D <- 4. Definitions -> F
E
$ e-cash
(O) Electronic cash; money that is in the form of data and can be
used as a payment mechanism on the Internet. (See: IOTP.)
Usage: IDOCs that use this term SHOULD state a definition for it
because many different types of electronic cash have been devised
with a variety of security mechanisms.
$ EAP
(I) See: Extensible Authentication Protocol.
$ EAL
(O) See: evaluation assurance level.
$ Easter egg
(O) "Hidden functionality within an application program, which
becomes activated when an undocumented, and often convoluted, set
of commands and keystrokes is entered. Easter eggs are typically
used to display the credits for the development team and [are]
intended to be non-threatening" [SP28], but Easter eggs have the
potential to contain malicious code.
Deprecated Usage: It is likely that other cultures use different
metaphors for this concept. Therefore, to avoid international
misunderstanding, IDOCs SHOULD NOT use this term. (See: Deprecated
Usage under "Green Book".)
$ eavesdropping
(I) Passive wiretapping done secretly, i.e., without the knowledge
of the originator or the intended recipients of the communication.
$ ECB
(N) See: electronic codebook.
$ ECDSA
(N) See: Elliptic Curve Digital Signature Algorithm.
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$ economy of alternatives
(I) The principle that a security mechanism should be designed to
minimize the number of alternative ways of achieving a service.
(Compare: economy of mechanism.)
$ economy of mechanism
(I) The principle that a security mechanism should be designed to
be as simple as possible, so that (a) the mechanism can be
correctly implemented and (b) it can be verified that the
operation of the mechanism enforces the system's security policy.
(Compare: economy of alternatives, least privilege.)
$ ECU
(N) See: end cryptographic unit.
$ EDI
(I) See: electronic data interchange.
$ EDIFACT
(N) See: secondary definition under "electronic data interchange".
$ EE
(D) Abbreviation of "end entity" and other terms.
Deprecated Abbreviation: IDOCs SHOULD NOT use this abbreviation;
there could be confusion among "end entity", "end-to-end
encryption", "escrowed encryption standard", and other terms.
$ EES
(O) See: Escrowed Encryption Standard.
$ effective key length
(O) "A measure of strength of a cryptographic algorithm,
regardless of actual key length." [IATF] (See: work factor.)
$ effectiveness
(O) /ITSEC/ A property of a TOE representing how well it provides
security in the context of its actual or proposed operational use.
$ El Gamal algorithm
(N) An algorithm for asymmetric cryptography, invented in 1985 by
Taher El Gamal, that is based on the difficulty of calculating
discrete logarithms and can be used for both encryption and
digital signatures. [ElGa]
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$ electronic codebook (ECB)
(N) A block cipher mode in which a plaintext block is used
directly as input to the encryption algorithm and the resultant
output block is used directly as cipher text [FP081]. (See: block
cipher, [SP38A].)
$ electronic commerce
1. (I) Business conducted through paperless exchanges of
information, using electronic data interchange, electronic funds
transfer (EFT), electronic mail, computer bulletin boards,
facsimile, and other paperless technologies.
2. (O) /SET/ "The exchange of goods and services for payment
between the cardholder and merchant when some or all of the
transaction is performed via electronic communication." [SET2]
$ electronic data interchange (EDI)
(I) Computer-to-computer exchange, between trading partners, of
business data in standardized document formats.
Tutorial: EDI formats have been standardized primarily by ANSI X12
and by EDIFACT (EDI for Administration, Commerce, and
Transportation), which is an international, UN-sponsored standard
primarily used in Europe and Asia. X12 and EDIFACT are aligning to
create a single, global EDI standard.
$ Electronic Key Management System (EKMS)
(O) "Interoperable collection of systems developed by ... the U.S.
Government to automate the planning, ordering, generating,
distributing, storing, filling, using, and destroying of
electronic keying material and the management of other types of
COMSEC material." [C4009]
$ electronic signature
(D) Synonym for "digital signature" or "digitized signature".
Deprecated Term: IDOCs SHOULD NOT use this term; there is no
current consensus on its definition. Instead, use "digital
signature", if that is what was intended
$ electronic wallet
(D) A secure container to hold, in digitized form, some sensitive
data objects that belong to the owner, such as electronic money,
authentication material, and various types of personal
information. (See: IOTP.)
Deprecated Term: IDOCs SHOULD NOT use this term. There is no
current consensus on its definition; and some uses and definitions
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may be proprietary. Meanings range from virtual wallets
implemented by data structures to physical wallets implemented by
cryptographic tokens. (See: Deprecated Usage under "Green Book".)
$ elliptic curve cryptography (ECC)
(I) A type of asymmetric cryptography based on mathematics of
groups that are defined by the points on a curve, where the curve
is defined by a quadratic equation in a finite field. [Schn]
Tutorial: ECC is based on mathematics different than that
originally used to define the Diffie-Hellman-Merkle algorithm and
the DSA, but ECC can be used to define an algorithm for key
agreement that is an analog of Diffie-Hellman-Merkle [A9063] and
an algorithm for digital signature that is an analog of DSA
[A9062]. The mathematical problem upon which ECC is based is
believed to be more difficult than the problem upon which Diffie-
Hellman-Merkle is based and, therefore, that keys for ECC can be
shorter for a comparable level of security. (See: ECDSA.)
$ Elliptic Curve Digital Signature Algorithm (ECDSA)
(N) A standard [A9062] that is the analog, in elliptic curve
cryptography, of the Digital Signature Algorithm.
$ emanation
(I) A signal (e.g., electromagnetic or acoustic) that is emitted
by a system (e.g., through radiation or conductance) as a
consequence (i.e., byproduct) of the system's operation, and that
may contain information. (See: emanations security.)
$ emanations analysis
(I) /threat action/ See: secondary definition under
"interception".
$ emanations security (EMSEC)
(I) Physical security measures to protect against data compromise
that could occur because of emanations that might be received and
read by an unauthorized party. (See: emanation, TEMPEST.)
Usage: Refers either to preventing or limiting emanations from a
system and to preventing or limiting the ability of unauthorized
parties to receive the emissions.
$ embedded cryptography
(N) "Cryptography engineered into an equipment or system whose
basic function is not cryptographic." [C4009]
$ emergency plan
(D) Synonym for "contingency plan".
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Deprecated Term: IDOCs SHOULD NOT use this term. Instead, for
neutrality and consistency of language, use "contingency plan".
$ emergency response
(O) An urgent response to a fire, flood, civil commotion, natural
disaster, bomb threat, or other serious situation, with the intent
of protecting lives, limiting damage to property, and minimizing
disruption of system operations. [FP087] (See: availability, CERT,
emergency plan.)
$ EMSEC
(I) See: emanations security.
$ EMV
(N) Abbreviation of "Europay, MasterCard, Visa". Refers to a
specification for smart cards that are used as payment cards, and
for related terminals and applications. [EMV1, EMV2, EMV3]
$ Encapsulating Security Payload (ESP)
(I) An Internet protocol [R2406, R4303] designed to provide data
confidentiality service and other security services for IP
datagrams. (See: IPsec. Compare: AH.)
Tutorial: ESP may be used alone, or in combination with AH, or in
a nested fashion with tunneling. Security services can be provided
between a pair of communicating hosts, between a pair of
communicating security gateways, or between a host and a gateway.
The ESP header is encapsulated by the IP header, and the ESP
header encapsulates either the upper-layer protocol header
(transport mode) or an IP header (tunnel mode). ESP can provide
data confidentiality service, data origin authentication service,
connectionless data integrity service, an anti-replay service, and
limited traffic-flow confidentiality. The set of services depends
on the placement of the implementation and on options selected
when the security association is established.
$ encipher
(D) Synonym for "encrypt".
Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
for "encrypt". However, see Usage note under "encryption".
$ encipherment
(D) Synonym for "encryption".
Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
for "encryption". However, see Usage note under "encryption".
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$ enclave
1. (I) A set of system resources that operate in the same security
domain and that share the protection of a single, common,
continuous security perimeter. (Compare: domain.)
2. (D) /U.S. Government/ "Collection of computing environments
connected by one or more internal networks under the control of a
single authority and security policy, including personnel and
physical security." [C4009]
Deprecated Definition: IDOCs SHOULD NOT use this term with
definition 2 because the definition applies to what is usually
called a "security domain". That is, a security domain is a set of
one or more security enclaves.
$ encode
1. (I) Use a system of symbols to represent information, which
might originally have some other representation. Example: Morse
code. (See: ASCII, BER.) (See: code, decode.)
2. (D) Synonym for "encrypt".
Deprecated Definition: IDOCs SHOULD NOT use this term as a synonym
for "encrypt"; encoding is not always meant to conceal meaning.
$ encrypt
(I) Cryptographically transform data to produce cipher text. (See:
encryption. Compare: seal.)
$ encryption
1. (I) Cryptographic transformation of data (called "plain text")
into a different form (called "cipher text") that conceals the
data's original meaning and prevents the original form from being
used. The corresponding reverse process is "decryption", a
transformation that restores encrypted data to its original form.
(See: cryptography.)
2. (O) "The cryptographic transformation of data to produce
ciphertext." [I7498-2]
Usage: For this concept, IDOCs SHOULD use the verb "to encrypt"
(and related variations: encryption, decrypt, and decryption).
However, because of cultural biases involving human burial, some
international documents (particularly ISO and CCITT standards)
avoid "to encrypt" and instead use the verb "to encipher" (and
related variations: encipherment, decipher, decipherment).
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Tutorial: Usually, the plaintext input to an encryption operation
is clear text. But in some cases, the plain text may be cipher
text that was output from another encryption operation. (See:
superencryption.)
Encryption and decryption involve a mathematical algorithm for
transforming data. Besides the data to be transformed, the
algorithm has one or more inputs that are control parameters: (a)
a key that varies the transformation and, in some cases, (b) an IV
that establishes the starting state of the algorithm.
$ encryption certificate
(I) A public-key certificate that contains a public key that is
intended to be used for encrypting data, rather than for verifying
digital signatures or performing other cryptographic functions.
Tutorial: A v3 X.509 public-key certificate may have a "keyUsage"
extension that indicates the purpose for which the certified
public key is intended. (See: certificate profile.)
$ end cryptographic unit (ECU)
1. (N) Final destination device into which a key is loaded for
operational use.
2. (N) A device that (a) performs cryptographic functions, (b)
typically is part of a larger system for which the device provides
security services, and (c), from the viewpoint of a supporting
security infrastructure such as a key management system, is the
lowest level of identifiable component with which a management
transaction can be conducted
$ end entity
1. (I) A system entity that is the subject of a public-key
certificate and that is using, or is permitted and able to use,
the matching private key only for purposes other than signing a
digital certificate; i.e., an entity that is not a CA.
2. (O) "A certificate subject [that] uses its public [sic] key for
purposes other than signing certificates." [X509]
Deprecated Definition: IDOCs SHOULD NOT use definition 2, which is
misleading and incomplete. First, that definition should have said
"private key" rather than "public key" because certificates are
not usefully signed with a public key. Second, the X.509
definition is ambiguous regarding whether an end entity may or may
not use the private key to sign a certificate, i.e., whether the
subject may be a CA. The intent of X.509's authors was that an end
entity certificate is not valid for use in verifying a signature
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on an X.509 certificate or X.509 CRL. Thus, it would have been
better for the X.509 definition to have said "only for purposes
other than signing certificates".
Usage: Despite the problems in the X.509 definition, the term
itself is useful in describing applications of asymmetric
cryptography. The way the term is used in X.509 implies that it
was meant to be defined, as we have done here, relative to roles
that an entity (which is associated with an OSI end system) is
playing or is permitted to play in applications of asymmetric
cryptography other than the PKI that supports applications.
Tutorial: Whether a subject can play both CA and non-CA roles,
with either the same or different certificates, is a matter of
policy. (See: CPS.) A v3 X.509 public-key certificate may have a
"basicConstraints" extension containing a "cA" value that
specifically "indicates whether or not the public key may be used
to verify certificate signatures". (See: certificate profile.)
$ end system
(N) /OSIRM/ A computer that implements all seven layers of the
OSIRM and may attach to a subnetwork. Usage: In the IPS context,
an end system is called a "host".
$ end-to-end encryption
(I) Continuous protection of data that flows between two points in
a network, effected by encrypting data when it leaves its source,
keeping it encrypted while it passes through any intermediate
computers (such as routers), and decrypting it only when it
arrives at the intended final destination. (See: wiretapping.
Compare: link encryption.)
Examples: A few are BLACKER, CANEWARE, IPLI, IPsec, PLI, SDNS,
SILS, SSH, SSL, TLS.
Tutorial: When two points are separated by multiple communication
links that are connected by one or more intermediate relays, end-
to-end encryption enables the source and destination systems to
protect their communications without depending on the intermediate
systems to provide the protection.
$ end user
1. (I) /information system/ A system entity, usually a human
individual, that makes use of system resources, primarily for
application purposes as opposed to system management purposes.
2. (D) /PKI/ Synonym for "end entity".
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Deprecated Definition: IDOCs SHOULD NOT use "end user" as a
synonym for "end entity", because that would mix concepts in a
potentially misleading way.
$ endorsed-for-unclassified cryptographic item (EUCI)
(O) /U.S. Government/ "Unclassified cryptographic equipment that
embodies a U.S. Government classified cryptographic logic and is
endorsed by NSA for the protection of national security
information." [C4009] (Compare: CCI, type 2 product.)
$ entity
See: system entity.
$ entrapment
(I) "The deliberate planting of apparent flaws in a system for the
purpose of detecting attempted penetrations or confusing an
intruder about which flaws to exploit." [FP039] (See: honey pot.)
$ entropy
1. (I) An information-theoretic measure (usually stated as a
number of bits) of the amount of uncertainty that an attacker
faces to determine the value of a secret. [SP63] (See: strength.)
Example: If a password is said to contain at least 20 bits of
entropy, that means that it must be as hard to find the password
as to guess a 20-bit random number.
2. (I) An information-theoretic measure (usually stated as a
number of bits) of the amount of information in a message; i.e.,
the minimum number of bits needed to encode all possible meanings
of that message. [Schn] (See: uncertainty.)
$ ephemeral
(I) /adjective/ Refers to a cryptographic key or other
cryptographic parameter or data object that is short-lived,
temporary, or used one time. (See: session key. Compare: static.)
$ erase
1. (I) Delete stored data. (See: sanitize, zeroize.)
2. (O) /U.S. Government/ Delete magnetically stored data in such a
way that the data cannot be recovered by ordinary means, but might
be recoverable by laboratory methods. [C4009] (Compare: /U.S.
Government/ purge.)
$ error detection code
(I) A checksum designed to detect, but not correct, accidental
(i.e., unintentional) changes in data.
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$ Escrowed Encryption Standard (EES)
(N) A U.S. Government standard [FP185] that specifies how to use a
symmetric encryption algorithm (SKIPJACK) and create a Law
Enforcement Access Field (LEAF) for implementing part of a key
escrow system that enables decryption of telecommunications when
interception is lawfully authorized.
Tutorial: Both SKIPJACK and the LEAF are intended for use in
equipment used to encrypt and decrypt sensitive, unclassified,
telecommunications data.
$ ESP
(I) See: Encapsulating Security Payload.
$ Estelle
(N) A language (ISO 9074-1989) for formal specification of
computer network protocols.
$ ETSI
(N) See: European Telecommunication Standards Institute.
$ EUCI
(O) See: endorsed-for-unclassified cryptographic item.
$ European Telecommunication Standards Institute (ETSI)
(N) An independent, non-profit organization, based in France, that
is officially recognized by the European Commission and
responsible for standardization of information and communication
technologies within Europe.
Tutorial: ETSI maintains the standards for a number of security
algorithms, including encryption algorithms for mobile telephone
systems in Europe.
$ evaluated system
(I) A system that has been evaluated against security criteria
(for example, against the TCSEC or against a profile based on the
Common Criteria).
$ evaluation
(I) Assessment of an information system against defined security
criteria (for example, against the TCSEC or against a profile
based on the Common Criteria). (Compare: certification.)
$ evaluation assurance level (EAL)
(N) A predefined package of assurance components that represents a
point on the Common Criteria's scale for rating confidence in the
security of information technology products and systems.
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Tutorial: The Common Criteria defines a scale of seven,
hierarchically ordered EALs for rating a TOE. From highest to
lowest, they are as follows:
- EAL7. Formally verified design and tested.
- EAL6. Semiformally verified design and tested.
- EAL5. Semiformally designed and tested.
- EAL4. Methodically designed, tested, and reviewed.
- EAL3. Methodically tested and checked.
- EAL2. Structurally tested.
- EAL1. Functionally tested.
An EAL is a consistent, baseline set of requirements. The increase
in assurance from EAL to EAL is accomplished by substituting
higher assurance components (i.e., criteria of increasing rigor,
scope, or depth) from seven assurance classes: (a) configuration
management, (b) delivery and operation, (c) development, (d)
guidance documents, (e) lifecycle support, (f) tests, and (g)
vulnerability assessment.
The EALs were developed with the goal of preserving concepts of
assurance that were adopted from earlier criteria, so that results
of previous evaluations would remain relevant. For example, EALs
levels 2-7 are generally equivalent to the assurance portions of
the TCSEC C2-A1 scale. However, this equivalency should be used
with caution. The levels do not derive assurance in the same
manner, and exact mappings do not exist.
$ expire
(I) /credential/ Cease to be valid (i.e., change from being valid
to being invalid) because its assigned lifetime has been exceeded.
(See: certificate expiration.)
$ exposure
(I) A type of threat action whereby sensitive data is directly
released to an unauthorized entity. (See: unauthorized
disclosure.)
Usage: This type of threat action includes the following subtypes:
- "Deliberate Exposure": Intentional release of sensitive data to
an unauthorized entity.
- "Scavenging": Searching through data residue in a system to
gain unauthorized knowledge of sensitive data.
- "Human error": /exposure/ Human action or inaction that
unintentionally results in an entity gaining unauthorized
knowledge of sensitive data. (Compare: corruption,
incapacitation.)
- "Hardware or software error": /exposure/ System failure that
unintentionally results in an entity gaining unauthorized
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knowledge of sensitive data. (Compare: corruption,
incapacitation.)
$ Extended Security Option
(I) See: secondary definition under "IPSO".
$ Extensible Authentication Protocol (EAP)
(I) An extension framework for PPP that supports multiple,
optional authentication mechanisms, including cleartext passwords,
challenge-response, and arbitrary dialog sequences. [R3748]
(Compare: GSS-API, SASL.)
Tutorial: EAP typically runs directly over IPS data link protocols
or OSIRM Layer 2 protocols, i.e., without requiring IP.
Originally, EAP was developed for use in PPP, by a host or router
that connects to a network server via switched circuits or dial-up
lines. Today, EAP's domain of applicability includes other areas
of network access control; it is used in wired and wireless LANs
with IEEE 802.1X, and in IPsec with IKEv2. EAP is conceptually
related to other authentication mechanism frameworks, such as SASL
and GSS-API.
$ Extensible Markup Language (XML)
(N) A version of Standard Generalized Markup Language (ISO 8879)
that separately represents a document's content and its structure.
XML was designed by W3C for use on the World Wide Web.
$ extension
(I) /protocol/ A data item or a mechanism that is defined in a
protocol to extend the protocol's basic or original functionality.
Tutorial: Many protocols have extension mechanisms, and the use of
these extension is usually optional. IP and X.509 are two examples
of protocols that have optional extensions. In IP version 4,
extensions are called "options", and some of the options have
security purposes (see: IPSO).
In X.509, certificate and CRL formats can be extended to provide
methods for associating additional attributes with subjects and
public keys and for managing a certification hierarchy:
- A "certificate extension": X.509 defines standard extensions
that may be included in v3 certificates to provide additional
key and security policy information, subject and issuer
attributes, and certification path constraints.
- A "CRL extension": X.509 defines extensions that may be
included in v2 CRLs to provide additional issuer key and name
information, revocation reasons and constraints, and
information about distribution points and delta CRLs.
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- A "private extension": Additional extensions, each named by an
OID, can be locally defined as needed by applications or
communities. (See: Authority Information Access extension, SET
private extensions.)
$ external controls
(I) /COMPUSEC/ Refers to administrative security, personnel
security, and physical security. (Compare: internal controls.)
$ extranet
(I) A computer network that an organization uses for application
data traffic between the organization and its business partners.
(Compare: intranet.)
Tutorial: An extranet can be implemented securely, either on the
Internet or using Internet technology, by constructing the
extranet as a VPN.
$ extraction resistance
(O) Ability of cryptographic equipment to resist efforts to
extract keying material directly from the equipment (as opposed to
gaining knowledge of keying material by cryptanalysis). [C4009]
$ extrusion detection
(I) Monitoring for unauthorized transfers of sensitive information
and other communications that originate inside a system's security
perimeter and are directed toward the outside; i.e., roughly the
opposite of "intrusion detection".
D <- 4. Definitions -> F