriction is stated in a "D" paragraph that immediately
   follows the term or definition.

2.5 Commentary and Additional Guidance ("C")

   The paragraph marking "C" identifies text that is advisory or
   tutorial. This text MAY be reused in other Internet documents.  This
   text is not intended to be authoritative, but is provided to clarify
   the definitions and to enhance this Glossary so that Internet
   security novices can use it as a tutorial.

3. Definitions

   Note: Each acronym or other abbreviation (except items of common
   English usage, such as "e.g.", "etc.", "i.e.", "vol.", "pp.", "U.S.")
   that is used in this Glossary, either in a definition or as a subpart
   of a defined term, is also defined in this Glossary.

   $ 3DES
      See: triple DES.

   $ *-property
      (N) (Pronounced "star property".) See: "confinement property"
      under Bell-LaPadula Model.

   $ ABA Guidelines
      (N) "American Bar Association (ABA) Digital Signature Guidelines"
      [ABA], 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. [X680]

      (C) OSI standards use ASN.1 to specify data formats for protocols.
      OSI defines functionality in layers. Information objects at higher
      layers are abstractly defined to be implemented with objects at
      lower layers. A higher layer may define transfers of abstract
      objects between computers, and a lower layer may define transfers
      concretely as strings of bits. Syntax is needed to define abstract
      objects, and encoding rules are needed to transform between
      abstract objects and bit strings. (See: Basic Encoding Rules.)

      (C) 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
      See: access control center.

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

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

      (C) In this Glossary, "access" is intended to cover any ability to
      communicate with a system, including one-way communication in
      either direction. In actual practice, however, entities outside a
      security perimeter that can receive output from the system but
      cannot provide input or otherwise directly interact with the
      system, might be treated as not having "access" and, therefore, be
      exempt from security policy requirements, such as the need for a
      security clearance.

   $ access control
      (I) Protection of system resources against unauthorized access; a
      process by which use of system resources is regulated according to
      a security policy and is permitted by only authorized entities

      (users, programs, processes, or other systems) according to that
      policy. (See: access, access control service.)

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

   $ access control center (ACC)
      (I) A computer containing a database with entries that define a
      security policy for an access control service.

      (C) An ACC is sometimes used in conjunction with a key center to
      implement access control in a key distribution system for
      symmetric cryptography.

   $ access control list (ACL)
      (I) A mechanism that implements access control for a system
      resource by enumerating the identities of the system entities that
      are permitted to access the resource. (See: capability.)

   $ 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; in short, protection of system resources against
      unauthorized access. (See: access control, discretionary access
      control, identity-based security policy, mandatory access control,
      rule-based security policy.)

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

   $ access mode
      (I) A distinct type of data processing operation--e.g., read,
      write, append, or execute--that a subject can potentially perform
      on an object in a computer system.

   $ accountability
      (I) The property of a system (including all of its system
      resources) that ensures that the actions of a system entity may be
      traced uniquely to that entity, which can be held responsible for
      its actions. (See: audit service.)

      (C) Accountability permits detection and subsequent investigation
      of security breaches.

   $ accredit
   $ accreditation
      (I) An administrative declaration by a designated authority that
      an information system is approved to operate in a particular
      security configuration with a prescribed set of safeguards.
      [FP102] (See: certification.)

      (C) An accreditation is usually based on a technical certification
      of the system's security mechanisms. The terms "certification" and
      "accreditation" are used more in the U.S. Department of Defense
      and other government agencies than in commercial organizations.
      However, the concepts apply any place where managers are required
      to deal with and accept responsibility for security risks. The
      American Bar Association is developing accreditation criteria for
      CAs.

   $ ACL
      See: access control list.

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

      (O) "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]

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

   $ active wiretapping
      See: (secondary definition under) wiretapping.

   $ add-on security
      (I) "The retrofitting of protection mechanisms, implemented by
      hardware or software, after the [automatic data processing] system
      has become operational." [FP039]

   $ administrative security
      (I) Management procedures and constraints to prevent unauthorized
      access to a system. (See: security architecture.)

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

      (C) Examples include clear delineation and separation of duties,
      and configuration control.

   $ Advanced Encryption Standard (AES)
      (N) A future FIPS publication being developed by NIST to succeed
      DES. Intended to specify an unclassified, publicly-disclosed,
      symmetric encryption algorithm, available royalty-free worldwide.

   $ adversary
      (I) An entity that attacks, or is a threat to, a system.

   $ 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 individual items that comprise it.

   $ AH
      See: Authentication Header

   $ 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 deception.

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

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

   $ anonymous
      (I) The condition of having a name that is unknown or concealed.
      (See: anonymous login.)

      (C) 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 an account number. Parties to a transaction can thus
      remain relatively anonymous, but can also accept the transaction

      as legitimate. Real names of the parties cannot be easily
      determined by observers of the transaction, 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.

   $ anonymous login
      (I) An access control feature (or, rather, an access control
      weakness) in many Internet hosts that enables users to gain access
      to general-purpose or public services and resources on a host
      (such as allowing any user to transfer data using File Transfer
      Protocol) without having a pre-established, user-specific account
      (i.e., user name and secret password).

      (C) 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.

   $ APOP
      See: POP3 APOP.

   $ archive
       (I) (1.) 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. (See: backup.) (2.) Verb: To store data in such
      a way. (See: back up.)

      (C) 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
      (N) Advanced Research Projects Agency Network, a pioneer packet-
      switched network that was built in the early 1970s under contract
      to the U.S. Government, led to the development of today's
      Internet, and was decommissioned in June 1990.

   $ ASN.1
      See: Abstract Syntax Notation One.

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

   $ assurance
      (I) (1.) An attribute of an information system that provides
      grounds for having confidence that the system operates such that
      the system security policy is enforced. (2.) A procedure that
      ensures a system is developed and operated as intended by the
      system's security policy.

   $ assurance level
      (I) Evaluation usage: A specific level on a hierarchical scale
      representing successively increased confidence that a target of
      evaluation adequately fulfills the requirements. (E.g., see:
      TCSEC.)

   $ asymmetric cryptography
      (I) A modern branch of cryptography (popularly known as "public-
      key cryptography") in which the algorithms employ a pair of keys
      (a public key and a private key) and use a different component of
      the pair for different steps of the algorithm. (See: key pair.)

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

      (C) For encryption: In an asymmetric encryption algorithm (e.g.,
      see: 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.

      (C) For signature: In an asymmetric digital signature algorithm
      (e.g., see: 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.

      (C) For key agreement: In an asymmetric key agreement algorithm
      (e.g., see: Diffie-Hellman), Alice and Bob each send their own
      public key to the other person. Then each uses their own private
      key and the other's public key to compute the new key value.

   $ attack
      (I) An assault on system security that derives from an intelligent
      threat, i.e., an intelligent act that is a deliberate attempt
      (especially in the sense of a method or technique) to evade
      security services and violate the security policy of a system.
      (See: penetration, violation, vulnerability.)

       - Active vs. passive: An "active attack" attempts to alter system
         resources or affect their operation. A "passive attack"
         attempts to learn or make use of information from the system
         but does not affect system resources. (E.g., see: wiretapping.)

       - Insider vs. outsider: An "inside attack" is an attack 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 those who granted the
         authorization. An "outside attack" is initiated from outside
         the 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.

      (C) 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  |
      + - - - - - - - - - - - - +  + - - - - +  + - - - - - - - - - - -+

   $ attribute authority
      (I) A CA that issues attribute certificates.

      (O) "An authority, trusted by the verifier to delegate privilege,
      which issues attribute certificates." [FPDAM]

   $ attribute certificate
      (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. [X509]

      (O) "A set of attributes of a user together with some other
      information, rendered unforgeable by the digital signature created
      using the private key of the CA which issued it." [X509]

      (O) "A data structure that includes some attribute values and
      identification information about the owner of the attribute
      certificate, all digitally signed by an Attribute Authority. This
      authority's signature serves as the guarantee of the binding
      between the attributes and their owner." [FPDAM]

      (C) A public-key certificate binds a subject name to a public key
      value, along with information needed to perform certain
      cryptographic functions. 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.

      (C) 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 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
      See: security audit trail.

   $ AUTH
      See: POP3 AUTH.

   $ authentic signature
      (I) A signature (particularly a digital signature) that can be
      trusted because it can be verified. (See: validate vs. verify.)

   $ authenticate
      (I) Verify (i.e., establish the truth of) an identity claimed by
      or for a system entity. (See: authentication.)

      (D) In general English usage, this term usually means "to prove
      genuine" (e.g., an art expert authenticates a Michelangelo
      painting). But the recommended definition carries a much narrower
      meaning. For example, to be precise, an ISD SHOULD NOT say "the
      host authenticates each received datagram". Instead, the ISD
      SHOULD say "the host authenticates the origin of each received
      datagram". In most cases, we also can say "and verifies the
      datagram's integrity", because that is usually implied. (See:
      ("relationship between data integrity service and authentication
      services" under) data integrity service.)

      (D) ISDs SHOULD NOT talk about authenticating a digital signature
      or digital certificate. Instead, we "sign" and then "verify"
      digital signatures, and we "issue" and then "validate" digital
      certificates. (See: validate vs. verify.)

   $ authentication
      (I) The process of verifying an identity claimed by or for a
      system entity. (See: authenticate, authentication exchange,
      authentication information, credential, data origin
      authentication, peer entity authentication.)

      (C) An authentication process consists of two steps:

      1. Identification step: Presenting an identifier to the security
         system. (Identifiers should be assigned carefully, because
         authenticated identities are the basis for other security
         services, such as access control service.)

      2. Verification step: Presenting or generating authentication
         information that corroborates the binding between the entity
         and the identifier. (See: verification.)

      (C) See: ("relationship between data integrity service and
      authentication services" under) data integrity service.

   $ authentication code
      (D) ISDs SHOULD NOT use this term as a synonym for any form of
      checksum, whether cryptographic or not. The word "authentication"
      is misleading because the mechanism involved usually serves a data
      integrity function rather than an authentication function, and the
      word "code" is misleading because it implies that either encoding
      or encryption is involved or that the term refers to computer
      software. (See: message authentication code.)

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

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

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

      (C) Replay protection may be selected by the receiver when a
      security association is established. AH authenticates upper-layer
      protocol data units and as much of 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.

      (C) AH may be used alone, or in combination with the IPsec ESP
      protocol, 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 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.)

      (C) Authentication information may exist as, or be derived from,
      one of the following:

       - Something the entity knows. (See: password).
       - Something the entity possesses. (See: token.)
       - 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.)

      (C) 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) "An entity, responsible for the issuance of certificates."
      [FPDAM]

      (C) ISDs SHOULD NOT use this term as a synonym for AA, CA, RA,
      ORA, or similar terms, because it may cause confusion. Instead,
      use the full term at the first instance of usage and then, if it
      is necessary to shorten text, use the style of abbreviation
      defined in this Glossary.

      (C) ISDs SHOULD NOT use this definition for any PKI entity,
      because the definition is ambiguous with regard to whether the
      entity actually issues certificates (e.g., attribute authority or
      certification authority) or just has accountability for processes
      that precede or follow signing (e.g., registration authority).
      (See: issue.)

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

      (C) ISDs SHOULD NOT use this term or definition because they are
      ambiguous with regard to which specific types of PKI entities they
      address.

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

      (O) "A revocation list containing a list of public-key
      certificates issued to authorities, which are no longer considered
      valid by the certificate issuer." [FPDAM]

   $ authorization
   $ authorize
      (I) (1.) An "authorization" is a right or a permission that is
      granted to a system entity to access a system resource. (2.) An
      "authorization process" is a procedure for granting such rights.
      (3.) To "authorize" means to grant such a right or permission.
      (See: privilege.)

      (O) SET usage: "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]

   $ automated information system
      (I) An organized assembly of resources and procedures--i.e.,
      computing and communications equipment and services, with their
      supporting facilities and personnel--that collect, record,
      process, store, transport, retrieve, or display information to
      accomplish a specified set of functions.

   $ availability
      (I) The property of a system or a system resource being accessible
      and usable 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,
      reliability, survivability.)

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

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

      (C) 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.

   $ back door
      (I) A hardware or software mechanism that (a) provides access to a
      system and its resources by other than the usual procedure, (b)
      was deliberately left in place by the system's designers or
      maintainers, and (c) usually is not publicly known. (See: trap
      door.)

      (C) For example, a way to access a computer other than through a
      normal login. Such access paths do not necessarily have malicious
      intent; e.g., operating systems sometimes are shipped by the
      manufacturer with privileged accounts intended for use by field
      service technicians or the vendor's maintenance programmers. (See:
      trap door.)

   $ back up vs. backup
      (I) Verb "back up": To store data for the purpose of creating a
      backup copy. (See: archive.)

      (I) Noun/adjective "backup": (1.) A reserve copy of data that is
      stored separately from the original, for use if the original
      becomes lost or damaged. (See: archive.) (2.) Alternate means to
      permit performance of system functions despite a disaster to
      system resources. (See: contingency plan.)

   $ baggage
      (D) ISDs SHOULD NOT use this term to describe a data element
      except when stated as "SET(trademark) baggage" with the following
      meaning:

      (O) SET usage: 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]

   $ bandwidth
      (I) Commonly used to mean the capacity of a communication channel
      to pass data through the channel in a given amount of time.
      Usually expressed in bits per second.

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

      (O) SET usage: 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.)

   $ 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 hosts) in the network that can be directly
      accessed from networks on the other side of the firewall.

      (C) 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.

   $ BCA
      See: brand certification authority.

   $ BCI
      See: brand CRL identifier.

   $ Bell-LaPadula Model
      (N) A formal, mathematical, state-transition model of security
      policy for multilevel-secure computer systems. [Bell]

      (C) The model separates computer system elements into a set of
      subjects and a set of 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.

      (C) In this model, a multilevel-secure system satisfies several
      rules, including the following:

       - "Confinement property" (also called "*-property", pronounced
         "star property"): A subject has write access to an object only
         if classification of the object dominates the clearance of the
         subject.

       - "Simple security property": A subject has read access to an
         object only if the clearance of the subject dominates the
         classification of the object.

       - "Tranquillity property": The classification of an object does
         not change while the object is being processed by the system.

   $ BER
      See: Basic Encoding Rules.

   $ beyond A1
      (O) (1.) Formally, a level of security assurance that is beyond
      the highest level of criteria specified by the TCSEC. (2.)
      Informally, a level of trust so high that it cannot be provided or
      verified by currently available assurance methods, and
      particularly not by currently available formal methods.

   $ BIN
      See: bank identification number.

   $ bind
      (I) To inseparably associate by applying some mechanism, such as
      when a CA uses a digital signature to bind together a subject and
      a public key in a public-key certificate.

   $ biometric authentication
      (I) A method of generating authentication information for a person
      by digitizing measurements of a physical characteristic, such as a
      fingerprint, a hand shape, a retina pattern, a speech pattern
      (voiceprint), or handwriting.

   $ bit
      (I) The smallest unit of information storage; a contraction of the
      term "binary digit"; one of two symbols--"0" (zero) and "1" (one)
      --that are used to represent binary numbers.

   $ BLACK
      (I) Designation for information system equipment or facilities
      that handle (and for data that contains) only ciphertext (or,
      depending on the context, only unclassified information), and for
      such data itself. This term derives from U.S. Government COMSEC
      terminology. (See: RED, RED/BLACK separation.)

   $ block cipher
      (I) An encryption algorithm that breaks plaintext into fixed-size
      segments and uses the same key to transform each plaintext segment
      into a fixed-size segment of ciphertext. (See: mode, stream
      cipher.)

      (C) For example, Blowfish, DEA, IDEA, RC2, and SKIPJACK. However,
      a block cipher can be adapted to have a different external
      interface, such as that of a stream cipher, by using a mode of
      operation to "package" the basic algorithm.

   $ 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]

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

      (O) SET usage: The name of a payment card. 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 usage: 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 usage: 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) Cryptographic usage: 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. (This term applies to encrypted
      data or, more generally, to a cryptographic algorithm or
      cryptographic system.)

   $ bridge
      (I) A computer that is a gateway between two networks (usually two
      LANs) at OSI layer 2. (See: router.)

   $ British Standard 7799
      (N) Part 1 is a standard code of practice and provides guidance on
      how to secure an information system. Part 2 specifies the
      management framework, objectives, and control requirements for
      information security management systems [B7799]. The certification
      scheme works like ISO 9000. It is in use in the UK, the
      Netherlands, Australia, and New Zealand and might be proposed as
      an ISO standard or adapted to be part of the Common Criteria.

   $ browser
      (I) An client computer program that can retrieve and display
      information from servers on the World Wide Web.

      (C) For example, Netscape's Navigator and Communicator, and
      Microsoft's Explorer.

   $ brute force
      (I) A cryptanalysis technique or other kind of attack method
      involving an exhaustive procedure that tries all possibilities,
      one-by-one.

      (C) For example, for ciphertext where the analyst already knows
      the decryption algorithm, a brute force technique to finding the
      original plaintext is to decrypt the message with every possible
      key.

   $ BS7799
      See: British Standard 7799.

   $ 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.
      (See: octet.)

      (C) Larger than a "bit", but smaller than a "word". Although
      "byte" almost always means "octet" today, bytes had other sizes
      (e.g., six bits, nine bits) in earlier computer architectures.

   $ CA
      See: certification authority.

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

      (C) That is, a digital certificate whose holder is able to issue
      digital certificates. 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."

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

   $ capability
      (I) A token, usually an unforgeable data value (sometimes called a
      "ticket") 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 named or indicated by the token. (See: access control
      list, credential, digital certificate.)

      (C) This concept can be implemented as a digital certificate.
      (See: attribute certificate.)

   $ CAPI
      See: cryptographic application programming interface.

   $ CAPSTONE chip
      (N) An integrated circuit (the Mykotronx, Inc. MYK-82) with a Type
      II cryptographic processor that implements SKIPJACK, KEA, DSA,
      SHA, and basic mathematical functions to support asymmetric
      cryptography, and includes the key escrow feature of the CLIPPER
      chip. (See: FORTEZZA card.)

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

   $ card backup
      See: token backup.

   $ card copy
      See: token copy.

   $ card restore
      See: token restore.

   $ cardholder
      (I) An entity that has been issued a card.

      (O) SET usage: "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 usage: 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 usage: 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 C.A. (Carlisle Adams)
      and S.T. (Stafford Tavares). [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: compartment.)

   $ CAW
      See: certification authority workstation.

   $ CBC
      See: cipher block chaining.

   $ CCA
      See: cardholder certification authority.

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

   $ CERT
      See: computer emergency response team.

   $ certificate
      (I) General English usage: A document that attests to the truth of
      something or the ownership of something.

      (C) Security usage: See: capability, digital certificate.

      (C) PKI usage: See: attribute certificate, public-key certificate.

   $ certificate authority
      (D) ISDs SHOULD NOT use this term because it looks like sloppy use
      of "certification authority", which is the term standardized by
      X.509.

   $ certificate chain
      (D) ISDs SHOULD NOT use this term because it duplicates the
      meaning of a standardized term. Instead, use "certification path".

   $ certificate chain validation
      (D) ISDs SHOULD NOT use this term because 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, validity period.)

   $ certificate extension
      See: extension.

   $ certificate holder
      (D) ISDs SHOULD NOT use this term as a synonym for the subject of
      a digital certificate because the term is potentially ambiguous.
      For example, the term could also refer to a system entity, such as
      a repository, that simply has possession of a copy of the
      certificate. (See: certificate owner.)

   $ certificate management
      (I) The functions that a CA may perform during the life cycle 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 owner
      (D) ISDs SHOULD NOT use this term as a synonym for the subject of
      a digital certificate because the term is potentially ambiguous.
      For example, the term could also refer to a system entity, such as
      a corporation, that has acquired a certificate to operate some
      other entity, such as a Web server. (See: certificate holder.)

   $ 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] (See: certification
      practice statement.)

      (C) A certificate policy can help a certificate user 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 goods within a given price range." [R2527]

      (C) 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.

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

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

      (C) 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".

      (O) MISSI usage: To rekey a MISSI X.509 public-key certificate
      means that the issuing authority creates a new certificate that is
      identical to the old one, except the new one has a new, different
      KEA key; or a new, different DSS key; or 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 data binding
      asserted by an existing public-key certificate is extended in time
      by issuing a new certificate. (See: certificate rekey, certificate
      update.)

      (C) 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) ISDs SHOULD NOT use this term because it looks like imprecise
      use of a term standardized by PKCS #10 and used in PKIX. Instead,
      use the standard term, "certification request".

   $ 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 a revocation date.

      (C) 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 before certificate
      expiration.

   $ certificate revocation list (CRL)
      (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, X.509
      certificate revocation list.)

      (O) "A signed list indicating a set of certificates that are no
      longer considered valid by the certificate issuer. After a
      certificate appears on a CRL, it is deleted from a subsequent CRL
      after the certificate's expiry. CRLs may be used to identify
      revoked public-key certificates or attribute certificates and may
      represent revocation of certificates issued to authorities or to
      users. The term CRL is also commonly used as a generic term
      applying to all the different types of revocation lists, including
      CRLs, ARLs, ACRLs, etc." [FPDAM]

   $ certificate revocation tree
      (I) A mechanism for distributing notice 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
      (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.

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

   $ certificate status responder
      (N) FPKI usage: A trusted on-line server that acts for a CA to
      provide authenticated certificate status information to
      certificate users. [FPKI] Offers an alternative to issuing a CRL,
      but is not supported in X.509. (See: certificate revocation tree.)

   $ 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.)

      (C) 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
      (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.)

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

      (C) The system entity may be a human being or an organization, or
      a device or process under the control of a human or an
      organization.

      (D) ISDs SHOULD NOT use this term as a synonym for the "subject"
      of a certificate.

   $ certificate validation
      (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.)

      (O) "The process of ensuring that a certificate is valid including
      possibly the construction and processing of a certification path,
      and ensuring that all certificates in that path have not expired
      or been revoked." [FPDAM]

      (C) To validate a certificate, a certificate user checks that the
      certificate is properly formed and signed and currently in force:

       - Checks the signature: Employs 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 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 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. (CRLs themselves require
         a similar validation process.)

   $ certification
      (I) Information system usage: Technical evaluation (usually made
      in support of an accreditation action) of an information system's
      security features and other safeguards to establish the extent to
      which the system's design and implementation meet specified
      security requirements. [FP102] (See: accreditation.)

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

      (I) Public key usage: 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. In addition to binding a key to a name, a
      public-key certificate may bind those items to other restrictive
      or explanatory data items. (See: X.509 public-key certificate.)

      (O) SET usage: "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)
      (I) An entity that issues digital certificates (especially X.509
      certificates) and vouches for the binding between the data items
      in a certificate.

      (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]

      (C) Certificate users depend on the validity of information
      provided by a certificate. Thus, a CA should be someone that
      certificate users trust, and 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 life cycle of key pairs associated with the
      certificates (see: key management).

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

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

      (C) 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 of the hierarchy issue certificates only to non-CA
      entities, called "end 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.

      (O) MISSI usage: A MISSI certification hierarchy 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".

      (O) PEM usage: A PEM certification hierarchy 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".

      (O) SET usage: A SET certification hierarchy 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
      (I) An ordered sequence of public-key certificates (or a sequence
      of public-key certificates followed by 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
      a certified public key (or certified attributes) of the entity
      that is the subject of that last certificate. (See: certificate
      validation, valid certificate.)

      (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." [X509, R2527]

      (C) The path is the "list of certificates needed to allow a
      particular user to obtain the public key of another." [X509] The
      list is "linked" in the sense that the digital signature of each
      certificate (except 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 owned by the entity that
      signed.

      (C) In the X.509 quotation in the previous "C" paragraph, 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
      should be a trusted certificate (it might be a root certificate)
      or the signature on the first certificate should be verified by a
      trusted key (it might be a root key), but such trust is defined
      relative to each user, not absolutely for all users.

   $ certification policy
      (D) ISDs SHOULD NOT use this term. 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." [ABA96, R2527] (See: certificate
      policy.)

      (C) 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 employs 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. [ABA]

      (C) 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 a single CPS may support multiple
      certificate policies, which may be used for different application
      purposes or by different user communities. Multiple CAs, each with
      a different CPS, may support the same certificate policy. [R2527]

   $ certification request
      (I) A algorithm-independent transaction format, defined by PCKS
      #10 and used in PKIX, that contains a DN, a public key, and
      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.,
      see: X.509 public key certificate), such as the identity of the
      certificate's subject and the ownership of a public key. (See:
      certification.)

      (C) 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 employs measures to verify the truth,
      accuracy, and binding between data items in a digital certificate.

      (C) A description of the measures used for verification should be
      included in the CA's CPS.

   $ CFB
      See: cipher feedback.

   $ Challenge Handshake Authentication Protocol (CHAP)
      (I) A peer entity authentication method for PPP, using a randomly-
      generated challenge and requiring a matching response that depends
      on a cryptographic hash 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.

   $ Challenge-Response Authentication Mechanism (CRAM)
      (I) IMAP4 usage: 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.)

      (C) The server includes a unique timestamp 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 timestamp with a shared secret that is known only to the
      client and the server.

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

   $ CHAP
      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 the purpose of detecting changes in
      the data. (See: cyclic redundancy check, data integrity service,
      error detection code, hash, keyed hash, protected checksum.)

      (C) To gain confidence that a data object has not been changed, an
      entity that later uses the data can compute a checksum and compare
      it with the checksum that was stored or transmitted with the
      object.

      (C) Computer systems and networks employ 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).

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

   $ CIAC
      See: Computer Incident Advisory Capability.

   $ CIK
      See: cryptographic ignition key.

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

   $ cipher block chaining (CBC)
      (I) An block cipher mode that enhances electronic codebook mode by
      chaining together blocks of ciphertext it produces. [FP081] (See:
      [R1829], [R2451].)

      (C) 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)
      (I) An block cipher mode that enhances electronic code book mode
      by chaining together the blocks of ciphertext it produces and
      operating on plaintext segments of variable length less than or
      equal to the block length. [FP081]

      (C) This mode operates by using the previously generated
      ciphertext segment as the algorithm's input (i.e., by "feeding
      back" the ciphertext) 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.

   $ ciphertext
      (I) 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: cleartext, plaintext.)

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

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

   $ CIPSO
      See: Common IP Security Option.

   $ CKL
      See: compromised key list.

   $ class 2, 3, 4, or 5
      (O) U.S. Department of Defense usage: Levels of PKI assurance
      based on risk and value of information to be protected [DOD3]:

       - Class 2: For handling low-value information (unclassified, not
         mission-critical, or low monetary value) or protection of
         system-high information in low- to medium-risk environment.

       - Class 3: For handling medium-value information in low- to
         medium-risk environment. Typically requires identification of a
         system entity as a legal person, rather than merely a member of
         an organization.

       - Class 4: For handling medium- to high-value information in any
         environment. Typically requires identification of an entity as
         a legal person, rather than merely a member of an organization,
         and a cryptographic hardware token for protection of keying
         material.

       - Class 5: For handling high-value information in a high-risk
         environment.

   $ classification
   $ classification level
      (I) (1.) A grouping of classified information to which a
      hierarchical, restrictive security label is applied to increase
      protection of the data. (2.) The level of protection that is
      required to be applied to that information. (See: security level.)

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

      (C) The term is mainly used in government, especially in the
      military, although the concept underlying the term also applies
      outside government. In the U.S. Department of Defense, for
      example, it means information that has been determined pursuant to
      Executive Order 12958 ("Classified National Security Information",
      20 April 1995) or any predecessor order to require protection
      against unauthorized disclosure and is marked to indicate its
      classified status when in documentary form.

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

      (C) A clean system is not necessarily in a secure state.

   $ clearance
      See: security clearance.

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

   $ cleartext
      (I) Data in which the semantic information content (i.e., the
      meaning) is intelligible or is directly available. (See:
      plaintext.)

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

      (D) ISDs SHOULD NOT use this term as a synonym for "plaintext",
      the input to an encryption operation, because the plaintext input
      to encryption may itself be ciphertext that was output from
      another operation. (See: superencryption.)

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

      (C) Usually, the requesting entity is a computer process, and it
      makes the request on behalf of a human user. In some cases, the
      server may itself be a client of some other server.

   $ CLIPPER chip
      (N) The Mykotronx, Inc. MYK-82, an integrated microcircuit with a
      cryptographic processor that implements the SKIPJACK encryption
      algorithm and supports key escrow. (See: CAPSTONE, Escrowed
      Encryption Standard.)

      (C) The key escrow scheme for a chip involves a SKIPJACK key
      common to all chips 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. Department of Defense usage: 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: open security environment.)

   $ code
      (I) noun: A system of symbols used to represent information, which
      might originally have some other representation. (See: encode.)

      (D) ISDs SHOULD NOT use this term as synonym for the following:
      (a) "cipher", "hash", or other words that mean "a cryptographic
      algorithm"; (b) "ciphertext"; or (c) "encrypt", "hash", or other
      words that refer to applying a cryptographic algorithm.

      (D) ISDs SHOULD NOT this word as an abbreviation for the following
      terms: country code, cyclic redundancy code, Data Authentication
      Code, error detection code, Message Authentication Code, object
      code, or source code. To avoid misunderstanding, use the fully
      qualified term, at least at the point of first usage.

   $ color change
      (I) In a system that is 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.

   $ Common Criteria
   $ Common Criteria for Information Technology Security
      (N) "The Common Criteria" is a standard for evaluating information
      technology products and systems, such as operating systems,
      computer networks, distributed systems, and applications. It
      states requirements for security functions and for assurance
      measures. [CCIB]

      (C) 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" (FC)
      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 2.1 of the Criteria is equivalent to ISO's
      International Standard 15408 [I15408]. The U.S. Government intends
      that this standard eventually will supersede both the TCSEC and
      FIPS PUB 140-1. (See: NIAP.)

      (C) 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.

   $ Common IP Security Option (CIPSO)
      See: (secondary definition under) Internet Protocol Security
      Option.

   $ common name
      (I) 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.)

      (C) For example, "Dr. E. F. Moore", "The United Nations", or
      "12-th Floor Laser Printer".

   $ 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.

      (C) Usually understood to include cryptographic algorithms and key
      management methods and processes, devices that implement them, and
      the life cycle management of keying material and devices.

   $ community string
      (I) A community name in the form of an octet string that serves as
      a cleartext password in SNMP version 1. [R1157]

   $ compartment
      (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: category.)

      (C) The term is usually understood to include the special handling
      procedures to be used for the information.

   $ compromise
      See: data compromise, security compromise.

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

      (C) A CKL is issued by an 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
      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.)

      (C) For example, the CERT Coordination Center at Carnegie-Mellon
      University (sometimes called "the" CERT) and the Computer Incident
      Advisory Capability.

   $ Computer Incident Advisory Capability (CIAC)
      (N) A computer emergency response team in the U.S. Department of
      Energy.

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

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

      (C) Usually understood to include functions, features, and
      technical characteristics of computer hardware and software,
      especially operating systems.

   $ 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.)

      (C) To be considered a CSIRT, an organization must do as follows:

       - Provide a (secure) channel for receiving reports about
         suspected security incidents.
       - Provide assistance to members of its constituency in handling
         the incidents.
       - 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 elements 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.

      (C) 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) gov(101)
      csor(3)}.

   $ COMSEC
      See: communication security.

   $ confidentiality
      See: data confidentiality.

   $ 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.)

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

   $ confinement property
      See: (secondary definition under) Bell-LaPadula Model.

   $ connectionless data integrity service
      (I) A security service that provides data integrity service for an
      individual IP datagram, by detecting modification of the datagram,
      without regard to the ordering of the datagram in a stream of
      datagrams.

      (C) A connection-oriented data integrity service would be able to
      detect lost or reordered datagrams within a stream of datagrams.

   $ 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.)

   $ controlled security mode
      (D) ISDs SHOULD NOT use this term. It was defined in an earlier
      version of the U.S. Department of Defense policy that regulates
      system accreditation, but was subsumed by "partitioned security
      mode" in the current version. [DOD2]

      (C) The term refers to a mode of operation of an information
      system, wherein at least some users with access to the system have
      neither a security clearance nor a need-to-know for all classified
      material contained in the system. However, separation and control
      of users and classified material on the basis, respectively, of
      clearance and classification level are not essentially under
      operating system control like they are in "multilevel security
      mode".

      (C) Controlled mode was intended to encourage ingenuity in meeting
      the security requirements of Defense policy 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 the true "multilevel security mode". This was 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 permitted concurrent access to the
      system.

   $ cookie
      (I) access control usage: A synonym for "capability" or "ticket"
      in an access control system.

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

      (I) HTTP usage: 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.

      (C) 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.

   $ 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.)

   $ copy
      See: card copy.

   $ correctness integrity
      (I) Accuracy and consistency of the information that data values
      represent, rather than of the data itself. Closely related to
      issues of accountability and error handling. (See: data integrity,
      source integrity.)

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

   $ countermeasure
      (I) An action, device, procedure, or technique that reduces 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.

      (C) In an Internet protocol, a countermeasure may take the form of
      a protocol feature, an element function, or a usage constraint.

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

      (C) 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.

   $ covert channel
      (I) A intra-system channel that permits two cooperating entities,
      without exceeding their access authorizations, to transfer
      information in a way that violates the system's security policy.
      (See: channel, out of band.)

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

      (C) 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:

       - "Timing channel": A system feature that enable 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.

       - "Storage channel": 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.

   $ CPS
      See: certification practice statement.

   $ cracker
      (I) Someone who tries to break the security of, and gain access
      to, someone else's system without being invited to do so. (See:
      hacker and intruder.)

   $ CRAM
      See: Challenge-Response Authentication Mechanism.

   $ CRC
      See: cyclic redundancy check.

   $ credential(s)
      (I) Data that is transferred or presented to establish either a
      claimed identity or the authorizations of a system entity. (See:
      authentication information, capability, ticket.)

      (O) "Data that is transferred to establish the claimed identity of
      an entity." [I7498 Part 2]

   $ critical
      1. (I) "Critical" system resource: A condition of a service or
      other system resource such that denial of access to (i.e., 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. (See: availability, sensitive.)

      2. (N) "Critical" extension: Each extension of an X.509
      certificate (or CRL) is marked as being either critical or non-
      critical. If an extension is critical and a certificate user (or
      CRL user) does not recognize the extension type or does not
      implement its semantics, then the user is required to treat the
      certificate (or CRL) as invalid. If an extension is non-critical,
      a user that does not recognize or implement that extension type is
      permitted to ignore the extension and process the rest of the
      certificate (or CRL).

   $ CRL
      See: certificate revocation list.

   $ CRL distribution point
      See: distribution point.

   $ CRL extension
      See: extension.

   $ cross-certificate
      See: cross-certification.

   $ cross-certification
      (I) The act or process by which two CAs each certify a public key
      of the other, issuing a public-key certificate to that other CA.

      (C) Cross-certification enables users to validate each other's
      certificate when the users are certified under different
      certification hierarchies.

   $ cryptanalysis
      (I) The mathematical science that deals with analysis of a
      cryptographic system in order to gain knowledge needed to break or
      circumvent the protection that the system is designed to provide.
      (See: cryptology.)

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

      (C) The "O" definition states the traditional goal of
      cryptanalysis--convert the ciphertext to plaintext (which usually
      is cleartext) 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
      the "I" definition reflects that. In all cases, however, a
      cryptanalyst tries to uncover or reproduce someone else's
      sensitive data, such as cleartext, 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
      (D) Except as part of certain long-established terms listed in
      this Glossary, ISDs SHOULD NOT use this abbreviated term because
      it may be misunderstood. Instead, use "cryptography" or
      "cryptographic".

   $ cryptographic algorithm
      (I) An algorithm that employs the science of cryptography,
      including encryption algorithms, cryptographic hash algorithms,
      digital signature algorithms, and 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. For
      example, see: PKCS #11, [R2628].

   $ 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
      See: (secondary definition under) hash function.

   $ cryptographic ignition key (CIK)
      (I) A physical (usually electronic) token used to store,
      transport, and protect cryptographic keys. (Sometimes abbreviated
      as "crypto ignition key".)

      (C) A typical use is to divide a split key between a CIK and a
      cryptographic module, so that it is necessary to combine the two
      to regenerate a key-encrypting key and thus activate the module
      and other keys it contains.

   $ cryptographic key
      (I) Usually shortened to just "key". An input parameter that
      varies the transformation performed by a cryptographic algorithm.

      (O) "A sequence of symbols that controls the operations of
      encipherment and decipherment." [I7498 Part 2]

      (C) If a key value needs to be kept secret, the sequence of
      symbols (usually bits) that comprise it should be random, or at
      least pseudo-random, because that makes the key hard for an
      adversary to guess. (See: cryptanalysis, brute force attack.)

   $ Cryptographic Message Syntax (CMS)
      (I) A encapsulation syntax for digital signatures, hashes, and
      encryption of arbitrary messages. [R2630]

      (C) CMS was derived 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
      (I) A set of cryptographic algorithms together with the key
      management processes that support use of the algorithms in some
      application context.

      (C) This "I" definition covers a wider range of algorithms than
      the following "O" definition:

      (O) "A collection of transformations from plaintext into
      ciphertext 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
      (I) A portable, user-controlled, physical device used to store
      cryptographic information and possibly perform cryptographic
      functions. (See: cryptographic card, token.)

      (C) A smart token may implement some set of cryptographic
      algorithms and may implement related algorithms and 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
      (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.)

      (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 Part 2]

   $ Cryptoki
      See: (secondary definition under) PKCS #11.

   $ cryptology
      (I) The science that includes both cryptography and cryptanalysis,
      and sometimes is said to include steganography.

   $ cryptonet
      (I) A group of system entities that share a secret cryptographic
      key for a symmetric algorithm.

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

      (C) 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 cryptanalysis.

      (C) Although we deprecate its prefix, this term is long-
      established in COMPUSEC usage. (See: crypto) In the context of
      certificates and public keys, "key lifetime" and "validity period"
      are often used instead.

   $ cryptosystem
      (D) ISDs SHOULD NOT use this term as an abbreviation for
      cryptographic system. (For rationale, see: crypto.)

   $ CSIRT
      See: computer security incident response team.

   $ CSOR
      See: Computer Security Objects Register.

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

   $ cyclic redundancy check (CRC)
      (I) Sometimes called "cyclic redundancy code". 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.

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

   $ DASS
      See: Distributed Authentication Security Service.

   $ data
      (I) Information in a specific physical representation, usually a
      sequence of symbols that have meaning; especially a representation
      of information that can be processed or produced by a computer.

   $ Data Authentication Algorithm
      (N) A keyed hash function equivalent to DES cipher block chaining
      with IV = 0. [A9009]

      (D) ISDs SHOULD NOT use the uncapitalized form of this term as a
      synonym for other kinds of checksums.

   $ data authentication code vs. Data Authentication Code (DAC)
      1. (N) Capitalized: "The Data Authentication Code" refers to a
      U.S. Government standard [FP113] for a checksum that is computed
      by the Data Authentication Algorithm. (Also known as the ANSI
      standard Message Authentication Code [A9009].)

      2. (D) Not capitalized: ISDs SHOULD NOT use "data authentication
      code" as a synonym for another kind of checksum, because this term
      mixes concepts in a potentially misleading way. (See:
      authentication code.) Instead, use "checksum", "error detection
      code", "hash", "keyed hash", "Message Authentication Code", or
      "protected checksum", depending on what is meant.

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

   $ data confidentiality
      (I) "The property that information is not made available or
      disclosed to unauthorized individuals, entities, or processes
      [i.e., to any unauthorized system entity]." [I7498 Part 2]. (See:
      data confidentiality service.)

      (D) ISDs SHOULD NOT use this term as a synonym for "privacy",
      which is a different concept.

   $ data confidentiality service
      (I) A security service that protects data against unauthorized
      disclosure. (See: data confidentiality.)

      (D) ISDs 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 as part of the U.S.
      Government's Data Encryption Standard. 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: DES,
      symmetric cryptography.)

      (C) 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.
      (See: key-encrypting key.)

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

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

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

      (C) Deals with constancy of and confidence in data values, not
      with the information that the values represent (see: correctness
      integrity) or 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.)

      (C) 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.

      (C) 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 Part 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.)

      (C) 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.

      (C) 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.

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

   $ data privacy
      (D) ISDs SHOULD NOT use this term because it mix concepts in a
      potentially misleading way. Instead, use either "data
      confidentiality" or "privacy", depending on what is meant.

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

      (C) Both data confidentiality service and data integrity service
      are needed to achieve data security.

   $ datagram
      (I) "A self-contained, independent entity of data carrying
      sufficient information to be routed from the source to the
      destination." [R1983]

   $ DEA
      See: Data Encryption Algorithm.

   $ deception
      See: (secondary definition under) threat consequence.

   $ decipher
      (D) ISDs SHOULD NOT use this term as a synonym for "decrypt",
      except in special circumstances. (See: (usage discussion under)
      encryption.)

   $ decipherment
      (D) ISDs SHOULD NOT use this term as a synonym for "decryption",
      except in special circumstances. (See: (usage discussion under)
      encryption.)

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

      (D) ISDs SHOULD NOT use this term as a synonym for "decrypt",
      because that would mix concepts in a potentially misleading way.

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

   $ decryption
      See: (secondary definition under) encryption.

   $ dedicated security mode
      (I) A mode of operation of an information system, wherein all
      users have the clearance or authorization, and the need-to-know,
      for all data handled by the system. In this mode, the system may
      handle either a single classification level or category of
      information or a range of levels and categories. [DOD2]

      (C) This mode is defined formally in U.S. Department of Defense
      policy regarding system accreditation, but the term is also used
      outside the Defense Department and outside the Government.

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

      (C) Sometimes, the default user name and password are the same in
      each copy of the system. In any case, when the system is put into
      service, the default password should immediately be changed or the
      default account should be disabled.

   $ degauss
      (N) Apply a magnetic field to permanently remove, erase, or clear
      data from a magnetic storage medium, such as a tape or disk
      [NCS25]. Reduce magnetic flux density to zero by applying a
      reversing magnetic field.

   $ degausser
      (N) An electrical device that can degauss magnetic storage media.

   $ DEK
      See: data encryption key.

   $ delta CRL
      (I) A partial CRL that only contains entries for X.509
      certificates that have been revoked since the issuance of a prior,
      base CRL. This method can be used to partition CRLs that become
      too large and unwieldy.

   $ denial of service
      (I) The prevention of authorized access to a system resource or
      the delaying of system operations and functions. (See:
      availability, critical (resource of a system), flooding.)

   $ DES
      See: Data Encryption Standard.

   $ dictionary attack
      (I) An attack that uses a brute-force technique of successively
      trying all the words in some large, exhaustive list.

      (C) For example, an attack on an authentication service by trying
      all possible passwords; or an attack on encryption 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
      (N) A key agreement algorithm published in 1976 by Whitfield
      Diffie and Martin Hellman [DH76, R2631].

      (C) Diffie-Hellman 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.

      (C) The difficulty of breaking Diffie-Hellman is considered to be
      equal to the difficulty of computing discrete logarithms modulo a
      large prime. 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.
      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, capability, public-key certificate.)

      (D) ISDs SHOULD NOT use this term to refer to a signed CRL or CKL.
      Although the recommended definition can be interpreted to include
      those items, the security community does not use the term with
      those meanings.

   $ digital certification
      (D) ISDs SHOULD NOT use this term as a synonym for
      "certification", 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 digital envelope for a recipient is a combination of (a)
      encrypted content data (of any kind) and (b) the content
      encryption key in an encrypted form that has been prepared for the
      use of the recipient.

      (C) In ISDs, this 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 yet widely established.

      (C) 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 PCKS #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
      conveying the content encryption key.

   $ Digital ID(service mark)
      (D) ISDs SHOULD NOT use this term as a synonym for "digital
      certificate" because (a) it is the service mark of a commercial
      firm, (b) it unnecessarily duplicates the meaning of other, well-
      established terms, and (c) a certificate is not always used as
      authentication information. In some contexts, however, it may be
      useful to explain that the key conveyed in a public-key
      certificate can be used to verify an identity and, therefore, that
      the certificate can be thought of as digital identification
      information. (See: identification information.)

   $ digital key
      (C) 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) Analogous to a notary public. Provides a trusted date-and-time
      stamp for a document, so that someone can later prove that the
      document existed at a point in time. May also verify the
      signature(s) on a signed document before applying the stamp. (See:
      notarization.)

   $ digital signature
      (I) A value computed with a cryptographic algorithm and appended
      to 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,
      digitized signature, electronic signature, signer.)

      (I) "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 Part 2]

      (C) Typically, 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.

      (C) Some digital signature schemes use a asymmetric encryption
      algorithm (e.g., see: 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.

      (C) Other digital signature schemes (e.g., see: DSS) transform the
      hash result with an algorithm (e.g., see: 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.

   $ Digital Signature Algorithm (DSA)
      (N) An asymmetric cryptographic algorithm that produces 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:
      Digital Signature Standard.)

   $ Digital Signature Standard (DSS)
      (N) The U.S. Government standard [FP186] that specifies the
      Digital Signature Algorithm (DSA), which involves asymmetric
      cryptography.

   $ 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.

      (C) The set of embedded bits (the digital watermark) 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) ISDs SHOULD NOT use this term because there is no current
      consensus on its definition. Although it appears to be used mainly
      to refer to various forms of digitized images of handwritten
      signatures, the term should be avoided because it might be
      confused with "digital signature".

   $ directory
   $ Directory
      See: directory vs. Directory.

   $ Directory Access Protocol (DAP)
      (N) An OSI protocol [X519] for communication between a Directory
      User Agent (a client) and a Directory System Agent (a server).
      (See: Lightweight Directory Access Protocol.)

   $ directory vs. Directory
      1. (I) Not capitalized: The term "directory" refers generically to
      a database server or other system that provides information--such
      as a digital certificate or CRL--about an entity whose name is
      known.

      2. (I) Capitalized: "Directory" refers specifically to the X.500
      Directory. (See: repository.)

   $ disaster plan
      (D) A synonym for "contingency plan". In the interest of
      consistency, ISDs SHOULD use "contingency plan" instead of
      "disaster plan".

   $ disclosure (i.e., unauthorized disclosure)
      See: (secondary definition under) threat consequence.

   $ discretionary access control (DAC)
      (I) An access control service that enforces a security policy
      based on the identity of system entities and their authorizations
      to access system resources. (See: access control list, identity-
      based security policy, mandatory access control.)

      (C) This service is termed "discretionary" because an entity might
      have access rights that permit the entity, by its own volition, to
      enable another entity to access some resource.

      (O) "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]

   $ disruption
      See: (secondary definition under) threat consequence.

   $ Distinguished Encoding Rules (DER)
      (N) A subset of the Basic Encoding Rules, which gives exactly one
      way to represent any ASN.1 value as an octet string [X690].

      (C) Since there is more than one way to encode ASN.1 in BER, DER
      is used in applications in which a unique encoding is needed, such
      as when a digital signature is computed on an ASN.1 value.

   $ distinguished name (DN)
      (I) An identifier that uniquely represents an object in the X.500
      Directory Information Tree (DIT) [X501]. (See: domain name.)

      (C) 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 Authentication Security Service (DASS)
      (I) An experimental Internet protocol [R1507] that uses
      cryptographic mechanisms to provide strong, mutual authentication
      services in a distributed environment.

   $ 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 might list the certificate.

      (C) 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. 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 (c')
      contain revocation entries for multiple CAs.

   $ DN
      See: distinguished name.

   $ DNS
      See: Domain Name System.

   $ DOI
      See: Domain of Interpretation.

   $ domain
      (I) Security usage: An environment or context that is defined by a
      security policy, security model, or security architecture to
      include a set of system resources and the set of system entities
      that have the right to access the resources. (See: domain of
      interpretation, security perimeter.)

      (I) Internet usage: That part of the Internet domain name space
      tree [R1034] that is at or below the name the 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. (See: Domain Name System.)

      (O) MISSI usage: The domain of a MISSI CA is the set of MISSI
      users whose certificates are signed by the CA.

      (O) OSI usage: An administrative partition of a complex
      distributed OSI system.

   $ domain name
      (I) The style of identifier--a sequence of case-insensitive ASCII
      labels separated by dots ("bbn.com.")--defined for subtrees in the
      Internet Domain Name System [R1034] and used in other 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: distinguished name,
      domain.)

      (C) The domain 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). The root's label is the null

      string, so a complete domain name properly ends in a dot. The top-
      level domains, those immediately below the root, include COM, EDU,
      GOV, INT, MIL, NET, ORG, and two-letter country codes (such as US)
      from ISO-3166. [R1591] (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 translating a domain name-style host name into an
      IP address (e.g., "rosslyn.bbn.com" is "192.1.7.10") and locating
      a host that accepts mail for some mailbox address. [R1034]

      (C) 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.

      (C) Extensions to the DNS [R2065, R2137, R2536] 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 usage: An ISAKMP/IKE DOI defines payload formats,
      exchange types, and conventions for naming security-relevant
      information such as security policies or cryptographic algorithms
      and modes.

      (C) For example, see [R2407]. 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 the nonhierarchical categories of A include
      all of those of B.

   $ dongle
      (I) A portable, physical, electronic device that is required to be
      attached to a computer to enable a particular software program to
      run. (See: token.)

      (C) A dongle is essentially a physical key used for copy
      protection of software, because 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) Reduce the classification level of information in an
      authorized manner.

   $ draft RFC
      (D) ISDs SHOULD NOT use this term, because the Request for Comment
      series is archival in nature and does not have a "draft" category.
      (Instead, see: Internet Draft, Draft Standard (in Internet
      Standard).)

   $ DSA
      See: Digital Signature Algorithm.

   $ DSS
      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
      (D) ISDs SHOULD NOT use this term except when stated as
      "SET(trademark) dual signature" with the following meaning:

      (O) SET usage: A single digital signature that protects two
      separate messages by including the hash results for both sets in a
      single encrypted value. [SET2]

      (C) 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.

   $ EAP
      See: Extensible Authentication Protocol

   $ eavesdropping
      (I) Passive wiretapping done secretly, i.e., without the knowledge
      of the originator or the intended recipients of the communication.

   $ ECB
      See: electronic codebook.

   $ ECDSA
      See: Elliptic Curve Digital Signature Algorithm.

   $ economy of mechanism
      (I) The principle that each security mechanism should be designed
      to be as simple as possible, so that the mechanism can be
      correctly implemented and so that it can be verified that the
      operation of the mechanism enforces the containing system's
      security policy. (See: least privilege.)

   $ EDI
      See: electronic data interchange.

   $ EDIFACT
      See: (secondary definition under) electronic data interchange.

   $ EE
      (D) ISDs SHOULD NOT use this abbreviation because of possible
      confusion among "end entity", "end-to-end encryption", "escrowed
      encryption standard", and other terms.

   $ EES
      See: Escrowed Encryption Standard.

   $ 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, Schn]

   $ electronic codebook (ECB)
      (I) An 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 ciphertext [FP081].

   $ electronic commerce
      (I) General usage: 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.

      (O) SET usage: "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.

      (C) 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 signature
      (D) ISDs SHOULD NOT use this term because there is no current
      consensus on its definition. (Instead, see: digital signature.)

   $ elliptic curve cryptography (ECC)
      (I) A type of asymmetric cryptography based on mathematics of
      groups that are defined by the points on a curve.

      (C) The most efficient implementation of ECC is claimed to be
      stronger per bit of key (against cryptanalysis that uses a brute
      force attack) than any other known form of asymmetric
      cryptography. ECC is based on mathematics different than the kinds
      originally used to define the Diffie-Hellman algorithm and the
      Digital Signature Algorithm. ECC is based on the mathematics of
      groups defined by the points on a curve, where the curve is
      defined by a quadratic equation in a finite field. ECC can be used
      to define both an algorithm for key agreement that is an analog of
      Diffie-Hellman and an algorithm for digital signature that is an
      analog of DSA. (See: ECDSA.)

   $ Elliptic Curve Digital Signature Algorithm (ECDSA)
      (N) A standard [A9062] that is the elliptic curve cryptography
      analog of the Digital Signature Algorithm.

   $ emanation
      (I) An signal (electromagnetic, acoustic, or other medium) that is
      emitted by a system (through radiation or conductance) as a
      consequence (i.e., byproduct) of its operation, and that may
      contain information. (See: TEMPEST.)

   $ emanations security (EMSEC)
      (I) Physical constraints to prevent information compromise through
      signals emanated by a system, particular the application of
      TEMPEST technology to block electromagnetic radiation.

   $ emergency plan
      (D) A synonym for "contingency plan". In the interest of
      consistency, ISDs SHOULD use "contingency plan" instead of
      "emergency plan".

   $ EMSEC
      See: emanations security.

   $ EMV
      (I) An 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 IPsec protocol [R2406] designed to provide a mix
      of security services--especially data confidentiality service--in
      the Internet Protocol. (See: Authentication Header.)

      (C) ESP may be used alone, or in combination with the IPsec AH
      protocol, 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) ISDs SHOULD NOT use this term as a synonym for "encrypt".
      However, see the usage note under "encryption".

   $ encipherment
      (D) ISDs SHOULD NOT use this term as a synonym for "encryption",
      except in special circumstances that are explained in the usage
      discussion under "encryption".

   $ encode
      (I) Use a system of symbols to represent information, which might
      originally have some other representation. (See: decode.)

      (C) Examples include Morse code, ASCII, and BER.

      (D) ISDs SHOULD NOT use this term as a synonym for "encrypt",
      because encoding is not usually intended to conceal meaning.

   $ encrypt
      (I) Cryptographically transform data to produce ciphertext. (See:
      encryption.)

   $ encryption
      (I) Cryptographic transformation of data (called "plaintext") into
      a form (called "ciphertext") that conceals the data's original
      meaning to prevent it from being known or used. If the
      transformation is reversible, the corresponding reversal process
      is called "decryption", which is a transformation that restores
      encrypted data to its original state. (See: cryptography.)

      (C) Usage note: For this concept, ISDs should use the verb "to
      encrypt" (and related variations: encryption, decrypt, and
      decryption). However, because of cultural biases, some
      international usage, particularly ISO and CCITT standards, avoids
      "to encrypt" and instead uses the verb "to encipher" (and related
      variations: encipherment, decipher, decipherment).

      (O) "The cryptographic transformation of data (see: cryptography)
      to produce ciphertext." [I7498 Part 2]

      (C) Usually, the plaintext input to an encryption operation is
      cleartext. But in some cases, the plaintext may be ciphertext that
      was output from another encryption operation. (See:
      superencryption.)

      (C) Encryption and decryption involve a mathematical algorithm for
      transforming data. In addition to the data to be transformed, the
      algorithm has one or more inputs that are control parameters: (a)
      a key value that varies the transformation and, in some cases, (b)
      an initialization value 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.

      C) A v3 X.509 public-key certificate may have a "keyUsage"
      extension that indicates the purpose for which the certified
      public key is intended.

   $ end entity
      (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 a purpose or purposes other than
      signing a digital certificate; i.e., an entity that is not a CA.

      (D) "A certificate subject which uses its public [sic] key for
      purposes other than signing certificates." [X509]

      (C) ISDs SHOULD NOT use the X.509 definition, because it is
      misleading and incomplete. First, the X.509 definition should say
      "private key" rather than "public key" because certificates are
      not usefully signed with a public key. Second, the X.509
      definition is weak 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".

      (C) 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.

      (C) Whether a subject can play both CA and non-CA roles, with
      either the same or different certificates, is a matter of policy.
      (See: certification practice statement.) 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".

   $ end system
      (I) An OSI term for a computer that implements all seven layers of
      the OSIRM and may attach to a subnetwork. (In the context of the
      Internet Protocol Suite, usually called a "host".)

   $ end-to-end encryption
      (I) Continuous protection of data that flows between two points in
      a network, provided by encrypting data when it leaves its source,
      leaving it encrypted while it passes through any intermediate
      computers (such as routers), and decrypting only when the data
      arrives at the intended destination. (See: link encryption,
      wiretapping.)

      (C) 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
      (I) General usage: A system entity, usually a human individual,
      that makes use of system resources, primarily for application
      purposes as opposed to system management purposes.

      (I) PKI usage: A synonym for "end entity"; but the term "end
      entity" is preferred.

   $ 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.)

   $ ephemeral key
      (I) A public key or a private key that is relatively short-lived.
      (See: session key.)

   $ 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 use of a
      symmetric encryption algorithm (SKIPJACK) and a Law Enforcement

      Access Field (LEAF) creation method to implement part of a key
      escrow system that provides for decryption of encrypted
      telecommunications when interception is lawfully authorized.

      (C) Both SKIPJACK and the LEAF are to be implemented in equipment
      used to encrypt and decrypt unclassified, sensitive
      telecommunications data.

   $ ESP
      See: Encapsulating Security Payload.

   $ Estelle
      (N) A language (ISO 9074-1989) for formal specification of
      computer network protocols.

   $ evaluated products list
      (O) General usage: A list of information system equipment items
      that have been evaluated against, and found to be compliant with,
      a particular set of criteria.

      (O) U.S. Department of Defense usage: The Evaluated Products List
      (http://www.radium.ncsc.mil/tpep/epl/) contains items that have
      been evaluated against the TCSEC by the NCSC, or against the
      Common Criteria by the NCSC or one of its partner agencies in
      another county. The List forms Chapter 4 of NSA's "Information
      Systems Security Products and Services Catalogue".

   $ evaluated system
      (I) Refers to a system that has been evaluated against security
      criteria such as the TCSEC or the Common Criteria.

   $ expire
      See: certificate expiration.

   $ exposure
      See: (secondary definition under) threat consequence.

   $ Extensible Authentication Protocol
      (I) A framework that supports multiple, optional authentication
      mechanisms for PPP, including cleartext passwords, challenge-
      response, and arbitrary dialog sequences. [R2284]

      (C) This protocol is intended for use primarily by a host or
      router that connects to a PPP network server via switched circuits
      or dial-up lines.

   $ extension
      (I) A data item defined for optional inclusion in a v3 X.509
      public-key certificate or a v2 X.509 CRL.

      (C) The formats defined in X.509 can be extended to provide
      methods for associating additional attributes with subjects and
      public keys and for managing a certification hierarchy:

       - "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.

       - "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.

       - "Private extension": Additional extensions, each named by an
         OID, can be locally defined as needed by applications or
         communities. (See: PKIX private extension, SET private
         extensions.)

   $ extranet
      (I) A computer network that an organization uses to carry
      application data traffic between the organization and its business
      partners. (See: intranet.)

      (C) An extranet can be implemented securely, either on the
      Internet or using Internet technology, by constructing the
      extranet as a VPN.

   $ fail safe
      (I) A mode of system termination that automatically leaves system
      processes and components in a secure state when a failure occurs
      or is detected in the system.

   $ fail soft
      (I) Selective termination of affected non-essential system
      functions and processes when a failure occurs or is detected in
      the system.

   $ failure control
      (I) A methodology used to provide fail-safe or fail-soft
      termination and recovery of functions and processes when failures
      are detected or occur in a system. [FP039]

   $ Federal Information Processing Standards (FIPS)
      (N) The Federal Information Processing Standards Publication (FIPS
      PUB) series issued by the U.S. National Institute of Standards and
      Technology as technical guidelines for U.S. Government
      procurements of information processing system equipment and
      services. [FP031, FP039, FP046, FP081, FP102, FP113, FP140, FP151,
      FP180, FP185, FP186, FP188]

      (C) Issued 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.

   $ Federal Public-key Infrastructure (FPKI)
      (N) A PKI being planned to establish facilities, specifications,
      and policies needed by the U.S. Federal Government to use public-
      key certificates for INFOSEC, COMSEC, and electronic commerce
      involving unclassified but sensitive applications and interactions
      between Federal agencies as well as with entities of other
      branches of the Federal Government, state, and local governments,
      business, 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 OSI layer 2. Was renamed "FIPS
      PUB 140" when responsibility for protecting unclassified,
      sensitive information was transferred from NSA to NIST, and then
      was superseded by FIPS PUB 140-1.

   $ File Transfer Protocol (FTP)
      (I) A TCP-based, application-layer, Internet Standard protocol
      [R0959] for moving data files from one computer to another.

   $ filtering router
      (I) An internetwork router that selectively prevents the passage
      of data packets according to a security policy.

      (C) A filtering router may be used as a firewall or part of a
      firewall. A router usually receives a packet from a network and
      decides where to forward it on a second network. A filtering
      router does the same, but first decides whether the packet should
      be forwarded at all, according to some security policy. 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]

   $ 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
      (I) A pattern of curves formed by the ridges on a fingertip. (See:
      biometric authentication, thumbprint.)

      (D) ISDs SHOULD NOT use this term as a synonym for "hash result"
      because it mixes concepts in a potentially misleading way.

      (D) ISDs SHOULD NOT use this term with the following PGP
      definition, because the term and definition mix concepts in a
      potentially misleading way and duplicate the meaning of "hash
      result":

      (O) PGP usage: A hash result used to authenticate a public key
      (key fingerprint) or other data. [PGP]

   $ FIPS
      See: Federal Information Processing Standards.

   $ FIPS PUB 140-1
      (N) The U.S. Government standard [FP140] for security requirements
      to be met by a cryptographic module used to protect unclassified
      information in computer and communication systems. (See: Common
      Criteria, FIPS, Federal Standard 1027.)

      (C) 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.

   $ firewall
      (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.)

      (C) 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 security
      policy rules to control traffic that flows in and out of the
      protected network.

      (C) 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 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 intruders out, but usually also
      needs to let authorized users 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
      See: Forum of Incident Response and Security Teams.

   $ 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]

   $ flooding
      (I) An attack that attempts to cause a failure in (especially, in
      the security of) a computer system or other data processing entity
      by providing more input than the entity can process properly.
      (See: denial of service.)

   $ 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.

   $ flow control
      (I) 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. (See: covert channel, simple security property, confinement
      property.)

   $ formal specification
      (I) A specification of hardware or software functionality in a
      computer-readable language; usually a precise mathematical
      description of the behavior of the system with the aim of
      providing a correctness proof.

   $ 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)
      (N) 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 that
      contains a CAPSTONE chip, serial port modems, server boards, smart
      cards, and software implementations.

   $ Forum of Incident Response and Security Teams (FIRST)
      (N) An international consortium of CSIRTs that work together to
      handle computer security incidents and promote preventive
      activities. (See: CSIRT, security incident.)

      (C) FIRST was founded in 1990 and, as of September 1999, had
      nearly 70 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
         government, private industry, academia, and the individual.
       - Enhance the image and status of the CSIRT community.

   $ forward secrecy
      See: public-key forward secrecy.

   $ FPKI
      See: Federal Public-Key Infrastructure.

   $ FTP
      See: File Transfer Protocol.

   $ gateway
      (I) A relay mechanism that attaches to two (or more) computer
      networks that have similar functions but dissimilar
      implementations and that enables host computers on one network to
      communicate with hosts on the other; an intermediate system that
      is the interface between two computer networks. (See: bridge,
      firewall, guard, internetwork, proxy server, router, and
      subnetwork.)

      (C) In theory, gateways are conceivable at any OSI layer. In
      practice, they operate at OSI layer 3 (see: bridge, router) or
      layer 7 (see: proxy server). When the two networks differ in the
      protocol by which they offer service to hosts, the gateway may
      translate one protocol into another or otherwise facilitate
      interoperation of hosts (see: Internet Protocol).

   $ GCA
      See: geopolitical certificate authority.

   $ GeneralizedTime
      (N) The ASN.1 data type "GeneralizedTime" (specified in 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 allowing Coordinated
      Universal Time to be calculated. (See: Coordinated Universal Time,
      UTCTime.)

   $ Generic Security Service Application Program Interface (GSS-API)
      (I) An Internet Standard protocol [R2078] 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 allowing the
      application source code to be ported to different environments.

      (C) "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]." [R2078]

   $ geopolitical certificate authority (GCA)
      (O) SET usage: 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.

   $ Green Book
      (D) Except as an explanatory appositive, ISDs SHOULD NOT use this
      term as a synonym for "Defense Password Management Guideline"
      [CSC2]. Instead, use the full proper name of the document or, in
      subsequent references, a conventional abbreviation. (See: Rainbow
      Series.)

      (D) Usage note: To improve international comprehensibility of
      Internet Standards and the Internet Standards Process, ISDs SHOULD
      NOT use "cute" synonyms for document titles. No matter how popular
      and clearly understood a nickname may be in one community, it is
      likely to cause confusion 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 (at that time, 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.

   $ GRIP
      (I) A contraction of "Guidelines and Recommendations for Security
      Incident Processing", the name of the IETF working group that
      seeks to facilitate consistent handling of security incidents in
      the Internet community. (See: security incident.)

      (C) Guidelines to be produced by the WG will address technology
      vendors, network service providers, and response teams in their
      roles assisting organizations in resolving security incidents.
      These relationships are functional and can exist within and across
      organizational boundaries.

   $ GSS-API
      See: Generic Security Service Application Program Interface.

   $ guard
      (I) A gateway that is interposed between two networks (or
      computers, or other information systems) operating at different
      security levels (one level is usually higher than the other) and
      is trusted to mediate all information transfers between the two
      levels, either to ensure that no sensitive information from the
      first (higher) level is disclosed to the second (lower) level, or
      to protect the integrity of data on the first (higher) level.
      (See: firewall.)

   $ guest login
      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.

   $ hacker
      (I) Someone with a strong interest in computers, who enjoys
      learning about them and experimenting with them. (See: cracker.)

      (C) The recommended definition is the original meaning of the term
      (circa 1960), which then had a neutral or positive connotation of
      "someone who figures things out and makes something cool
      happen". Today, the term is frequently misused, especially by
      journalists, to have the pejorative meaning of cracker.

   $ handle
      (I) (1.) 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. (2.) Noun: An on-
      line pseudonym, particularly one used by a cracker; derived from
      citizens band radio culture.

   $ hardware
      (I) The material physical components of a computer system. (See:
      firmware, software.)

   $ hardware token
      See: token.

   $ hash code
      (D) ISDs SHOULD NOT use this term (especially not as a synonym for
      "hash result") because it mixes concepts in a potentially
      misleading way. A hash result is not a "code" in any sense defined
      by this glossary. (See: code, hash result, hash value, message
      digest.)

   $ hash function
      (I) An algorithm that computes a value based on a data object
      (such as a message or file; usually variable-length; possibly very
      large), thereby mapping the data object to a smaller data object
      (the "hash result") which is usually a fixed-size value. (See:
      checksum, keyed hash.)

      (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]

      (C) The kind of hash function needed for security applications is
      called a "cryptographic hash function", an algorithm for which it
      is computationally infeasible (because no attack is significantly
      more efficient than brute force) to find either (a) a data object
      that maps to a pre-specified hash result (the "one-way" property)
      or (b) two data objects that map to the same hash result (the
      "collision-free" property). (See: MD2, MD4, MD5, SHA-1.)

      (C) A cryptographic hash is "good" in the sense stated in the "O"
      definition for hash function. Any change to an input data object
      will, with high probability, result in a different hash result, so
      that the result of a cryptographic hash makes a good checksum for
      a data object.

   $ hash result
      (I) The output of a hash function. (See: hash code, hash value.)

      (O) "The output produced by a hash function upon processing a
      message" (where "message" is broadly defined as "a digital
      representation of data"). [ABA] (The recommended definition is
      compatible with this ABA definition, but we avoid the unusual
      definition of "message".)

   $ hash value
      (D) ISDs SHOULD NOT use this term (especially not as a synonym for
      "hash result", the output of a hash function) because it might be
      confused with "hashed value" (the input to a hash function). (See:
      hash code, hash result, message digest.)

   $ hierarchical PKI
      (I) A PKI architecture based on a certification hierarchy. (See:
      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.

   $ hierarchy of trust
      (D) ISDs SHOULD NOT use this term with regard to PKI, especially
      not as a synonym for "certification hierarchy", because this term
      mixes concepts in a potentially misleading way. (See:
      certification hierarchy, trust, web of trust.)

   $ 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.)

   $ 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].)

      (C) 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, OPAD = the byte 0x5C repeated B times. HMAC
      is computed by H(K XOR OPAD, H(K XOR IPAD, inputdata)).

      (C) The goals of HMAC are as follows:

       - 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
      (I) A system (e.g., a web server) or a 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.)

      (D) It is likely that other cultures have different metaphors for
      this concept. To ensure international understanding, ISDs should
      not use this term unless they also provide an explanation like
      this one. (See: (usage note under) Green Book.)

   $ host
      (I) General computer network usage: 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.)

      (I) Specific Internet Protocol Suite usage: A networked computer
      that does not forward Internet Protocol packets that are not
      addressed to the computer itself. (See: router.)

      (C) Derivation: As viewed by its users, a host "entertains"
      guests, 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
      See: Hypertext Markup Language.

   $ HTTP
      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. (See: S-HTTP.)

   $ hybrid encryption
      (I) An application of cryptography that combines two or more
      encryption algorithms, particularly a combination of symmetric and
      asymmetric encryption. (E.g., see: digital envelope.)

      (C) Asymmetric algorithms require more computation than
      equivalently strong symmetric ones. Thus, asymmetric encryption is
      not normally used for data confidentiality except in distributing

      symmetric keys in applications where the key data is usually short
      (in terms of bits) compared to the data it protects. (E.g., see:
      MSP, PEM, PGP.)

   $ hyperlink
      (I) In hypertext or hypermedia, an information object (such as a
      word, a phrase, or an image; usually highlighted by color or
      underscoring) that points (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 Hypertext Markup
      Language and accessed using a web browser. (See: hypermedia.)

   $ Hypertext Markup Language (HTML)
      (I) A platform-independent system of syntax and semantics 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. [R1866]

   $ Hypertext Transfer Protocol (HTTP)
      (I) A TCP-based, application-layer, client-server, Internet
      protocol [R2616] used to carry data requests and responses in the
      World Wide Web. (See: hypertext.)

   $ IAB
      See: Internet Architecture Board.

   $ IANA
      See: Internet Assigned Numbers Authority.

   $ ICANN
      See: Internet Corporation for Assigned Names and Numbers.

   $ ICMP
      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
      See: indirect certificate revocation list.

   $ IDEA
      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 Protocol
      (I) An client-server Internet protocol [R1413] for learning the
      identity of a user of a particular TCP connection.

      (C) 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 is not intended for authorization or
      access control. At best, it provides additional auditing
      information with respect to TCP.

   $ 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 Part 2]
      (See: rule-based security policy.)

   $ IEEE
      See: Institute of Electrical and Electronics Engineers, Inc.

   $ IEEE 802.10
      (N) An IEEE committee developing security standards for local area
      networks. (See: SILS.)

   $ IEEE P1363
      (N) An IEEE working group, Standard for Public-Key Cryptography,
      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
      See: Internet Engineering Steering Group.

   $ IETF
      See: Internet Engineering Task Force.

   $ IKE
      See: IPsec Key Exchange.

   $ IMAP4
      See: Internet Message Access Protocol, version 4.

   $ IMAP4 AUTHENTICATE
      (I) A IMAP4 "command" (better described as a transaction type, or
      a protocol-within-a-protocol) 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.)

      (C) 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, GSSAPI, and S/Key--are described
      in [R1731].

   $ in the clear
      (I) Not encrypted. (See: cleartext.)

   $ indirect certificate revocation list (ICRL)
      (I) In X.509, a CRL that may contain certificate revocation
      notifications for certificates issued by CAs other than the issuer
      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.

      (C) Under certain conditions, this notion is equivalent to
      "semantic security".

   $ information
      (I) Facts and ideas, which can be represented (encoded) as various
      forms of data.

   $ Information Technology Security Evaluation Criteria (ITSEC)
      (N) Standard developed for use in the European Union; accommodates
      a wider range of security assurance and functionality combinations
      than the TCSEC. Superseded by the Common Criteria. [ITSEC]

   $ INFOSEC
      (I) Abbreviation for "information security", referring to security
      measures that implement and assure security services in computer
      systems (i.e., COMPUSEC) and communication systems (i.e., COMSEC).

   $ initialization value (IV)
      (I) An input parameter that sets the starting state of a
      cryptographic algorithm or mode. (Sometimes called "initialization
      vector" or "message indicator".)

      (C) An IV can be used to introduce cryptographic variance in
      addition to that provided by a key (see: salt), and to synchronize
      one cryptographic process with another. For an example of the
      latter, cipher block chaining mode requires an IV. [R2405]

   $ initialization vector
      (D) For consistency, ISDs SHOULD NOT use this term as a synonym
      for "initialization value".

   $ insider attack
      See: (secondary definition under) attack.

   $ Institute of Electrical and Electronics Engineers, Inc. (IEEE)
      (N) The IEEE is a not-for-profit association of more than 330,000
      individual members in 150 countries. The IEEE produces 30 percent
      of the world's published literature in electrical engineering,
      computers, and control technology; holds annually more than 300
      major conferences; and has more than 800 active standards with 700
      under development. (See: Standards for Interoperable LAN/MAN
      Security.)

   $ integrity
      See: data integrity, correctness integrity, source integrity,
      system integrity.

   $ integrity check
      (D) ISDs SHOULD NOT use this term as a synonym for "cryptographic
      hash" or "protected checksum", because this term unnecessarily
      duplicates the meaning of other, well-established terms.

   $ intelligent threat
      (I) A circumstance in which an adversary has the technical and
      operational capability to detect and exploit a vulnerability and
      also has the demonstrated, presumed, or inferred intent to do so.
      (See: threat.)

   $ 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
      See: (secondary definition under) ISO.

   $ International Traffic in Arms Regulations (ITAR)
      (N) 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: Wassenaar Arrangement.)

   $ internet
   $ Internet
      See: internet vs. Internet.

   $ 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. [R2026]

   $ 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 [R0792] 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, domain name system management, and root
      server system management functions formerly performed under U.S.
      Government contract by IANA and other entities.

      (C) The Internet Protocol Suite, 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 object identifiers, 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.

      (C) 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: the allocation of IP address space, the assignment
      of protocol parameters, the management of the DNS, and the
      management of the DNS root server system.

   $ Internet Draft
      (I) A working document of the IETF, its areas, and its working
      groups. (Other groups may also distribute working documents as
      Internet Drafts.) 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 "work in progress."

   $ 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. [R2026]

   $ 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. [R2026, R2323]

   $ Internet Message Access Protocol, version 4 (IMAP4)
      (I) An Internet protocol [R2060] 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.)

      (C) IMAP4 has mechanisms for optionally authenticating a client to
      a server and providing other security services. (See: IMAP4
      AUTHENTICATE.)

   $ 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 usage under) certification hierarchy.)

   $ Internet Protocol (IP)
      (I) A Internet Standard protocol (version 4 [R0791] and version 6
      [R2460]) 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. (See: IP address, TCP/IP.)

      (C) In the OSIRM, IP would be located at the top of layer 3.

   $ Internet Protocol security (IPsec)
      (I) (1.) The name of the IETF working group that is specifying a
      security architecture [R2401] and protocols to provide security
      services for Internet Protocol traffic. (2.) A collective name for
      that architecture and set of protocols. (Implementation of IPsec
      protocols is optional for IP version 4, but mandatory for IP
      version 6.) (See: Internet Protocol Security Option.)

      (C) Note that the letters "sec" are lower-case.

      (C) The IPsec architecture 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. The set of security services 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.

   $ 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 the purpose of
      carrying security information about the datagram. (See: IPsec.)

      (D) ISDs SHOULD NOT use this term without a modifier to indicate
      which of the three types is meant.

      1. "DoD Basic Security Option" (IP option type 130): Defined for
      use on U.S. Department of Defense common user data networks.
      Identifies the Defense classification level at which the
      datagram is to be protected and the protection authorities
      whose rules apply to the datagram. [R1108]

      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]

      2. "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]

      3. "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".) Was published as Internet-Draft [CIPSO]; not advanced
      to RFC.

   $ Internet Protocol Suite
      See: (secondary definition under) Internet.

   $ 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.

      (C) ISAKMP supports negotiation of security associations for
      protocols at all TCP/IP 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.

   $ 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. [R2026]

   $ 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. [R2026] (See: RFC.)

      (C) 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 Internet
      Protocol Suite. The "Internet Standards Track" has three levels of
      increasing maturity: Proposed Standard, Draft Standard, and
      Standard. (See: (standards levels under) ISO.)

   $ Internet Standards document (ISD)
      (C) In this Glossary, this term refers to an RFC, Internet-Draft,
      or other item that is produced as part of the Internet Standards
      Process [R2026]. However, neither the term nor the abbreviation is
      widely accepted and, therefore, SHOULD NOT be used in an ISD
      unless it is accompanied by an explanation like this. (See:
      Internet Standard.)

   $ internet vs. Internet
      1. (I) Not capitalized: A popular abbreviation for "internetwork".

      2. (I) Capitalized: "The Internet" is the single, interconnected,
      worldwide system of commercial, government, educational, and other
      computer networks that share the set of protocols specified by the
      IAB [R2026] and the name and address spaces managed by the ICANN.

      (C) The protocol set is named the "Internet Protocol Suite". It
      also is popularly known as "TCP/IP", because TCP and IP are two of
      its fundamental components. These protocols enable a user of any
      one of the networks in the Internet to communicate with, or use
      services located on, any of the other networks.

      (C) Although the Internet does have architectural principles
      [R1958], no Internet Standard formally defines a layered reference
      model for the IPS that is similar to the OSIRM. However, Internet
      community documents do refer (inconsistently) to layers:
      application, socket, transport, internetwork, network, data link,

      and physical. In this Glossary, Internet layers are referred to by
      name to avoid confusing them with OSIRM layers, which are referred
      to by number.

   $ internetwork
      (I) A system of interconnected networks; a network of networks.
      Usually shortened to "internet". (See: internet vs. Internet.)

      (C) An internet is usually built using OSI layer 3 gateways to
      connect a set of subnetworks. When the subnetworks differ in the
      OSI layer 3 protocol service they provide, the gateways sometimes
      implement a uniform internetwork protocol (e.g., IP) that operates
      at the top of layer 3 and hides the underlying 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, virtual private network.)

   $ intruder
      (I) An entity that gains or attempts to gain access to a system or
      system resource without having authorization to do so. (See:
      cracker.)

   $ intrusion
      See: security intrusion.

   $ intrusion detection
      (I) A security service that monitors and analyzes system events
      for the purpose of finding, and providing real-time or near real-
      time warning of, attempts to access system resources in an
      unauthorized manner.

   $ 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].

      (C) 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.

   $ IP
      See: Internet Protocol.

   $ IP address
      (I) A computer's internetwork address that is assigned for use by
      the Internet Protocol and other protocols.

      (C) An IP version 4 [R0791] address is written as a series of four
      8-bit numbers separated by periods. For example, the address of
      the host named "rosslyn.bbn.com" is 192.1.7.10.

      (C) An IP version 6 [R2373] address is written as x:x:x:x:x:x:x:x,
      where each "x" is the hexadecimal value of one of the eight 16-bit
      parts of the address. For example, 1080:0:0:0:8:800:200C:417A and
      FEDC:BA98:7654:3210:FEDC:BA98:7654:3210.

   $ IP Security Option
      See: Internet Protocol Security Option.

   $ IPRA
      See: Internet Policy Registration Authority.

   $ IPsec
      See: Internet Protocol security.

   $ IPsec Key Exchange (IKE)
      (I) An Internet, IPsec, key-establishment protocol [R2409] (partly
      based on OAKLEY) that is intended for putting in place
      authenticated keying material for use with ISAKMP and for other
      security associations, such as in AH and ESP.

   $ IPSO
      See: Internet Protocol Security Option.

   $ ISAKMP
      See: Internet Security Association and Key Management Protocol.

   $ ISD
      See: Internet Standards document.

   $ ISO
      (I) International Organization for Standardization, a voluntary,
      non-treaty, non-government organization, established in 1947, with
      voting members that are designated standards bodies of

      participating nations and non-voting observer organizations. (See:
      ANSI, ITU-T.)

      (C) 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.)

      (C) 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). (See: (standards track levels 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.

   $ ISOC
      See: Internet Society.

   $ issue (a digital certificate or CRL)
      (I) Generate and sign a digital certificate (or CRL) and, usually,
      distribute it and make it available to potential certificate users
      (or CRL users). (See: certificate creation.)

      (C) The ABA Guidelines [ABA] explicitly limit this term to
      certificate creation, and exclude the act of publishing. In
      general usage, however, "issuing" a digital certificate (or CRL)
      includes not only certificate creation but also making it
      available to potential users, such as by storing it in a
      repository or other directory or otherwise publishing it.

   $ issuer
      1. (I) "Issuer" of a certificate or CRL: The CA that signs the
      digital certificate or CRL.

      (C) An X.509 certificate always includes the issuer's name. The
      name may include a common name value.

      2. (N) "Issuer" of a payment card: SET usage: "The financial
      institution or its agent that issues the unique primary account
      number to the cardholder for the payment card brand." [SET2]

      (C) 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
      See: International Traffic in Arms Regulations.

   $ ITSEC
      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.)

      (C) 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
      See: initialization value.

   $ KDC
      See: Key Distribution Center.

   $ KEA
      See: Key Exchange Algorithm.

   $ KEK
      See: key-encrypting key.

   $ Kerberos
      (N) 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. [R1510, Stei]

      (C) Kerberos was developed by Project Athena and is named for the
      three-headed dog guarding Hades.

   $ key
      See: cryptographic key.

   $ key agreement (algorithm or protocol)
      (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 computes the same key value. I.e., each can
      independently generate the same key value, but that key cannot be
      computed by other entities. (See: Diffie-Hellman, key
      establishment, Key Exchange Algorithm, key transport.)

      (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]

      (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]

      (C) For 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 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 that no non-legitimate party possesses the shared
      symmetric key." [A9042]

   $ key center
      (I) A centralized key distribution process (used in symmetric
      cryptography), usually a separate computer system, that uses key-
      encrypting keys (master keys) to encrypt and distribute session
      keys needed in a community of users.

      (C) An ANSI standard [A9017] defines two types of key center: key
      distribution center and key translation center.

   $ key confirmation
      (N) "The assurance of the legitimate participants in a key
      establishment protocol that the intended parties sharing 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 management.)

   $ key distribution center (KDC)
      (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. (See: key translation center.)

      (C) 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 sends that
      encrypted set to Alice for her to forward to Bob, or sends it
      directly to Bob (although the latter option is not supported in
      the ANSI standard [A9017]).

   $ key encapsulation
      See: (secondary definition under) key recovery.

   $ key-encrypting key (KEK)
      (I) A cryptographic key that is used to encrypt other keys, either
      DEKs or other KEKs, but usually is not used to encrypt application
      data.

   $ key escrow
      See: (secondary definition under) key recovery.

   $ key establishment (algorithm or protocol)
      (I) A process that combines the key generation and key
      distribution steps needed to set up or install a secure
      communication association. (See: key agreement, key transport.)

      (O) "The procedure to share a symmetric key among different
      parties by either key agreement or key transport." [A9042]

      (C) Key establishment involves either key agreement or key
      transport:

       - Key transport: One entity generates a secret key and securely
         sends it to the other entity. (Or 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.)

       - Key agreement: No secret is sent from one entity to another.
         Instead, both entities, without prior arrangement except a
         public exchange of data, compute the same secret value. I.e.,

         each can independently generate the same value, but that value
         cannot be computed by other entities.

   $ Key Exchange Algorithm (KEA)
      (N) A key agreement algorithm [NIST] that is similar to the
      Diffie-Hellman algorithm, uses 1024-bit asymmetric keys, and was
      developed and formerly classified at the "Secret" level by NSA.
      (See: CAPSTONE, CLIPPER, FORTEZZA, SKIPJACK.)

      (C) 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 pseudo-random sequence of
      cryptographic key values.

      2. (I) An encryption device that incorporates a key generation
      mechanism and applies the key to plaintext (e.g., by exclusive OR-
      ing the key bit string with the plaintext bit string) to produce
      ciphertext.

   $ key length
      (I) The number of symbols (usually bits) needed to be able to
      represent any of the possible values of a cryptographic key. (See:
      key space.)

   $ key lifetime
      (N) MISSI usage: 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 management
      (I) The process of handling and controlling cryptographic keys and
      related material (such as initialization values) during their life
      cycle in a cryptographic system, including ordering, generating,
      distributing, storing, loading, escrowing, archiving, auditing,
      and destroying the material. (See: key distribution, key escrow,
      keying material, public-key infrastructure.)

      (O) "The generation, storage, distribution, deletion, archiving
      and application of keys in accordance with a security policy."
      [I7498 Part 2]

      (O) "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]

   $ 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.)

   $ key material identifier (KMID)
      (N) MISSI usage: 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.

   $ 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 (e.g.,
      see: Diffie-Hellman, Rivest-Shamir-Adleman).

      (C) A key pair's owner discloses the public key to other system
      entities so they can use the key to encrypt data, verify a digital
      signature, compute a protected checksum, or generate a key in a
      key agreement algorithm. The matching private key is kept secret
      by the owner, who uses it to decrypt data, generate a digital
      signature, verify a protected checksum, or generate a key in a key
      agreement algorithm.

   $ key recovery
      1. (I) A process for learning the value of a cryptographic key
      that was previously used to perform some cryptographic operation.
      (See: cryptanalysis.)

      2. (I) Techniques that provide an intentional, alternate (i.e.,
      secondary) means to access the key used for data confidentiality
      service in an encrypted association. [DOD4]

      (C) We assume that the encryption mechanism has 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 escrow and key encapsulation:

       - "Key escrow": 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.

         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 encapsulation": A key recovery technique for storing
         knowledge of a cryptographic key by encrypting it with another
         key and ensuring that that only certain third parties called
         "recovery agents" can perform the decryption operation to
         retrieve the stored key.

         Key encapsulation typically allows direct retrieval of the
         secret key used to provide data confidentiality.

   $ 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 (used in a symmetric cryptography) that
      implements a key distribution protocol to convey keys between two
      (or more) parties who wish to communicate securely. (See: key
      distribution center.)

      (C) A key translation center translates 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 sends that encrypted set to Alice
      for her to forward to Bob, or sends it directly to Bob (although
      direct distribution is not supported in the ANSI standard
      [A9017]).

   $ key transport (algorithm or protocol)
      (I) A key establishment method by which a secret key is generated
      by one entity in a communication association and securely sent to
      another entity in the association. (See: key agreement.)

      (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]

      (C) For example, a message originator can generate a random
      session key and then use the Rivest-Shamir-Adleman algorithm to
      encrypt that key with the public key of the intended recipient.

   $ key update
      (I) Derive a new key from an existing key. (See: certificate
      rekey.)

   $ key validation
      (N) "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]

   $ 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.)

      (C) If the input data object is changed, a new 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 least two forms of keyed hash:

       - A function based on a keyed encryption algorithm. (E.g., see:
         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. (E.g., see: HMAC.)

   $ keying material
      (I) Data (such as keys, key pairs, and initialization values)
      needed to establish and maintain a cryptographic security
      association.

   $ KMID
      See: key 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 the
      knowing the cryptographic algorithm).

   $ L2F
      See: Layer 2 Forwarding Protocol.

   $ L2TP
      See: Layer 2 Tunneling Protocol.

   $ label
      See: security label.

   $ 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 model
      (I) A security 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] (See: flow control, security
      level, security model.)

      (C) The model describes the semantic structure formed by a finite
      set of security levels, such as those used in military
      organizations.

      (C) A lattice is 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. For 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 (X1, ..., Xm), and c
      is a (possibly empty) subset of a finite set C of non-hierarchical
      categories (C1, ..., Cn) -- together with the "dominate" relation.
      (See: dominate.)

   $ Law Enforcement Access Field (LEAF)
      (N) A data item that is automatically embedded in