(C) The set of embedded bits (the digital watermark) is sometimes
      hidden, usually imperceptible, and always intended to be
      unobtrusive. Depending on the particular technique that is used,
      digital watermarking can assist in proving ownership, controlling
      duplication, tracing distribution, ensuring data integrity, and
      performing other functions to protect intellectual property
      rights. [ACM]

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

   $ directory
   $ Directory
      See: directory vs. Directory.

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

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

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

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

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

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

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

      (O) "A means of restricting access to objects based on the
      identity of subjects and/or groups to which they belong. The
      controls are discretionary in the sense that a subject with a
      certain access permission is capable of passing that permission
      (perhaps indirectly) on to any other subject." [DOD1]

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

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

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

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

      (C) A DN is a set of attribute values that identify the path
      leading from the base of the DIT to the object that is named. An
      X.509 public-key certificate or CRL contains a DN that identifies
      its issuer, and an X.509 attribute certificate contains a DN or
      other form of name that identifies its subject.

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

   $ distribution point
      (I) An X.500 Directory entry or other information source that is
      named in a v3 X.509 public-key certificate extension as a location
      from which to obtain a CRL that might list the certificate.

      (C) A v3 X.509 public-key certificate may have a
      "cRLDistributionPoints" extension that names places to get CRLs on
      which the certificate might be listed. A CRL obtained from a
      distribution point may (a) cover either all reasons for which a
      certificate might be revoked or only some of the reasons, (b) be
      issued by either the authority that signed the certificate or some

      other authority, and (c) contain revocation entries for only a
      subset of the full set of certificates issued by one CA or (c')
      contain revocation entries for multiple CAs.

   $ DN
      See: distinguished name.

   $ DNS
      See: Domain Name System.

   $ DOI
      See: Domain of Interpretation.

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

      (I) Internet usage: That part of the Internet domain name space
      tree [R1034] that is at or below the name the specifies the
      domain. A domain is a subdomain of another domain if it is
      contained within that domain. For example, D.C.B.A is a subdomain
      of C.B.A. (See: Domain Name System.)

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

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

   $ domain name
      (I) The style of identifier--a sequence of case-insensitive ASCII
      labels separated by dots ("bbn.com.")--defined for subtrees in the
      Internet Domain Name System [R1034] and used in other Internet
      identifiers, such as host names (e.g., "rosslyn.bbn.com."),
      mailbox names (e.g., "rshirey@bbn.com."), and URLs (e.g.,
      "http://www.rosslyn.bbn.com/foo"). (See: distinguished name,
      domain.)

      (C) The domain name space of the DNS is a tree structure in which
      each node and leaf holds records describing a resource. Each node
      has a label. The domain name of a node is the list of labels on
      the path from the node to the root of the tree. The labels in a
      domain name are printed or read left to right, from the most
      specific (lowest, farthest from the root) to the least specific
      (highest, closest to the root). The root's label is the null

      string, so a complete domain name properly ends in a dot. The top-
      level domains, those immediately below the root, include COM, EDU,
      GOV, INT, MIL, NET, ORG, and two-letter country codes (such as US)
      from ISO-3166. [R1591] (See: country code.)

   $ Domain Name System (DNS)
      (I) The main Internet operations database, which is distributed
      over a collection of servers and used by client software for
      purposes such as translating a domain name-style host name into an
      IP address (e.g., "rosslyn.bbn.com" is "192.1.7.10") and locating
      a host that accepts mail for some mailbox address. [R1034]

      (C) The DNS has three major components:

       - Domain name space and resource records: Specifications for the
         tree-structured domain name space, and data associated with the
         names.

       - Name servers: Programs that hold information about a subset of
         the tree's structure and data holdings, and also hold pointers
         to other name servers that can provide information from any
         part of the tree.

       - Resolvers: Programs that extract information from name servers
         in response to client requests; typically, system routines
         directly accessible to user programs.

      (C) Extensions to the DNS [R2065, R2137, R2536] support (a) key
      distribution for public keys needed for the DNS and for other
      protocols, (b) data origin authentication service and data
      integrity service for resource records, (c) data origin
      authentication service for transactions between resolvers and
      servers, and (d) access control of records.

   $ domain of interpretation (DOI)
      (I) IPsec usage: An ISAKMP/IKE DOI defines payload formats,
      exchange types, and conventions for naming security-relevant
      information such as security policies or cryptographic algorithms
      and modes.

      (C) For example, see [R2407]. The DOI concept is based on work by
      the TSIG's CIPSO Working Group.

   $ dominate
      (I) Security level A is said to "dominate" security level B if the
      hierarchical classification level of A is greater (higher) than or
      equal to that of B and the nonhierarchical categories of A include
      all of those of B.

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

      (C) A dongle is essentially a physical key used for copy
      protection of software, because the program will not run unless
      the matching dongle is attached. When the software runs, it
      periodically queries the dongle and quits if the dongle does not
      reply with the proper authentication information. Dongles were
      originally constructed as an EPROM (erasable programmable read-
      only memory) to be connected to a serial input-output port of a
      personal computer.

   $ downgrade
      (I) Reduce the classification level of information in an
      authorized manner.

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

   $ DSA
      See: Digital Signature Algorithm.

   $ DSS
      See: Digital Signature Standard.

   $ dual control
      (I) A procedure that uses two or more entities (usually persons)
      operating in concert to protect a system resource, such that no
      single entity acting alone can access that resource. (See: no-lone
      zone, separation of duties, split knowledge.)

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

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

      (C) Generated by hashing each message separately, concatenating
      the two hash results, and then hashing that value and encrypting
      the result with the signer's private key. Done to reduce the
      number of encryption operations and to enable verification of data
      integrity without complete disclosure of the data.

   $ EAP
      See: Extensible Authentication Protocol

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

   $ ECB
      See: electronic codebook.

   $ ECDSA
      See: Elliptic Curve Digital Signature Algorithm.

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

   $ EDI
      See: electronic data interchange.

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

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

   $ EES
      See: Escrowed Encryption Standard.

   $ El Gamal algorithm
      (N) An algorithm for asymmetric cryptography, invented in 1985 by
      Taher El Gamal, that is based on the difficulty of calculating
      discrete logarithms and can be used for both encryption and
      digital signatures. [ElGa, Schn]

   $ electronic codebook (ECB)
      (I) An block cipher mode in which a plaintext block is used
      directly as input to the encryption algorithm and the resultant
      output block is used directly as ciphertext [FP081].

   $ electronic commerce
      (I) General usage: Business conducted through paperless exchanges
      of information, using electronic data interchange, electronic
      funds transfer (EFT), electronic mail, computer bulletin boards,
      facsimile, and other paperless technologies.

      (O) SET usage: "The exchange of goods and services for payment
      between the cardholder and merchant when some or all of the
      transaction is performed via electronic communication." [SET2]

   $ electronic data interchange (EDI)
      (I) Computer-to-computer exchange, between trading partners, of
      business data in standardized document formats.

      (C) EDI formats have been standardized primarily by ANSI X12 and
      by EDIFACT (EDI for Administration, Commerce, and Transportation),
      which is an international, UN-sponsored standard primarily used in
      Europe and Asia. X12 and EDIFACT are aligning to create a single,
      global EDI standard.

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

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

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

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

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

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

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

   $ EMSEC
      See: emanations security.

   $ EMV
      (I) An abbreviation of "Europay, MasterCard, Visa". Refers to a
      specification for smart cards that are used as payment cards, and
      for related terminals and applications. [EMV1, EMV2, EMV3]

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

      (C) ESP may be used alone, or in combination with the IPsec AH
      protocol, or in a nested fashion with tunneling. Security services
      can be provided between a pair of communicating hosts, between a
      pair of communicating security gateways, or between a host and a
      gateway. The ESP header is encapsulated by the IP header, and the
      ESP header encapsulates either the upper layer protocol header
      (transport mode) or an IP header (tunnel mode). ESP can provide
      data confidentiality service, data origin authentication service,
      connectionless data integrity service, an anti-replay service, and
      limited traffic flow confidentiality. The set of services depends
      on the placement of the implementation and on options selected
      when the security association is established.

   $ encipher
      (D) ISDs SHOULD NOT use this term as a synonym for "encrypt".
      However, see the usage note under "encryption".

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

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

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

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

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

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

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

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

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

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

   $ encryption certificate
      (I) A public-key certificate that contains a public key that is
      intended to be used for encrypting data, rather than for verifying
      digital signatures or performing other cryptographic functions.

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

   $ end entity
      (I) A system entity that is the subject of a public-key
      certificate and that is using, or is permitted and able to use,
      the matching private key only for a purpose or purposes other than
      signing a digital certificate; i.e., an entity that is not a CA.

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

      (C) ISDs SHOULD NOT use the X.509 definition, because it is
      misleading and incomplete. First, the X.509 definition should say
      "private key" rather than "public key" because certificates are
      not usefully signed with a public key. Second, the X.509
      definition is weak regarding whether an end entity may or may not
      use the private key to sign a certificate, i.e., whether the
      subject may be a CA. The intent of X.509's authors was that an end
      entity certificate is not valid for use in verifying a signature
      on an X.509 certificate or X.509 CRL. Thus, it would have been
      better for the X.509 definition to have said "only for purposes
      other than signing certificates".

      (C) Despite the problems in the X.509 definition, the term itself
      is useful in describing applications of asymmetric cryptography.
      The way the term is used in X.509 implies that it was meant to be
      defined, as we have done here, relative to roles that an entity
      (which is associated with an OSI end system) is playing or is
      permitted to play in applications of asymmetric cryptography other
      than the PKI that supports applications.

      (C) Whether a subject can play both CA and non-CA roles, with
      either the same or different certificates, is a matter of policy.
      (See: certification practice statement.) A v3 X.509 public-key
      certificate may have a "basicConstraints" extension containing a
      "cA" value that specifically "indicates whether or not the public
      key may be used to verify certificate signatures".

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

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

      (C) When two points are separated by multiple communication links
      that are connected by one or more intermediate relays, end-to-end
      encryption enables the source and destination systems to protect
      their communications without depending on the intermediate systems
      to provide the protection.

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

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

   $ entity
      See: system entity.

   $ entrapment
      (I) "The deliberate planting of apparent flaws in a system for the
      purpose of detecting attempted penetrations or confusing an
      intruder about which flaws to exploit." [FP039] (See: honey pot.)

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

   $ error detection code
      (I) A checksum designed to detect, but not correct, accidental
      (i.e., unintentional) changes in data.

   $ Escrowed Encryption Standard (EES)
      (N) A U.S. Government standard [FP185] that specifies use of a
      symmetric encryption algorithm (SKIPJACK) and a Law Enforcement

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

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

   $ ESP
      See: Encapsulating Security Payload.

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

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

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

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

   $ expire
      See: certificate expiration.

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

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

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

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

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

       - "Certificate extension": X.509 defines standard extensions that
         may be included in v3 certificates to provide additional key
         and security policy information, subject and issuer attributes,
         and certification path constraints.

       - "CRL extension": X.509 defines extensions that may be included
         in v2 CRLs to provide additional issuer key and name
         information, revocation reasons and constraints, and
         information about distribution points and delta CRLs.

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

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

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

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

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

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

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

      (C) Issued under the provisions of section 111(d) of the Federal
      Property and Administrative Services Act of 1949 as amended by the
      Computer Security Act of 1987, Public Law 100-235.

   $ Federal Public-key Infrastructure (FPKI)
      (N) A PKI being planned to establish facilities, specifications,
      and policies needed by the U.S. Federal Government to use public-
      key certificates for INFOSEC, COMSEC, and electronic commerce
      involving unclassified but sensitive applications and interactions
      between Federal agencies as well as with entities of other
      branches of the Federal Government, state, and local governments,
      business, and the public. [FPKI]

   $ Federal Standard 1027
      (N) An U.S. Government document defining emanation, anti-tamper,
      security fault analysis, and manual key management criteria for
      DES encryption devices, primary for OSI layer 2. Was renamed "FIPS
      PUB 140" when responsibility for protecting unclassified,
      sensitive information was transferred from NSA to NIST, and then
      was superseded by FIPS PUB 140-1.

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

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

      (C) A filtering router may be used as a firewall or part of a
      firewall. A router usually receives a packet from a network and
      decides where to forward it on a second network. A filtering
      router does the same, but first decides whether the packet should
      be forwarded at all, according to some security policy. The policy
      is implemented by rules (packet filters) loaded into the router.
      The rules mostly involve values of data packet control fields
      (especially IP source and destination addresses and TCP port
      numbers). [R2179]

   $ financial institution
      (N) "An establishment responsible for facilitating customer-
      initiated transactions or transmission of funds for the extension
      of credit or the custody, loan, exchange, or issuance of money."
      [SET2]

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

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

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

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

   $ FIPS
      See: Federal Information Processing Standards.

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

      (C) The standard specifies four increasing levels (from "Level 1"
      to "Level 4") of requirements to cover a wide range of potential
      applications and environments. The requirements address basic
      design and documentation, module interfaces, authorized roles and
      services, physical security, software security, operating system
      security, key management, cryptographic algorithms,
      electromagnetic interference and electromagnetic compatibility
      (EMI/EMC), and self-testing. NIST and the Canadian Communication
      Security Establishment jointly certify modules.

   $ firewall
      (I) An internetwork gateway that restricts data communication
      traffic to and from one of the connected networks (the one said to
      be "inside" the firewall) and thus protects that network's system
      resources against threats from the other network (the one that is
      said to be "outside" the firewall). (See: guard, security
      gateway.)

      (C) A firewall typically protects a smaller, secure network (such
      as a corporate LAN, or even just one host) from a larger network
      (such as the Internet). The firewall is installed at the point
      where the networks connect, and the firewall applies security
      policy rules to control traffic that flows in and out of the
      protected network.

      (C) A firewall is not always a single computer. For example, a
      firewall may consist of a pair of filtering routers and one or
      more proxy servers running on one or more bastion hosts, all
      connected to a small, dedicated LAN between the two routers. The
      external router blocks attacks that use IP to break security (IP
      address spoofing, source routing, packet fragments), while proxy
      servers block attacks that would exploit a vulnerability in a
      higher layer protocol or service. The internal router blocks
      traffic from leaving the protected network except through the
      proxy servers. The difficult part is defining criteria by which
      packets are denied passage through the firewall, because a
      firewall not only needs to keep intruders out, but usually also
      needs to let authorized users in and out.

   $ firmware
      (I) Computer programs and data stored in hardware--typically in
      read-only memory (ROM) or programmable read-only memory (PROM)--
      such that the programs and data cannot be dynamically written or
      modified during execution of the programs. (See: hardware,
      software.)

   $ FIRST
      See: Forum of Incident Response and Security Teams.

   $ flaw hypothesis methodology
      (I) An evaluation or attack technique in which specifications and
      documentation for a system are analyzed to hypothesize flaws in
      the system. The list of hypothetical flaws is prioritized on the
      basis of the estimated probability that a flaw exists and,
      assuming it does, on the ease of exploiting it and the extent of
      control or compromise it would provide. The prioritized list is
      used to direct a penetration test or attack against the system.
      [NCS04]

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

   $ flow analysis
      (I) An analysis performed on a nonprocedural formal system
      specification that locates potential flows of information between
      system variables. By assigning security levels to the variables,
      the analysis can find some types of covert channels.

   $ flow control
      (I) A procedure or technique to ensure that information transfers
      within a system are not made from one security level to another
      security level, and especially not from a higher level to a lower
      level. (See: covert channel, simple security property, confinement
      property.)

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

   $ formulary
      (I) A technique for enabling a decision to grant or deny access to
      be made dynamically at the time the access is attempted, rather
      than earlier when an access control list or ticket is created.

   $ FORTEZZA(trademark)
      (N) A registered trademark of NSA, used for a family of
      interoperable security products that implement a NIST/NSA-approved
      suite of cryptographic algorithms for digital signature, hash,
      encryption, and key exchange. The products include a PC card that
      contains a CAPSTONE chip, serial port modems, server boards, smart
      cards, and software implementations.

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

      (C) FIRST was founded in 1990 and, as of September 1999, had
      nearly 70 members spanning the globe. Its mission includes:

       - Provide members with technical information, tools, methods,
         assistance, and guidance.
       - Coordinate proactive liaison activities and analytical support.
       - Encourage development of quality products and services.
       - Improve national and international information security for
         government, private industry, academia, and the individual.
       - Enhance the image and status of the CSIRT community.

   $ forward secrecy
      See: public-key forward secrecy.

   $ FPKI
      See: Federal Public-Key Infrastructure.

   $ FTP
      See: File Transfer Protocol.

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

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

   $ GCA
      See: geopolitical certificate authority.

   $ GeneralizedTime
      (N) The ASN.1 data type "GeneralizedTime" (specified in ISO 8601)
      contains a calendar date (YYYYMMDD) and a time of day, which is
      either (a) the local time, (b) the Coordinated Universal Time, or
      (c) both the local time and an offset allowing Coordinated
      Universal Time to be calculated. (See: Coordinated Universal Time,
      UTCTime.)

   $ Generic Security Service Application Program Interface (GSS-API)
      (I) An Internet Standard protocol [R2078] that specifies calling
      conventions by which an application (typically another
      communication protocol) can obtain authentication, integrity, and
      confidentiality security services independently of the underlying
      security mechanisms and technologies, thus allowing the
      application source code to be ported to different environments.

      (C) "A GSS-API caller accepts tokens provided to it by its local
      GSS-API implementation and transfers the tokens to a peer on a
      remote system; that peer passes the received tokens to its local

      GSS-API implementation for processing. The security services
      available through GSS-API in this fashion are implementable (and
      have been implemented) over a range of underlying mechanisms based
      on [symmetric] and [asymmetric cryptography]." [R2078]

   $ geopolitical certificate authority (GCA)
      (O) SET usage: In a SET certification hierarchy, an optional level
      that is certified by a BCA and that may certify cardholder CAs,
      merchant CAs, and payment gateway CAs. Using GCAs enables a brand
      to distribute responsibility for managing certificates to
      geographic or political regions, so that brand policies can vary
      between regions as needed.

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

      (D) Usage note: To improve international comprehensibility of
      Internet Standards and the Internet Standards Process, ISDs SHOULD
      NOT use "cute" synonyms for document titles. No matter how popular
      and clearly understood a nickname may be in one community, it is
      likely to cause confusion in others. For example, several other
      information system standards also are called "the Green Book". The
      following are some examples:

       - Each volume of 1992 ITU-T (at that time, CCITT) standards.
       - "PostScript Language Program Design", Adobe Systems, Addison-
         Wesley, 1988.
       - IEEE 1003.1 POSIX Operating Systems Interface.
       - "Smalltalk-80: Bits of History, Words of Advice", Glenn
         Krasner, Addison-Wesley, 1983.
       - "X/Open Compatibility Guide".
       - A particular CD-ROM format developed by Phillips.

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

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

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

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

   $ guest login
      See: anonymous login.

   $ GULS
      (I) Generic Upper Layer Security service element (ISO 11586), a
      five-part standard for the exchange of security information and
      security-transformation functions that protect confidentiality and
      integrity of application data.

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

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

   $ handle
      (I) (1.) Verb: Perform processing operations on data, such as
      receive and transmit, collect and disseminate, create and delete,
      store and retrieve, read and write, and compare. (2.) Noun: An on-
      line pseudonym, particularly one used by a cracker; derived from
      citizens band radio culture.

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

   $ hardware token
      See: token.

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

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

      (O) "A (mathematical) function which maps values from a large
      (possibly very large) domain into a smaller range. A 'good' hash
      function is such that the results of applying the function to a
      (large) set of values in the domain will be evenly distributed
      (and apparently at random) over the range." [X509]

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

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

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

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

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

   $ hierarchical PKI
      (I) A PKI architecture based on a certification hierarchy. (See:
      mesh PKI, trust-file PKI.)

   $ hierarchy management
      (I) The process of generating configuration data and issuing
      public-key certificates to build and operate a certification
      hierarchy.

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

   $ hijack attack
      (I) A form of active wiretapping in which the attacker seizes
      control of a previously established communication association.
      (See: man-in-the-middle attack, pagejacking, piggyback attack.)

   $ HMAC
      (I) A keyed hash [R2104] that can be based on any iterated
      cryptographic hash (e.g., MD5 or SHA-1), so that the cryptographic
      strength of HMAC depends on the properties of the selected
      cryptographic hash. (See: [R2202, R2403, R2404].)

      (C) Assume that H is a generic cryptographic hash in which a
      function is iterated on data blocks of length B bytes. L is the
      length of the of hash result of H. K is a secret key of length L
      <= K <= B. The values IPAD and OPAD are fixed strings used as
      inner and outer padding and defined as follows: IPAD = the byte
      0x36 repeated B times, OPAD = the byte 0x5C repeated B times. HMAC
      is computed by H(K XOR OPAD, H(K XOR IPAD, inputdata)).

      (C) The goals of HMAC are as follows:

       - To use available cryptographic hash functions without
         modification, particularly functions that perform well in
         software and for which software is freely and widely available.
       - To preserve the original performance of the selected hash
         without significant degradation.
       - To use and handle keys in a simple way.
       - To have a well-understood cryptographic analysis of the
         strength of the mechanism based on reasonable assumptions about
         the underlying hash function.
       - To enable easy replacement of the hash function in case a
         faster or stronger hash is found or required.

   $ honey pot
      (I) A system (e.g., a web server) or a system resource (e.g., a
      file on a server), that is designed to be attractive to potential
      crackers and intruders, like honey is attractive to bears. (See:
      entrapment.)

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

   $ host
      (I) General computer network usage: A computer that is attached to
      a communication subnetwork or internetwork and can use services
      provided by the network to exchange data with other attached
      systems. (See: end system.)

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

      (C) Derivation: As viewed by its users, a host "entertains"
      guests, providing application layer services or access to other
      computers attached to the network. However, even though some
      traditional peripheral service devices, such as printers, can now
      be independently connected to networks, they are not usually
      called hosts.

   $ HTML
      See: Hypertext Markup Language.

   $ HTTP
      See: Hypertext Transfer Protocol.

   $ https
      (I) When used in the first part of a URL (the part that precedes
      the colon and specifies an access scheme or protocol), this term
      specifies the use of HTTP enhanced by a security mechanism, which
      is usually SSL. (See: S-HTTP.)

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

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

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

   $ hyperlink
      (I) In hypertext or hypermedia, an information object (such as a
      word, a phrase, or an image; usually highlighted by color or
      underscoring) that points (indicates how to connect) to related
      information that is located elsewhere and can be retrieved by
      activating the link (e.g., by selecting the object with a mouse
      pointer and then clicking).

   $ hypermedia
      (I) A generalization of hypertext; any media that contain
      hyperlinks that point to material in the same or another data
      object.

   $ hypertext
      (I) A computer document, or part of a document, that contains
      hyperlinks to other documents; i.e., text that contains active
      pointers to other text. Usually written in Hypertext Markup
      Language and accessed using a web browser. (See: hypermedia.)

   $ Hypertext Markup Language (HTML)
      (I) A platform-independent system of syntax and semantics for
      adding characters to data files (particularly text files) to
      represent the data's structure and to point to related data, thus
      creating hypertext for use in the World Wide Web and other
      applications. [R1866]

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

   $ IAB
      See: Internet Architecture Board.

   $ IANA
      See: Internet Assigned Numbers Authority.

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

   $ ICMP
      See: Internet Control Message Protocol.

   $ ICMP flood
      (I) A denial of service attack that sends a host more ICMP echo
      request ("ping") packets than the protocol implementation can
      handle. (See: flooding, smurf.)

   $ ICRL
      See: indirect certificate revocation list.

   $ IDEA
      See: International Data Encryption Algorithm.

   $ identification
      (I) An act or process that presents an identifier to a system so
      that the system can recognize a system entity and distinguish it
      from other entities. (See: authentication.)

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

      (C) Given a TCP port number pair, the server returns a character
      string that identifies the owner of that connection on the
      server's system. The protocol is not intended for authorization or
      access control. At best, it provides additional auditing
      information with respect to TCP.

   $ identity-based security policy
      (I) "A security policy based on the identities and/or attributes
      of users, a group of users, or entities acting on behalf of the
      users and the resources/objects being accessed." [I7498 Part 2]
      (See: rule-based security policy.)

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

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

   $ IEEE P1363
      (N) An IEEE working group, Standard for Public-Key Cryptography,
      developing a comprehensive reference standard for asymmetric
      cryptography. Covers discrete logarithm (e.g., DSA), elliptic
      curve, and integer factorization (e.g., RSA); and covers key
      agreement, digital signature, and encryption.

   $ IESG
      See: Internet Engineering Steering Group.

   $ IETF
      See: Internet Engineering Task Force.

   $ IKE
      See: IPsec Key Exchange.

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

   $ IMAP4 AUTHENTICATE
      (I) A IMAP4 "command" (better described as a transaction type, or
      a protocol-within-a-protocol) by which an IMAP4 client optionally
      proposes a mechanism to an IMAP4 server to authenticate the client
      to the server and provide other security services. (See: POP3.)

      (C) If the server accepts the proposal, the command is followed by
      performing a challenge-response authentication protocol and,
      optionally, negotiating a protection mechanism for subsequent POP3
      interactions. The security mechanisms that are used by IMAP4
      AUTHENTICATE--including Kerberos, GSSAPI, and S/Key--are described
      in [R1731].

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

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

   $ indistinguishability
      (I) An attribute of an encryption algorithm that is a
      formalization of the notion that the encryption of some string is
      indistinguishable from the encryption of an equal-length string of
      nonsense.

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

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

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

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

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

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

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

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

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

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

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

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

   $ International Data Encryption Algorithm (IDEA)
      (N) A patented, symmetric block cipher that uses a 128-bit key and
      operates on 64-bit blocks. [Schn] (See: symmetric cryptography.)

   $ International Standard
      See: (secondary definition under) ISO.

   $ International Traffic in Arms Regulations (ITAR)
      (N) Rules issued by the U.S. State Department, by authority of the
      Arms Export Control Act (22 U.S.C. 2778), to control export and
      import of defense articles and defense services, including
      information security systems, such as cryptographic systems, and
      TEMPEST suppression technology. (See: Wassenaar Arrangement.)

   $ internet
   $ Internet
      See: internet vs. Internet.

   $ Internet Architecture Board (IAB)
      (I) A technical advisory group of the ISOC, chartered by the ISOC
      Trustees to provide oversight of Internet architecture and
      protocols and, in the context of Internet Standards, a body to
      which decisions of the IESG may be appealed. Responsible for
      approving appointments to the IESG from among nominees submitted
      by the IETF nominating committee. [R2026]

   $ Internet Assigned Numbers Authority (IANA)
      (I) From the early days of the Internet, the IANA was chartered by
      the ISOC and the U.S. Government's Federal Network Council to be
      the central coordination, allocation, and registration body for
      parameters for Internet protocols. Superseded by ICANN.

   $ Internet Control Message Protocol (ICMP)
      (I) An Internet Standard protocol [R0792] that is used to report
      error conditions during IP datagram processing and to exchange
      other information concerning the state of the IP network.

   $ Internet Corporation for Assigned Names and Numbers (ICANN)
      (I) The non-profit, private corporation that has assumed
      responsibility for the IP address space allocation, protocol
      parameter assignment, domain name system management, and root
      server system management functions formerly performed under U.S.
      Government contract by IANA and other entities.

      (C) The Internet Protocol Suite, as defined by the IETF and the
      IESG, contains numerous parameters, such as internet addresses,
      domain names, autonomous system numbers, protocol numbers, port
      numbers, management information base object identifiers, including

      private enterprise numbers, and many others. The Internet
      community requires that the values used in these parameter fields
      be assigned uniquely. ICANN makes those assignments as requested
      and maintains a registry of the current values.

      (C) ICANN was formed in October 1998, by a coalition of the
      Internet's business, technical, and academic communities. The U.S.
      Government designated ICANN to serve as the global consensus
      entity with responsibility for coordinating four key functions for
      the Internet: the allocation of IP address space, the assignment
      of protocol parameters, the management of the DNS, and the
      management of the DNS root server system.

   $ Internet Draft
      (I) A working document of the IETF, its areas, and its working
      groups. (Other groups may also distribute working documents as
      Internet Drafts.) An Internet Draft is not an archival document
      like an RFC is. Instead, an Internet Draft is a preliminary or
      working document that is valid for a maximum of six months and may
      be updated, replaced, or made obsolete by other documents at any
      time. It is inappropriate to use an Internet Draft as reference
      material or to cite it other than as "work in progress."

   $ Internet Engineering Steering Group (IESG)
      (I) The part of the ISOC responsible for technical management of
      IETF activities and administration of the Internet Standards
      Process according to procedures approved by the ISOC Trustees.
      Directly responsible for actions along the "standards track",
      including final approval of specifications as Internet Standards.
      Composed of IETF Area Directors and the IETF chairperson, who also
      chairs the IESG. [R2026]

   $ Internet Engineering Task Force (IETF)
      (I) A self-organized group of people who make contributions to the
      development of Internet technology. The principal body engaged in
      developing Internet Standards, although not itself a part of the
      ISOC. Composed of Working Groups, which are arranged into Areas
      (such as the Security Area), each coordinated by one or more Area
      Directors. Nominations to the IAB and the IESG are made by a
      committee selected at random from regular IETF meeting attendees
      who have volunteered. [R2026, R2323]

   $ Internet Message Access Protocol, version 4 (IMAP4)
      (I) An Internet protocol [R2060] by which a client workstation can
      dynamically access a mailbox on a server host to manipulate and
      retrieve mail messages that the server has received and is holding
      for the client. (See: POP3.)

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

   $ Internet Policy Registration Authority (IPRA)
      (I) An X.509-compliant CA that is the top CA of the Internet
      certification hierarchy operated under the auspices of the ISOC
      [R1422]. (See: (PEM usage under) certification hierarchy.)

   $ Internet Protocol (IP)
      (I) A Internet Standard protocol (version 4 [R0791] and version 6
      [R2460]) that moves datagrams (discrete sets of bits) from one
      computer to another across an internetwork but does not provide
      reliable delivery, flow control, sequencing, or other end-to-end
      services that TCP provides. (See: IP address, TCP/IP.)

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

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

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

      (C) The IPsec architecture specifies (a) security protocols (AH
      and ESP), (b) security associations (what they are, how they work,
      how they are managed, and associated processing), (c) key
      management (IKE), and (d) algorithms for authentication and
      encryption. The set of security services include access control
      service, connectionless data integrity service, data origin
      authentication service, protection against replays (detection of
      the arrival of duplicate datagrams, within a constrained window),
      data confidentiality service, and limited traffic flow
      confidentiality.

   $ Internet Protocol Security Option (IPSO)
      (I) Refers to one of three types of IP security options, which are
      fields that may be added to an IP datagram for the purpose of
      carrying security information about the datagram. (See: IPsec.)

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