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.
AbstractThis Glossary (191 pages of definitions and 13 pages of references) provides abbreviations, explanations, and recommendations for use of information system security terminology. The intent is to improve the comprehensibility of writing that deals with Internet security, particularly Internet Standards documents (ISDs). To avoid confusion, ISDs should use the same term or definition whenever the same concept is mentioned. To improve international understanding, ISDs should use terms in their plainest, dictionary sense. ISDs should use terms established in standards documents and other well-founded publications and should avoid substituting private or newly made-up terms. ISDs should avoid terms that are proprietary or otherwise favor a particular vendor, or that create a bias toward a particular security technology or mechanism versus other, competing techniques that already exist or might be developed in the future.
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Explanation of Paragraph Markings . . . . . . . . . . . . . . 4 2.1 Recommended Terms with an Internet Basis ("I") . . . . . . 4 2.2 Recommended Terms with a Non-Internet Basis ("N") . . . . 5 2.3 Other Definitions ("O") . . . . . . . . . . . . . . . . . 5 2.4 Deprecated Terms, Definitions, and Uses ("D") . . . . . . 6 2.5 Commentary and Additional Guidance ("C") . . . . . . . . . 6 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 197 5. Security Considerations . . . . . . . . . . . . . . . . . . . 211 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 211 7. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 211 8. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 212 R2026]-- and of all other Internet material, too. Some non-security terms are included to make the Glossary self-contained, but more complete lists of networking terms are available elsewhere [R1208, R1983]. Some glossaries (e.g., [Raym]) list terms that are not listed here but could be applied to Internet security. However, those terms have not been included in this Glossary because they are not appropriate for ISDs. This Glossary marks terms and definitions as being either endorsed or deprecated for use in ISDs, but this Glossary is not an Internet standard. The key words "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are intended to be interpreted the same way as in an Internet Standard [R2119], but this guidance represents only the recommendations of this author. However, this Glossary includes reasons for the recommendations--particularly for the SHOULD NOTs--so that readers can judge for themselves whether to follow the recommendations.
This Glossary supports the goals of the Internet Standards Process: o Clear, Concise, and Easily Understood Documentation This Glossary seeks to improve comprehensibility of security- related content of ISDs. That requires wording to be clear and understandable, and requires the set of security-related terms and definitions to be consistent and self-supporting. Also, the terminology needs to be uniform across all ISDs; i.e., the same term or definition needs to be used whenever and wherever the same concept is mentioned. Harmonization of existing ISDs need not be done immediately, but it is desirable to correct and standardize the terminology when new versions are issued in the normal course of standards development and evolution. o Technical Excellence Just as Internet Standard (STD) protocols should operate effectively, ISDs should use terminology accurately, precisely, and unambiguously to enable Internet Standards to be implemented correctly. o Prior Implementation and Testing Just as STD protocols require demonstrated experience and stability before adoption, ISDs need to use well-established language. Using terms in their plainest, dictionary sense (when appropriate) helps to ensure international understanding. ISDs need to avoid using private, made-up terms in place of generally- accepted terms from standards and other publications. ISDs need to avoid substituting new definitions that conflict with established ones. ISDs need to avoid using "cute" synonyms (e.g., see: Green Book); no matter how popular a nickname may be in one community, it is likely to cause confusion in another. o Openness, Fairness, and Timeliness ISDs need to avoid terms that are proprietary or otherwise favor a particular vendor, or that create a bias toward a particular security technology or mechanism over other, competing techniques that already exist or might be developed in the future. The set of terminology used across the set of ISDs needs to be flexible and adaptable as the state of Internet security art evolves.
Section 3 marks terms and definitions as follows: o Capitalization: Only terms that are proper nouns are capitalized. o Paragraph Marking: Definitions and explanations are stated in paragraphs that are marked as follows: - "I" identifies a RECOMMENDED Internet definition. - "N" identifies a RECOMMENDED non-Internet definition. - "O" identifies a definition that is not recommended as the first choice for Internet documents but is something that authors of Internet documents need to know. - "D" identifies a term or definition that SHOULD NOT be used in Internet documents. - "C" identifies commentary or additional usage guidance. The rest of Section 2 further explains these five markings.
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.
$ ABA Guidelines (N) "American Bar Association (ABA) Digital Signature Guidelines" [ABA], a framework of legal principles for using digital signatures and digital certificates in electronic commerce. $ Abstract Syntax Notation One (ASN.1) (N) A standard for describing data objects. [X680] (C) OSI standards use ASN.1 to specify data formats for protocols. OSI defines functionality in layers. Information objects at higher layers are abstractly defined to be implemented with objects at lower layers. A higher layer may define transfers of abstract objects between computers, and a lower layer may define transfers concretely as strings of bits. Syntax is needed to define abstract objects, and encoding rules are needed to transform between abstract objects and bit strings. (See: Basic Encoding Rules.) (C) In ASN.1, formal names are written without spaces, and separate words in a name are indicated by capitalizing the first letter of each word except the first word. For example, the name of a CRL is "certificateRevocationList". $ ACC See: access control center. $ access (I) The ability and means to communicate with or otherwise interact with a system in order to use system resources to either handle information or gain knowledge of the information the system contains. (O) "A specific type of interaction between a subject and an object that results in the flow of information from one to the other." [NCS04] (C) In this Glossary, "access" is intended to cover any ability to communicate with a system, including one-way communication in either direction. In actual practice, however, entities outside a security perimeter that can receive output from the system but cannot provide input or otherwise directly interact with the system, might be treated as not having "access" and, therefore, be exempt from security policy requirements, such as the need for a security clearance. $ access control (I) Protection of system resources against unauthorized access; a process by which use of system resources is regulated according to a security policy and is permitted by only authorized entities
(users, programs, processes, or other systems) according to that policy. (See: access, access control service.) (O) "The prevention of unauthorized use of a resource, including the prevention of use of a resource in an unauthorized manner." [I7498 Part 2] $ access control center (ACC) (I) A computer containing a database with entries that define a security policy for an access control service. (C) An ACC is sometimes used in conjunction with a key center to implement access control in a key distribution system for symmetric cryptography. $ access control list (ACL) (I) A mechanism that implements access control for a system resource by enumerating the identities of the system entities that are permitted to access the resource. (See: capability.) $ access control service (I) A security service that protects against a system entity using a system resource in a way not authorized by the system's security policy; in short, protection of system resources against unauthorized access. (See: access control, discretionary access control, identity-based security policy, mandatory access control, rule-based security policy.) (C) This service includes protecting against use of a resource in an unauthorized manner by an entity that is authorized to use the resource in some other manner. The two basic mechanisms for implementing this service are ACLs and tickets. $ access mode (I) A distinct type of data processing operation--e.g., read, write, append, or execute--that a subject can potentially perform on an object in a computer system. $ accountability (I) The property of a system (including all of its system resources) that ensures that the actions of a system entity may be traced uniquely to that entity, which can be held responsible for its actions. (See: audit service.) (C) Accountability permits detection and subsequent investigation of security breaches.
$ accredit $ accreditation (I) An administrative declaration by a designated authority that an information system is approved to operate in a particular security configuration with a prescribed set of safeguards. [FP102] (See: certification.) (C) An accreditation is usually based on a technical certification of the system's security mechanisms. The terms "certification" and "accreditation" are used more in the U.S. Department of Defense and other government agencies than in commercial organizations. However, the concepts apply any place where managers are required to deal with and accept responsibility for security risks. The American Bar Association is developing accreditation criteria for CAs. $ ACL See: access control list. $ acquirer (N) SET usage: "The financial institution that establishes an account with a merchant and processes payment card authorizations and payments." [SET1] (O) "The institution (or its agent) that acquires from the card acceptor the financial data relating to the transaction and initiates that data into an interchange system." [SET2] $ active attack See: (secondary definition under) attack. $ active wiretapping See: (secondary definition under) wiretapping. $ add-on security (I) "The retrofitting of protection mechanisms, implemented by hardware or software, after the [automatic data processing] system has become operational." [FP039] $ administrative security (I) Management procedures and constraints to prevent unauthorized access to a system. (See: security architecture.) (O) "The management constraints, operational procedures, accountability procedures, and supplemental controls established to provide an acceptable level of protection for sensitive data." [FP039]
(C) Examples include clear delineation and separation of duties, and configuration control. $ Advanced Encryption Standard (AES) (N) A future FIPS publication being developed by NIST to succeed DES. Intended to specify an unclassified, publicly-disclosed, symmetric encryption algorithm, available royalty-free worldwide. $ adversary (I) An entity that attacks, or is a threat to, a system. $ aggregation (I) A circumstance in which a collection of information items is required to be classified at a higher security level than any of the individual items that comprise it. $ AH See: Authentication Header $ algorithm (I) A finite set of step-by-step instructions for a problem- solving or computation procedure, especially one that can be implemented by a computer. (See: cryptographic algorithm.) $ alias (I) A name that an entity uses in place of its real name, usually for the purpose of either anonymity or deception. $ American National Standards Institute (ANSI) (N) A private, not-for-profit association of users, manufacturers, and other organizations, that administers U.S. private sector voluntary standards. (C) ANSI is the sole U.S. representative to the two major non- treaty international standards organizations, ISO and, via the U.S. National Committee (USNC), the International Electrotechnical Commission (IEC). $ anonymous (I) The condition of having a name that is unknown or concealed. (See: anonymous login.) (C) An application may require security services that maintain anonymity of users or other system entities, perhaps to preserve their privacy or hide them from attack. To hide an entity's real name, an alias may be used. For example, a financial institution may assign an account number. Parties to a transaction can thus remain relatively anonymous, but can also accept the transaction
as legitimate. Real names of the parties cannot be easily determined by observers of the transaction, but an authorized third party may be able to map an alias to a real name, such as by presenting the institution with a court order. In other applications, anonymous entities may be completely untraceable. $ anonymous login (I) An access control feature (or, rather, an access control weakness) in many Internet hosts that enables users to gain access to general-purpose or public services and resources on a host (such as allowing any user to transfer data using File Transfer Protocol) without having a pre-established, user-specific account (i.e., user name and secret password). (C) This feature exposes a system to more threats than when all the users are known, pre-registered entities that are individually accountable for their actions. A user logs in using a special, publicly known user name (e.g., "anonymous", "guest", or "ftp"). To use the public login name, the user is not required to know a secret password and may not be required to input anything at all except the name. In other cases, to complete the normal sequence of steps in a login protocol, the system may require the user to input a matching, publicly known password (such as "anonymous") or may ask the user for an e-mail address or some other arbitrary character string. $ APOP See: POP3 APOP. $ archive (I) (1.) Noun: A collection of data that is stored for a relatively long period of time for historical and other purposes, such as to support audit service, availability service, or system integrity service. (See: backup.) (2.) Verb: To store data in such a way. (See: back up.) (C) A digital signature may need to be verified many years after the signing occurs. The CA--the one that issued the certificate containing the public key needed to verify that signature--may not stay in operation that long. So every CA needs to provide for long-term storage of the information needed to verify the signatures of those to whom it issues certificates. $ ARPANET (N) Advanced Research Projects Agency Network, a pioneer packet- switched network that was built in the early 1970s under contract to the U.S. Government, led to the development of today's Internet, and was decommissioned in June 1990.
$ ASN.1 See: Abstract Syntax Notation One. $ association (I) A cooperative relationship between system entities, usually for the purpose of transferring information between them. (See: security association.) $ assurance (I) (1.) An attribute of an information system that provides grounds for having confidence that the system operates such that the system security policy is enforced. (2.) A procedure that ensures a system is developed and operated as intended by the system's security policy. $ assurance level (I) Evaluation usage: A specific level on a hierarchical scale representing successively increased confidence that a target of evaluation adequately fulfills the requirements. (E.g., see: TCSEC.) $ asymmetric cryptography (I) A modern branch of cryptography (popularly known as "public- key cryptography") in which the algorithms employ a pair of keys (a public key and a private key) and use a different component of the pair for different steps of the algorithm. (See: key pair.) (C) Asymmetric algorithms have key management advantages over equivalently strong symmetric ones. First, one key of the pair does not need to be known by anyone but its owner; so it can more easily be kept secret. Second, although the other key of the pair is shared by all entities that use the algorithm, that key does not need to be kept secret from other, non-using entities; so the key distribution part of key management can be done more easily. (C) For encryption: In an asymmetric encryption algorithm (e.g., see: RSA), when Alice wants to ensure confidentiality for data she sends to Bob, she encrypts the data with a public key provided by Bob. Only Bob has the matching private key that is needed to decrypt the data. (C) For signature: In an asymmetric digital signature algorithm (e.g., see: DSA), when Alice wants to ensure data integrity or provide authentication for data she sends to Bob, she uses her private key to sign the data (i.e., create a digital signature based on the data). To verify the signature, Bob uses the matching public key that Alice has provided.
(C) For key agreement: In an asymmetric key agreement algorithm (e.g., see: Diffie-Hellman), Alice and Bob each send their own public key to the other person. Then each uses their own private key and the other's public key to compute the new key value. $ attack (I) An assault on system security that derives from an intelligent threat, i.e., an intelligent act that is a deliberate attempt (especially in the sense of a method or technique) to evade security services and violate the security policy of a system. (See: penetration, violation, vulnerability.) - Active vs. passive: An "active attack" attempts to alter system resources or affect their operation. A "passive attack" attempts to learn or make use of information from the system but does not affect system resources. (E.g., see: wiretapping.) - Insider vs. outsider: An "inside attack" is an attack initiated by an entity inside the security perimeter (an "insider"), i.e., an entity that is authorized to access system resources but uses them in a way not approved by those who granted the authorization. An "outside attack" is initiated from outside the perimeter, by an unauthorized or illegitimate user of the system (an "outsider"). In the Internet, potential outside attackers range from amateur pranksters to organized criminals, international terrorists, and hostile governments. (C) The term "attack" relates to some other basic security terms as shown in the following diagram: + - - - - - - - - - - - - + + - - - - + + - - - - - - - - - - -+ | An Attack: | |Counter- | | A System Resource: | | i.e., A Threat Action | | measure | | Target of the Attack | | +----------+ | | | | +-----------------+ | | | Attacker |<==================||<========= | | | | i.e., | Passive | | | | | Vulnerability | | | | A Threat |<=================>||<========> | | | | Agent | or Active | | | | +-------|||-------+ | | +----------+ Attack | | | | VVV | | | | | | Threat Consequences | + - - - - - - - - - - - - + + - - - - + + - - - - - - - - - - -+ $ attribute authority (I) A CA that issues attribute certificates. (O) "An authority, trusted by the verifier to delegate privilege, which issues attribute certificates." [FPDAM]
$ attribute certificate (I) A digital certificate that binds a set of descriptive data items, other than a public key, either directly to a subject name or to the identifier of another certificate that is a public-key certificate. [X509] (O) "A set of attributes of a user together with some other information, rendered unforgeable by the digital signature created using the private key of the CA which issued it." [X509] (O) "A data structure that includes some attribute values and identification information about the owner of the attribute certificate, all digitally signed by an Attribute Authority. This authority's signature serves as the guarantee of the binding between the attributes and their owner." [FPDAM] (C) A public-key certificate binds a subject name to a public key value, along with information needed to perform certain cryptographic functions. Other attributes of a subject, such as a security clearance, may be certified in a separate kind of digital certificate, called an attribute certificate. A subject may have multiple attribute certificates associated with its name or with each of its public-key certificates. (C) An attribute certificate might be issued to a subject in the following situations: - Different lifetimes: When the lifetime of an attribute binding is shorter than that of the related public-key certificate, or when it is desirable not to need to revoke a subject's public key just to revoke an attribute. - Different authorities: When the authority responsible for the attributes is different than the one that issues the public-key certificate for the subject. (There is no requirement that an attribute certificate be issued by the same CA that issued the associated public-key certificate.) $ audit service (I) A security service that records information needed to establish accountability for system events and for the actions of system entities that cause them. (See: security audit.) $ audit trail See: security audit trail.
$ AUTH See: POP3 AUTH. $ authentic signature (I) A signature (particularly a digital signature) that can be trusted because it can be verified. (See: validate vs. verify.) $ authenticate (I) Verify (i.e., establish the truth of) an identity claimed by or for a system entity. (See: authentication.) (D) In general English usage, this term usually means "to prove genuine" (e.g., an art expert authenticates a Michelangelo painting). But the recommended definition carries a much narrower meaning. For example, to be precise, an ISD SHOULD NOT say "the host authenticates each received datagram". Instead, the ISD SHOULD say "the host authenticates the origin of each received datagram". In most cases, we also can say "and verifies the datagram's integrity", because that is usually implied. (See: ("relationship between data integrity service and authentication services" under) data integrity service.) (D) ISDs SHOULD NOT talk about authenticating a digital signature or digital certificate. Instead, we "sign" and then "verify" digital signatures, and we "issue" and then "validate" digital certificates. (See: validate vs. verify.) $ authentication (I) The process of verifying an identity claimed by or for a system entity. (See: authenticate, authentication exchange, authentication information, credential, data origin authentication, peer entity authentication.) (C) An authentication process consists of two steps: 1. Identification step: Presenting an identifier to the security system. (Identifiers should be assigned carefully, because authenticated identities are the basis for other security services, such as access control service.) 2. Verification step: Presenting or generating authentication information that corroborates the binding between the entity and the identifier. (See: verification.) (C) See: ("relationship between data integrity service and authentication services" under) data integrity service.
$ authentication code (D) ISDs SHOULD NOT use this term as a synonym for any form of checksum, whether cryptographic or not. The word "authentication" is misleading because the mechanism involved usually serves a data integrity function rather than an authentication function, and the word "code" is misleading because it implies that either encoding or encryption is involved or that the term refers to computer software. (See: message authentication code.) $ authentication exchange (I) A mechanism to verify the identity of an entity by means of information exchange. (O) "A mechanism intended to ensure the identity of an entity by means of information exchange." [I7498 Part 2] $ Authentication Header (AH) (I) An Internet IPsec protocol [R2402] designed to provide connectionless data integrity service and data origin authentication service for IP datagrams, and (optionally) to provide protection against replay attacks. (C) Replay protection may be selected by the receiver when a security association is established. AH authenticates upper-layer protocol data units and as much of the IP header as possible. However, some IP header fields may change in transit, and the value of these fields, when the packet arrives at the receiver, may not be predictable by the sender. Thus, the values of such fields cannot be protected end-to-end by AH; protection of the IP header by AH is only partial when such fields are present. (C) AH may be used alone, or in combination with the IPsec ESP protocol, or in a nested fashion with tunneling. Security services can be provided between a pair of communicating hosts, between a pair of communicating security gateways, or between a host and a gateway. ESP can provide the same security services as AH, and ESP can also provide data confidentiality service. The main difference between authentication services provided by ESP and AH is the extent of the coverage; ESP does not protect IP header fields unless they are encapsulated by AH. $ authentication information (I) Information used to verify an identity claimed by or for an entity. (See: authentication, credential.) (C) Authentication information may exist as, or be derived from, one of the following:
- Something the entity knows. (See: password). - Something the entity possesses. (See: token.) - Something the entity is. (See: biometric authentication.) $ authentication service (I) A security service that verifies an identity claimed by or for an entity. (See: authentication.) (C) In a network, there are two general forms of authentication service: data origin authentication service and peer entity authentication service. $ authenticity (I) The property of being genuine and able to be verified and be trusted. (See: authenticate, authentication, validate vs. verify) $ authority (D) "An entity, responsible for the issuance of certificates." [FPDAM] (C) ISDs SHOULD NOT use this term as a synonym for AA, CA, RA, ORA, or similar terms, because it may cause confusion. Instead, use the full term at the first instance of usage and then, if it is necessary to shorten text, use the style of abbreviation defined in this Glossary. (C) ISDs SHOULD NOT use this definition for any PKI entity, because the definition is ambiguous with regard to whether the entity actually issues certificates (e.g., attribute authority or certification authority) or just has accountability for processes that precede or follow signing (e.g., registration authority). (See: issue.) $ authority certificate (D) "A certificate issued to an authority (e.g. either to a certification authority or to an attribute authority)." [FPDAM] (See: authority.) (C) ISDs SHOULD NOT use this term or definition because they are ambiguous with regard to which specific types of PKI entities they address. $ authority revocation list (ARL) (I) A data structure that enumerates digital certificates that were issued to CAs but have been invalidated by their issuer prior to when they were scheduled to expire. (See: certificate expiration, X.509 authority revocation list.)
(O) "A revocation list containing a list of public-key certificates issued to authorities, which are no longer considered valid by the certificate issuer." [FPDAM] $ authorization $ authorize (I) (1.) An "authorization" is a right or a permission that is granted to a system entity to access a system resource. (2.) An "authorization process" is a procedure for granting such rights. (3.) To "authorize" means to grant such a right or permission. (See: privilege.) (O) SET usage: "The process by which a properly appointed person or persons grants permission to perform some action on behalf of an organization. This process assesses transaction risk, confirms that a given transaction does not raise the account holder's debt above the account's credit limit, and reserves the specified amount of credit. (When a merchant obtains authorization, payment for the authorized amount is guaranteed--provided, of course, that the merchant followed the rules associated with the authorization process.)" [SET2] $ automated information system (I) An organized assembly of resources and procedures--i.e., computing and communications equipment and services, with their supporting facilities and personnel--that collect, record, process, store, transport, retrieve, or display information to accomplish a specified set of functions. $ availability (I) The property of a system or a system resource being accessible and usable upon demand by an authorized system entity, according to performance specifications for the system; i.e., a system is available if it provides services according to the system design whenever users request them. (See: critical, denial of service, reliability, survivability.) (O) "The property of being accessible and usable upon demand by an authorized entity." [I7498 Part 2] $ availability service (I) A security service that protects a system to ensure its availability. (C) This service addresses the security concerns raised by denial- of-service attacks. It depends on proper management and control of system resources, and thus depends on access control service and other security services.
$ back door (I) A hardware or software mechanism that (a) provides access to a system and its resources by other than the usual procedure, (b) was deliberately left in place by the system's designers or maintainers, and (c) usually is not publicly known. (See: trap door.) (C) For example, a way to access a computer other than through a normal login. Such access paths do not necessarily have malicious intent; e.g., operating systems sometimes are shipped by the manufacturer with privileged accounts intended for use by field service technicians or the vendor's maintenance programmers. (See: trap door.) $ back up vs. backup (I) Verb "back up": To store data for the purpose of creating a backup copy. (See: archive.) (I) Noun/adjective "backup": (1.) A reserve copy of data that is stored separately from the original, for use if the original becomes lost or damaged. (See: archive.) (2.) Alternate means to permit performance of system functions despite a disaster to system resources. (See: contingency plan.) $ baggage (D) ISDs SHOULD NOT use this term to describe a data element except when stated as "SET(trademark) baggage" with the following meaning: (O) SET usage: An "opaque encrypted tuple, which is included in a SET message but appended as external data to the PKCS encapsulated data. This avoids superencryption of the previously encrypted tuple, but guarantees linkage with the PKCS portion of the message." [SET2] $ bandwidth (I) Commonly used to mean the capacity of a communication channel to pass data through the channel in a given amount of time. Usually expressed in bits per second. $ bank identification number (BIN) (N) The digits of a credit card number that identify the issuing bank. (See: primary account number.) (O) SET usage: The first six digits of a primary account number.
$ Basic Encoding Rules (BER) (I) A standard for representing ASN.1 data types as strings of octets. [X690] (See: Distinguished Encoding Rules.) $ bastion host (I) A strongly protected computer that is in a network protected by a firewall (or is part of a firewall) and is the only host (or one of only a few hosts) in the network that can be directly accessed from networks on the other side of the firewall. (C) Filtering routers in a firewall typically restrict traffic from the outside network to reaching just one host, the bastion host, which usually is part of the firewall. Since only this one host can be directly attacked, only this one host needs to be very strongly protected, so security can be maintained more easily and less expensively. However, to allow legitimate internal and external users to access application resources through the firewall, higher layer protocols and services need to be relayed and forwarded by the bastion host. Some services (e.g., DNS and SMTP) have forwarding built in; other services (e.g., TELNET and FTP) require a proxy server on the bastion host. $ BCA See: brand certification authority. $ BCI See: brand CRL identifier. $ Bell-LaPadula Model (N) A formal, mathematical, state-transition model of security policy for multilevel-secure computer systems. [Bell] (C) The model separates computer system elements into a set of subjects and a set of objects. To determine whether or not a subject is authorized for a particular access mode on an object, the clearance of the subject is compared to the classification of the object. The model defines the notion of a "secure state", in which the only permitted access modes of subjects to objects are in accordance with a specified security policy. It is proven that each state transition preserves security by moving from secure state to secure state, thereby proving that the system is secure. (C) In this model, a multilevel-secure system satisfies several rules, including the following:
- "Confinement property" (also called "*-property", pronounced "star property"): A subject has write access to an object only if classification of the object dominates the clearance of the subject. - "Simple security property": A subject has read access to an object only if the clearance of the subject dominates the classification of the object. - "Tranquillity property": The classification of an object does not change while the object is being processed by the system. $ BER See: Basic Encoding Rules. $ beyond A1 (O) (1.) Formally, a level of security assurance that is beyond the highest level of criteria specified by the TCSEC. (2.) Informally, a level of trust so high that it cannot be provided or verified by currently available assurance methods, and particularly not by currently available formal methods. $ BIN See: bank identification number. $ bind (I) To inseparably associate by applying some mechanism, such as when a CA uses a digital signature to bind together a subject and a public key in a public-key certificate. $ biometric authentication (I) A method of generating authentication information for a person by digitizing measurements of a physical characteristic, such as a fingerprint, a hand shape, a retina pattern, a speech pattern (voiceprint), or handwriting. $ bit (I) The smallest unit of information storage; a contraction of the term "binary digit"; one of two symbols--"0" (zero) and "1" (one) --that are used to represent binary numbers. $ BLACK (I) Designation for information system equipment or facilities that handle (and for data that contains) only ciphertext (or, depending on the context, only unclassified information), and for such data itself. This term derives from U.S. Government COMSEC terminology. (See: RED, RED/BLACK separation.)
$ block cipher (I) An encryption algorithm that breaks plaintext into fixed-size segments and uses the same key to transform each plaintext segment into a fixed-size segment of ciphertext. (See: mode, stream cipher.) (C) For example, Blowfish, DEA, IDEA, RC2, and SKIPJACK. However, a block cipher can be adapted to have a different external interface, such as that of a stream cipher, by using a mode of operation to "package" the basic algorithm. $ Blowfish (N) A symmetric block cipher with variable-length key (32 to 448 bits) designed in 1993 by Bruce Schneier as an unpatented, license-free, royalty-free replacement for DES or IDEA. [Schn] $ brand (I) A distinctive mark or name that identifies a product or business entity. (O) SET usage: The name of a payment card. Financial institutions and other companies have founded payment card brands, protect and advertise the brands, establish and enforce rules for use and acceptance of their payment cards, and provide networks to interconnect the financial institutions. These brands combine the roles of issuer and acquirer in interactions with cardholders and merchants. [SET1] $ brand certification authority (BCA) (O) SET usage: A CA owned by a payment card brand, such as MasterCard, Visa, or American Express. [SET2] (See: certification hierarchy, SET.) $ brand CRL identifier (BCI) (O) SET usage: A digitally signed list, issued by a BCA, of the names of CAs for which CRLs need to be processed when verifying signatures in SET messages. [SET2] $ break (I) Cryptographic usage: To successfully perform cryptanalysis and thus succeed in decrypting data or performing some other cryptographic function, without initially having knowledge of the key that the function requires. (This term applies to encrypted data or, more generally, to a cryptographic algorithm or cryptographic system.)
$ bridge (I) A computer that is a gateway between two networks (usually two LANs) at OSI layer 2. (See: router.) $ British Standard 7799 (N) Part 1 is a standard code of practice and provides guidance on how to secure an information system. Part 2 specifies the management framework, objectives, and control requirements for information security management systems [B7799]. The certification scheme works like ISO 9000. It is in use in the UK, the Netherlands, Australia, and New Zealand and might be proposed as an ISO standard or adapted to be part of the Common Criteria. $ browser (I) An client computer program that can retrieve and display information from servers on the World Wide Web. (C) For example, Netscape's Navigator and Communicator, and Microsoft's Explorer. $ brute force (I) A cryptanalysis technique or other kind of attack method involving an exhaustive procedure that tries all possibilities, one-by-one. (C) For example, for ciphertext where the analyst already knows the decryption algorithm, a brute force technique to finding the original plaintext is to decrypt the message with every possible key. $ BS7799 See: British Standard 7799. $ byte (I) A fundamental unit of computer storage; the smallest addressable unit in a computer's architecture. Usually holds one character of information and, today, usually means eight bits. (See: octet.) (C) Larger than a "bit", but smaller than a "word". Although "byte" almost always means "octet" today, bytes had other sizes (e.g., six bits, nine bits) in earlier computer architectures. $ CA See: certification authority.
$ CA certificate (I) "A [digital] certificate for one CA issued by another CA." [X509] (C) That is, a digital certificate whose holder is able to issue digital certificates. A v3 X.509 public-key certificate may have a "basicConstraints" extension containing a "cA" value that specifically "indicates whether or not the public key may be used to verify certificate signatures." $ call back (I) An authentication technique for terminals that remotely access a computer via telephone lines. The host system disconnects the caller and then calls back on a telephone number that was previously authorized for that terminal. $ capability (I) A token, usually an unforgeable data value (sometimes called a "ticket") that gives the bearer or holder the right to access a system resource. Possession of the token is accepted by a system as proof that the holder has been authorized to access the resource named or indicated by the token. (See: access control list, credential, digital certificate.) (C) This concept can be implemented as a digital certificate. (See: attribute certificate.) $ CAPI See: cryptographic application programming interface. $ CAPSTONE chip (N) An integrated circuit (the Mykotronx, Inc. MYK-82) with a Type II cryptographic processor that implements SKIPJACK, KEA, DSA, SHA, and basic mathematical functions to support asymmetric cryptography, and includes the key escrow feature of the CLIPPER chip. (See: FORTEZZA card.) $ card See: cryptographic card, FORTEZZA card, payment card, PC card, smart card, token. $ card backup See: token backup. $ card copy See: token copy.
$ card restore See: token restore. $ cardholder (I) An entity that has been issued a card. (O) SET usage: "The holder of a valid payment card account and user of software supporting electronic commerce." [SET2] A cardholder is issued a payment card by an issuer. SET ensures that in the cardholder's interactions with merchants, the payment card account information remains confidential. [SET1] $ cardholder certificate (O) SET usage: A digital certificate that is issued to a cardholder upon approval of the cardholder's issuing financial institution and that is transmitted to merchants with purchase requests and encrypted payment instructions, carrying assurance that the account number has been validated by the issuing financial institution and cannot be altered by a third party. [SET1] $ cardholder certification authority (CCA) (O) SET usage: A CA responsible for issuing digital certificates to cardholders and operated on behalf of a payment card brand, an issuer, or another party according to brand rules. A CCA maintains relationships with card issuers to allow for the verification of cardholder accounts. A CCA does not issue a CRL but does distribute CRLs issued by root CAs, brand CAs, geopolitical CAs, and payment gateway CAs. [SET2] $ CAST (N) A design procedure for symmetric encryption algorithms, and a resulting family of algorithms, invented by C.A. (Carlisle Adams) and S.T. (Stafford Tavares). [R2144, R2612] $ category (I) A grouping of sensitive information items to which a non- hierarchical restrictive security label is applied to increase protection of the data. (See: compartment.) $ CAW See: certification authority workstation. $ CBC See: cipher block chaining. $ CCA See: cardholder certification authority.
$ CCITT (N) Acronym for French translation of International Telephone and Telegraph Consultative Committee. Now renamed ITU-T. $ CERT See: computer emergency response team. $ certificate (I) General English usage: A document that attests to the truth of something or the ownership of something. (C) Security usage: See: capability, digital certificate. (C) PKI usage: See: attribute certificate, public-key certificate. $ certificate authority (D) ISDs SHOULD NOT use this term because it looks like sloppy use of "certification authority", which is the term standardized by X.509. $ certificate chain (D) ISDs SHOULD NOT use this term because it duplicates the meaning of a standardized term. Instead, use "certification path". $ certificate chain validation (D) ISDs SHOULD NOT use this term because it duplicates the meaning of standardized terms and mixes concepts in a potentially misleading way. Instead, use "certificate validation" or "path validation", depending on what is meant. (See: validate vs. verify.) $ certificate creation (I) The act or process by which a CA sets the values of a digital certificate's data fields and signs it. (See: issue.) $ certificate expiration (I) The event that occurs when a certificate ceases to be valid because its assigned lifetime has been exceeded. (See: certificate revocation, validity period.) $ certificate extension See: extension.
$ certificate holder (D) ISDs SHOULD NOT use this term as a synonym for the subject of a digital certificate because the term is potentially ambiguous. For example, the term could also refer to a system entity, such as a repository, that simply has possession of a copy of the certificate. (See: certificate owner.) $ certificate management (I) The functions that a CA may perform during the life cycle of a digital certificate, including the following: - Acquire and verify data items to bind into the certificate. - Encode and sign the certificate. - Store the certificate in a directory or repository. - Renew, rekey, and update the certificate. - Revoke the certificate and issue a CRL. (See: archive management, certificate management, key management, security architecture, token management.) $ certificate owner (D) ISDs SHOULD NOT use this term as a synonym for the subject of a digital certificate because the term is potentially ambiguous. For example, the term could also refer to a system entity, such as a corporation, that has acquired a certificate to operate some other entity, such as a Web server. (See: certificate holder.) $ certificate policy (I) "A named set of rules that indicates the applicability of a certificate to a particular community and/or class of application with common security requirements." [X509] (See: certification practice statement.) (C) A certificate policy can help a certificate user decide whether a certificate should be trusted in a particular application. "For example, a particular certificate policy might indicate applicability of a type of certificate for the authentication of electronic data interchange transactions for the trading goods within a given price range." [R2527] (C) A v3 X.509 public-key certificate may have a "certificatePolicies" extension that lists certificate policies, recognized by the issuing CA, that apply to the certificate and govern its use. Each policy is denoted by an object identifier and may optionally have certificate policy qualifiers.
(C) SET usage: Every SET certificate specifies at least one certificate policy, that of the SET root CA. SET uses certificate policy qualifiers to point to the actual policy statement and to add qualifying policies to the root policy. (See: SET qualifier.) $ certificate policy qualifier (I) Information that pertains to a certificate policy and is included in a "certificatePolicies" extension in a v3 X.509 public-key certificate. $ certificate reactivation (I) The act or process by which a digital certificate, which a CA has designated for revocation but not yet listed on a CRL, is returned to the valid state. $ certificate rekey (I) The act or process by which an existing public-key certificate has its public key value changed by issuing a new certificate with a different (usually new) public key. (See: certificate renewal, certificate update, rekey.) (C) For an X.509 public-key certificate, the essence of rekey is that the subject stays the same and a new public key is bound to that subject. Other changes are made, and the old certificate is revoked, only as required by the PKI and CPS in support of the rekey. If changes go beyond that, the process is a "certificate update". (O) MISSI usage: To rekey a MISSI X.509 public-key certificate means that the issuing authority creates a new certificate that is identical to the old one, except the new one has a new, different KEA key; or a new, different DSS key; or new, different KEA and DSS keys. The new certificate also has a different serial number and may have a different validity period. A new key creation date and maximum key lifetime period are assigned to each newly generated key. If a new KEA key is generated, that key is assigned a new KMID. The old certificate remains valid until it expires, but may not be further renewed, rekeyed, or updated. $ certificate renewal (I) The act or process by which the validity of the data binding asserted by an existing public-key certificate is extended in time by issuing a new certificate. (See: certificate rekey, certificate update.) (C) For an X.509 public-key certificate, this term means that the validity period is extended (and, of course, a new serial number is assigned) but the binding of the public key to the subject and
to other data items stays the same. The other data items are changed, and the old certificate is revoked, only as required by the PKI and CPS to support the renewal. If changes go beyond that, the process is a "certificate rekey" or "certificate update". $ certificate request (D) ISDs SHOULD NOT use this term because it looks like imprecise use of a term standardized by PKCS #10 and used in PKIX. Instead, use the standard term, "certification request". $ certificate revocation (I) The event that occurs when a CA declares that a previously valid digital certificate issued by that CA has become invalid; usually stated with a revocation date. (C) In X.509, a revocation is announced to potential certificate users by issuing a CRL that mentions the certificate. Revocation and listing on a CRL is only necessary before certificate expiration. $ certificate revocation list (CRL) (I) A data structure that enumerates digital certificates that have been invalidated by their issuer prior to when they were scheduled to expire. (See: certificate expiration, X.509 certificate revocation list.) (O) "A signed list indicating a set of certificates that are no longer considered valid by the certificate issuer. After a certificate appears on a CRL, it is deleted from a subsequent CRL after the certificate's expiry. CRLs may be used to identify revoked public-key certificates or attribute certificates and may represent revocation of certificates issued to authorities or to users. The term CRL is also commonly used as a generic term applying to all the different types of revocation lists, including CRLs, ARLs, ACRLs, etc." [FPDAM] $ certificate revocation tree (I) A mechanism for distributing notice of certificate revocations; uses a tree of hash results that is signed by the tree's issuer. Offers an alternative to issuing a CRL, but is not supported in X.509. (See: certificate status responder.) $ certificate serial number (I) An integer value that (a) is associated with, and may be carried in, a digital certificate; (b) is assigned to the certificate by the certificate's issuer; and (c) is unique among all the certificates produced by that issuer.