This document is obsolete. Please
refer to RFC 4949.
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
Copyright (C) The Internet Society (2000). All Rights Reserved.
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.
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.
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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.
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.
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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.
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".
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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.
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.
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.
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.
$ 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
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(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.
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$ 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]
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(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
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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.
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$ 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.
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(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:
$ attribute authority (I) A CA that issues attribute certificates.
(O) "An authority, trusted by the verifier to delegate privilege, which issues attribute certificates." [FPDAM]
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$ 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.
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$ 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.
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$ 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:
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- 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.)
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(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.
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$ 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.
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$ 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:
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- "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.)
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$ 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.)
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$ 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.
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$ 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.)
$ 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.)
$ 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.
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$ 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.
$ 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.
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$ 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.
$ 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.
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(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
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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.
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(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]
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(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]
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$ 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".
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- 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.
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(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.
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$ 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.)
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$ 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.
$ 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].)
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(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.
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- 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.
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$ 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.)
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$ 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
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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.
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$ 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.
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$ 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.)
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(C) Configuration control helps protect against unauthorized or malicious alteration of a system and thus provides assurance of system integrity. (See: malicious logic.)
$ 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.
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$ 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.
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(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.)
$ 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.
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$ 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 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.
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(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]
$ 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.
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$ 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.
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$ 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.)
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(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
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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]
$ 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.
$ 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.
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$ 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
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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.
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(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]
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(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.
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(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".
$ 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.)
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(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]
$ 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
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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
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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.
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$ 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]
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(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]
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$ 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.
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$ 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".
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$ 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.
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$ 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".
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$ 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
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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.
$ 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.
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$ 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]
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$ 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]
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$ 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.)
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(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.)
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$ 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.
$ 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
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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.
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$ 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.
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$ 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.)
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$ 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.
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$ 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
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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.
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$ 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.
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$ 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]
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$ 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".
$ 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.)
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$ 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
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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.)
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(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.
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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
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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,
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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
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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
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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]
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(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.
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$ 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.)
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$ 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-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 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.,
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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]
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(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:
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- "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]).
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$ 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.
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$ 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