(I) The source code formats and procedures through which an
application program accesses cryptographic services, which are
defined abstractly compared to their actual implementation. For
example, see: PKCS #11, [R2628].
$ cryptographic card
(I) A cryptographic token in the form of a smart card or a PC
card.
$ cryptographic component
(I) A generic term for any system component that involves
cryptography. (See: cryptographic module.)
$ cryptographic hash
See: (secondary definition under) hash function.
$ cryptographic ignition key (CIK)
(I) A physical (usually electronic) token used to store,
transport, and protect cryptographic keys. (Sometimes abbreviated
as "crypto ignition key".)
(C) A typical use is to divide a split key between a CIK and a
cryptographic module, so that it is necessary to combine the two
to regenerate a key-encrypting key and thus activate the module
and other keys it contains.
$ cryptographic key
(I) Usually shortened to just "key". An input parameter that
varies the transformation performed by a cryptographic algorithm.
(O) "A sequence of symbols that controls the operations of
encipherment and decipherment." [I7498 Part 2]
(C) If a key value needs to be kept secret, the sequence of
symbols (usually bits) that comprise it should be random, or at
least pseudo-random, because that makes the key hard for an
adversary to guess. (See: cryptanalysis, brute force attack.)
$ Cryptographic Message Syntax (CMS)
(I) A encapsulation syntax for digital signatures, hashes, and
encryption of arbitrary messages. [R2630]
(C) CMS was derived from PKCS #7. CMS values are specified with
ASN.1 and use BER encoding. The syntax permits multiple
encapsulation with nesting, permits arbitrary attributes to be
signed along with message content, and supports a variety of
architectures for digital certificate-based key management.
$ cryptographic module
(I) A set of hardware, software, firmware, or some combination
thereof that implements cryptographic logic or processes,
including cryptographic algorithms, and is contained within the
module's cryptographic boundary, which is an explicitly defined
contiguous perimeter that establishes the physical bounds of the
module. [FP140]
$ cryptographic system
(I) A set of cryptographic algorithms together with the key
management processes that support use of the algorithms in some
application context.
(C) This "I" definition covers a wider range of algorithms than
the following "O" definition:
(O) "A collection of transformations from plaintext into
ciphertext and vice versa [which would exclude digital signature,
cryptographic hash, and key agreement algorithms], the particular
transformation(s) to be used being selected by keys. The
transformations are normally defined by a mathematical algorithm."
[X509]
$ cryptographic token
(I) A portable, user-controlled, physical device used to store
cryptographic information and possibly perform cryptographic
functions. (See: cryptographic card, token.)
(C) A smart token may implement some set of cryptographic
algorithms and may implement related algorithms and key management
functions, such as a random number generator. A smart
cryptographic token may contain a cryptographic module or may not
be explicitly designed that way.
$ cryptography
(I) The mathematical science that deals with transforming data to
render its meaning unintelligible (i.e., to hide its semantic
content), prevent its undetected alteration, or prevent its
unauthorized use. If the transformation is reversible,
cryptography also deals with restoring encrypted data to
intelligible form. (See: cryptology, steganography.)
(O) "The discipline which embodies principles, means, and methods
for the transformation of data in order to hide its information
content, prevent its undetected modification and/or prevent its
unauthorized use. . . . Cryptography determines the methods used
in encipherment and decipherment." [I7498 Part 2]
$ Cryptoki
See: (secondary definition under) PKCS #11.
$ cryptology
(I) The science that includes both cryptography and cryptanalysis,
and sometimes is said to include steganography.
$ cryptonet
(I) A group of system entities that share a secret cryptographic
key for a symmetric algorithm.
$ cryptoperiod
(I) The time span during which a particular key is authorized to
be used in a cryptographic system. (See: key management.)
(C) A cryptoperiod is usually stated in terms of calendar or clock
time, but sometimes is stated in terms of the maximum amount of
data permitted to be processed by a cryptographic algorithm using
the key. Specifying a cryptoperiod involves a tradeoff between the
cost of rekeying and the risk of successful cryptanalysis.
(C) Although we deprecate its prefix, this term is long-
established in COMPUSEC usage. (See: crypto) In the context of
certificates and public keys, "key lifetime" and "validity period"
are often used instead.
$ cryptosystem
(D) ISDs SHOULD NOT use this term as an abbreviation for
cryptographic system. (For rationale, see: crypto.)
$ CSIRT
See: computer security incident response team.
$ CSOR
See: Computer Security Objects Register.
$ cut-and-paste attack
(I) An active attack on the data integrity of ciphertext, effected
by replacing sections of ciphertext with other ciphertext, such
that the result appears to decrypt correctly but actually decrypts
to plaintext that is forged to the satisfaction of the attacker.
$ cyclic redundancy check (CRC)
(I) Sometimes called "cyclic redundancy code". A type of checksum
algorithm that is not a cryptographic hash but is used to
implement data integrity service where accidental changes to data
are expected.
$ DAC
See: Data Authentication Code, discretionary access control.
$ DASS
See: Distributed Authentication Security Service.
$ data
(I) Information in a specific physical representation, usually a
sequence of symbols that have meaning; especially a representation
of information that can be processed or produced by a computer.
$ Data Authentication Algorithm
(N) A keyed hash function equivalent to DES cipher block chaining
with IV = 0. [A9009]
(D) ISDs SHOULD NOT use the uncapitalized form of this term as a
synonym for other kinds of checksums.
$ data authentication code vs. Data Authentication Code (DAC)
1. (N) Capitalized: "The Data Authentication Code" refers to a
U.S. Government standard [FP113] for a checksum that is computed
by the Data Authentication Algorithm. (Also known as the ANSI
standard Message Authentication Code [A9009].)
2. (D) Not capitalized: ISDs SHOULD NOT use "data authentication
code" as a synonym for another kind of checksum, because this term
mixes concepts in a potentially misleading way. (See:
authentication code.) Instead, use "checksum", "error detection
code", "hash", "keyed hash", "Message Authentication Code", or
"protected checksum", depending on what is meant.
$ data compromise
(I) A security incident in which information is exposed to
potential unauthorized access, such that unauthorized disclosure,
alteration, or use of the information may have occurred. (See:
compromise.)
$ data confidentiality
(I) "The property that information is not made available or
disclosed to unauthorized individuals, entities, or processes
[i.e., to any unauthorized system entity]." [I7498 Part 2]. (See:
data confidentiality service.)
(D) ISDs SHOULD NOT use this term as a synonym for "privacy",
which is a different concept.
$ data confidentiality service
(I) A security service that protects data against unauthorized
disclosure. (See: data confidentiality.)
(D) ISDs SHOULD NOT use this term as a synonym for "privacy",
which is a different concept.
$ Data Encryption Algorithm (DEA)
(N) A symmetric block cipher, defined as part of the U.S.
Government's Data Encryption Standard. DEA uses a 64-bit key, of
which 56 bits are independently chosen and 8 are parity bits, and
maps a 64-bit block into another 64-bit block. [FP046] (See: DES,
symmetric cryptography.)
(C) This algorithm is usually referred to as "DES". The algorithm
has also been adopted in standards outside the Government (e.g.,
[A3092]).
$ data encryption key (DEK)
(I) A cryptographic key that is used to encipher application data.
(See: key-encrypting key.)
$ Data Encryption Standard (DES)
(N) A U.S. Government standard [FP046] that specifies the Data
Encryption Algorithm and states policy for using the algorithm to
protect unclassified, sensitive data. (See: AES, DEA.)
$ data integrity
(I) The property that data has not been changed, destroyed, or
lost in an unauthorized or accidental manner. (See: data integrity
service.)
(O) "The property that information has not been modified or
destroyed in an unauthorized manner." [I7498 Part 2]
(C) Deals with constancy of and confidence in data values, not
with the information that the values represent (see: correctness
integrity) or the trustworthiness of the source of the values
(see: source integrity).
$ data integrity service
(I) A security service that protects against unauthorized changes
to data, including both intentional change or destruction and
accidental change or loss, by ensuring that changes to data are
detectable. (See: data integrity.)
(C) A data integrity service can only detect a change and report
it to an appropriate system entity; changes cannot be prevented
unless the system is perfect (error-free) and no malicious user
has access. However, a system that offers data integrity service
might also attempt to correct and recover from changes.
(C) Relationship between data integrity service and authentication
services: Although data integrity service is defined separately
from data origin authentication service and peer entity
authentication service, it is closely related to them.
Authentication services depend, by definition, on companion data
integrity services. Data origin authentication service provides
verification that the identity of the original source of a
received data unit is as claimed; there can be no such
verification if the data unit has been altered. Peer entity
authentication service provides verification that the identity of
a peer entity in a current association is as claimed; there can be
no such verification if the claimed identity has been altered.
$ data origin authentication
(I) "The corroboration that the source of data received is as
claimed." [I7498 Part 2] (See: authentication.)
$ data origin authentication service
(I) A security service that verifies the identity of a system
entity that is claimed to be the original source of received data.
(See: authentication, authentication service.)
(C) This service is provided to any system entity that receives or
holds the data. Unlike peer entity authentication service, this
service is independent of any association between the originator
and the recipient, and the data in question may have originated at
any time in the past.
(C) A digital signature mechanism can be used to provide this
service, because someone who does not know the private key cannot
forge the correct signature. However, by using the signer's public
key, anyone can verify the origin of correctly signed data.
(C) This service is usually bundled with connectionless data
integrity service. (See: (relationship between data integrity
service and authentication services under) data integrity service.
$ data privacy
(D) ISDs SHOULD NOT use this term because it mix concepts in a
potentially misleading way. Instead, use either "data
confidentiality" or "privacy", depending on what is meant.
$ data security
(I) The protection of data from disclosure, alteration,
destruction, or loss that either is accidental or is intentional
but unauthorized.
(C) Both data confidentiality service and data integrity service
are needed to achieve data security.
$ datagram
(I) "A self-contained, independent entity of data carrying
sufficient information to be routed from the source to the
destination." [R1983]
$ DEA
See: Data Encryption Algorithm.
$ deception
See: (secondary definition under) threat consequence.
$ decipher
(D) ISDs SHOULD NOT use this term as a synonym for "decrypt",
except in special circumstances. (See: (usage discussion under)
encryption.)
$ decipherment
(D) ISDs SHOULD NOT use this term as a synonym for "decryption",
except in special circumstances. (See: (usage discussion under)
encryption.)
$ decode
(I) Convert encoded data back to its original form of
representation. (See: decrypt.)
(D) ISDs SHOULD NOT use this term as a synonym for "decrypt",
because that would mix concepts in a potentially misleading way.
$ decrypt
(I) Cryptographically restore ciphertext to the plaintext form it
had before encryption.
$ decryption
See: (secondary definition under) encryption.
$ dedicated security mode
(I) A mode of operation of an information system, wherein all
users have the clearance or authorization, and the need-to-know,
for all data handled by the system. In this mode, the system may
handle either a single classification level or category of
information or a range of levels and categories. [DOD2]
(C) This mode is defined formally in U.S. Department of Defense
policy regarding system accreditation, but the term is also used
outside the Defense Department and outside the Government.
$ default account
(I) A system login account (usually accessed with a user name and
password) that has been predefined in a manufactured system to
permit initial access when the system is first put into service.
(C) Sometimes, the default user name and password are the same in
each copy of the system. In any case, when the system is put into
service, the default password should immediately be changed or the
default account should be disabled.
$ degauss
(N) Apply a magnetic field to permanently remove, erase, or clear
data from a magnetic storage medium, such as a tape or disk
[NCS25]. Reduce magnetic flux density to zero by applying a
reversing magnetic field.
$ degausser
(N) An electrical device that can degauss magnetic storage media.
$ DEK
See: data encryption key.
$ delta CRL
(I) A partial CRL that only contains entries for X.509
certificates that have been revoked since the issuance of a prior,
base CRL. This method can be used to partition CRLs that become
too large and unwieldy.
$ denial of service
(I) The prevention of authorized access to a system resource or
the delaying of system operations and functions. (See:
availability, critical (resource of a system), flooding.)
$ DES
See: Data Encryption Standard.
$ dictionary attack
(I) An attack that uses a brute-force technique of successively
trying all the words in some large, exhaustive list.
(C) For example, an attack on an authentication service by trying
all possible passwords; or an attack on encryption by encrypting
some known plaintext phrase with all possible keys so that the key
for any given encrypted message containing that phrase may be
obtained by lookup.
$ Diffie-Hellman
(N) A key agreement algorithm published in 1976 by Whitfield
Diffie and Martin Hellman [DH76, R2631].
(C) Diffie-Hellman does key establishment, not encryption.
However, the key that it produces may be used for encryption, for
further key management operations, or for any other cryptography.
(C) The difficulty of breaking Diffie-Hellman is considered to be
equal to the difficulty of computing discrete logarithms modulo a
large prime. The algorithm is described in [R2631] and [Schn]. In
brief, Alice and Bob together pick large integers that satisfy
certain mathematical conditions, and then use the integers to each
separately compute a public-private key pair. They send each other
their public key. Each person uses their own private key and the
other person's public key to compute a key, k, that, because of
the mathematics of the algorithm, is the same for each of them.
Passive wiretapping cannot learn the shared k, because k is not
transmitted, and neither are the private keys needed to compute k.
However, without additional mechanisms to authenticate each party
to the other, a protocol based on the algorithm may be vulnerable
to a man-in-the-middle attack.
$ digest
See: message digest.
$ digital certificate
(I) A certificate document in the form of a digital data object (a
data object used by a computer) to which is appended a computed
digital signature value that depends on the data object. (See:
attribute certificate, capability, public-key certificate.)
(D) ISDs SHOULD NOT use this term to refer to a signed CRL or CKL.
Although the recommended definition can be interpreted to include
those items, the security community does not use the term with
those meanings.
$ digital certification
(D) ISDs SHOULD NOT use this term as a synonym for
"certification", unless the context is not sufficient to
distinguish between digital certification and another kind of
certification, in which case it would be better to use "public-key
certification" or another phrase that indicates what is being
certified.
$ digital document
(I) An electronic data object that represents information
originally written in a non-electronic, non-magnetic medium
(usually ink on paper) or is an analogue of a document of that
type.
$ digital envelope
(I) A digital envelope for a recipient is a combination of (a)
encrypted content data (of any kind) and (b) the content
encryption key in an encrypted form that has been prepared for the
use of the recipient.
(C) In ISDs, this term should be defined at the point of first use
because, although the term is defined in PKCS #7 and used in
S/MIME, it is not yet widely established.
(C) Digital enveloping is not simply a synonym for implementing
data confidentiality with encryption; digital enveloping is a
hybrid encryption scheme to "seal" a message or other data, by
encrypting the data and sending both it and a protected form of
the key to the intended recipient, so that no one other than the
intended recipient can "open" the message. In PCKS #7, it means
first encrypting the data using a symmetric encryption algorithm
and a secret key, and then encrypting the secret key using an
asymmetric encryption algorithm and the public key of the intended
recipient. In S/MIME, additional methods are defined for
conveying the content encryption key.
$ Digital ID(service mark)
(D) ISDs SHOULD NOT use this term as a synonym for "digital
certificate" because (a) it is the service mark of a commercial
firm, (b) it unnecessarily duplicates the meaning of other, well-
established terms, and (c) a certificate is not always used as
authentication information. In some contexts, however, it may be
useful to explain that the key conveyed in a public-key
certificate can be used to verify an identity and, therefore, that
the certificate can be thought of as digital identification
information. (See: identification information.)
$ digital key
(C) The adjective "digital" need not be used with "key" or
"cryptographic key", unless the context is insufficient to
distinguish the digital key from another kind of key, such as a
metal key for a door lock.
$ digital notary
(I) Analogous to a notary public. Provides a trusted date-and-time
stamp for a document, so that someone can later prove that the
document existed at a point in time. May also verify the
signature(s) on a signed document before applying the stamp. (See:
notarization.)
$ digital signature
(I) A value computed with a cryptographic algorithm and appended
to a data object in such a way that any recipient of the data can
use the signature to verify the data's origin and integrity. (See:
data origin authentication service, data integrity service,
digitized signature, electronic signature, signer.)
(I) "Data appended to, or a cryptographic transformation of, a
data unit that allows a recipient of the data unit to prove the
source and integrity of the data unit and protect against forgery,
e.g. by the recipient." [I7498 Part 2]
(C) Typically, the data object is first input to a hash function,
and then the hash result is cryptographically transformed using a
private key of the signer. The final resulting value is called the
digital signature of the data object. The signature value is a
protected checksum, because the properties of a cryptographic hash
ensure that if the data object is changed, the digital signature
will no longer match it. The digital signature is unforgeable
because one cannot be certain of correctly creating or changing
the signature without knowing the private key of the supposed
signer.
(C) Some digital signature schemes use a asymmetric encryption
algorithm (e.g., see: RSA) to transform the hash result. Thus,
when Alice needs to sign a message to send to Bob, she can use her
private key to encrypt the hash result. Bob receives both the
message and the digital signature. Bob can use Alice's public key
to decrypt the signature, and then compare the plaintext result to
the hash result that he computes by hashing the message himself.
If the values are equal, Bob accepts the message because he is
certain that it is from Alice and has arrived unchanged. If the
values are not equal, Bob rejects the message because either the
message or the signature was altered in transit.
(C) Other digital signature schemes (e.g., see: DSS) transform the
hash result with an algorithm (e.g., see: DSA, El Gamal) that
cannot be directly used to encrypt data. Such a scheme creates a
signature value from the hash and provides a way to verify the
signature value, but does not provide a way to recover the hash
result from the signature value. In some countries, such a scheme
may improve exportability and avoid other legal constraints on
usage.
$ Digital Signature Algorithm (DSA)
(N) An asymmetric cryptographic algorithm that produces a digital
signature in the form of a pair of large numbers. The signature is
computed using rules and parameters such that the identity of the
signer and the integrity of the signed data can be verified. (See:
Digital Signature Standard.)
$ Digital Signature Standard (DSS)
(N) The U.S. Government standard [FP186] that specifies the
Digital Signature Algorithm (DSA), which involves asymmetric
cryptography.
$ digital watermarking
(I) Computing techniques for inseparably embedding unobtrusive
marks or labels as bits in digital data--text, graphics, images,
video, or audio--and for detecting or extracting the marks later.
(C) The set of embedded bits (the digital watermark) is sometimes
hidden, usually imperceptible, and always intended to be
unobtrusive. Depending on the particular technique that is used,
digital watermarking can assist in proving ownership, controlling
duplication, tracing distribution, ensuring data integrity, and
performing other functions to protect intellectual property
rights. [ACM]
$ digitized signature
(D) ISDs SHOULD NOT use this term because there is no current
consensus on its definition. Although it appears to be used mainly
to refer to various forms of digitized images of handwritten
signatures, the term should be avoided because it might be
confused with "digital signature".
$ directory
$ Directory
See: directory vs. Directory.
$ Directory Access Protocol (DAP)
(N) An OSI protocol [X519] for communication between a Directory
User Agent (a client) and a Directory System Agent (a server).
(See: Lightweight Directory Access Protocol.)
$ directory vs. Directory
1. (I) Not capitalized: The term "directory" refers generically to
a database server or other system that provides information--such
as a digital certificate or CRL--about an entity whose name is
known.
2. (I) Capitalized: "Directory" refers specifically to the X.500
Directory. (See: repository.)
$ disaster plan
(D) A synonym for "contingency plan". In the interest of
consistency, ISDs SHOULD use "contingency plan" instead of
"disaster plan".
$ disclosure (i.e., unauthorized disclosure)
See: (secondary definition under) threat consequence.
$ discretionary access control (DAC)
(I) An access control service that enforces a security policy
based on the identity of system entities and their authorizations
to access system resources. (See: access control list, identity-
based security policy, mandatory access control.)
(C) This service is termed "discretionary" because an entity might
have access rights that permit the entity, by its own volition, to
enable another entity to access some resource.
(O) "A means of restricting access to objects based on the
identity of subjects and/or groups to which they belong. The
controls are discretionary in the sense that a subject with a
certain access permission is capable of passing that permission
(perhaps indirectly) on to any other subject." [DOD1]
$ disruption
See: (secondary definition under) threat consequence.
$ Distinguished Encoding Rules (DER)
(N) A subset of the Basic Encoding Rules, which gives exactly one
way to represent any ASN.1 value as an octet string [X690].
(C) Since there is more than one way to encode ASN.1 in BER, DER
is used in applications in which a unique encoding is needed, such
as when a digital signature is computed on an ASN.1 value.
$ distinguished name (DN)
(I) An identifier that uniquely represents an object in the X.500
Directory Information Tree (DIT) [X501]. (See: domain name.)
(C) A DN is a set of attribute values that identify the path
leading from the base of the DIT to the object that is named. An
X.509 public-key certificate or CRL contains a DN that identifies
its issuer, and an X.509 attribute certificate contains a DN or
other form of name that identifies its subject.
$ Distributed Authentication Security Service (DASS)
(I) An experimental Internet protocol [R1507] that uses
cryptographic mechanisms to provide strong, mutual authentication
services in a distributed environment.
$ distribution point
(I) An X.500 Directory entry or other information source that is
named in a v3 X.509 public-key certificate extension as a location
from which to obtain a CRL that might list the certificate.
(C) A v3 X.509 public-key certificate may have a
"cRLDistributionPoints" extension that names places to get CRLs on
which the certificate might be listed. A CRL obtained from a
distribution point may (a) cover either all reasons for which a
certificate might be revoked or only some of the reasons, (b) be
issued by either the authority that signed the certificate or some
other authority, and (c) contain revocation entries for only a
subset of the full set of certificates issued by one CA or (c')
contain revocation entries for multiple CAs.
$ DN
See: distinguished name.
$ DNS
See: Domain Name System.
$ DOI
See: Domain of Interpretation.
$ domain
(I) Security usage: An environment or context that is defined by a
security policy, security model, or security architecture to
include a set of system resources and the set of system entities
that have the right to access the resources. (See: domain of
interpretation, security perimeter.)
(I) Internet usage: That part of the Internet domain name space
tree [R1034] that is at or below the name the specifies the
domain. A domain is a subdomain of another domain if it is
contained within that domain. For example, D.C.B.A is a subdomain
of C.B.A. (See: Domain Name System.)
(O) MISSI usage: The domain of a MISSI CA is the set of MISSI
users whose certificates are signed by the CA.
(O) OSI usage: An administrative partition of a complex
distributed OSI system.
$ domain name
(I) The style of identifier--a sequence of case-insensitive ASCII
labels separated by dots ("bbn.com.")--defined for subtrees in the
Internet Domain Name System [R1034] and used in other Internet
identifiers, such as host names (e.g., "rosslyn.bbn.com."),
mailbox names (e.g., "rshirey@bbn.com."), and URLs (e.g.,
"http://www.rosslyn.bbn.com/foo"). (See: distinguished name,
domain.)
(C) The domain name space of the DNS is a tree structure in which
each node and leaf holds records describing a resource. Each node
has a label. The domain name of a node is the list of labels on
the path from the node to the root of the tree. The labels in a
domain name are printed or read left to right, from the most
specific (lowest, farthest from the root) to the least specific
(highest, closest to the root). The root's label is the null
string, so a complete domain name properly ends in a dot. The top-
level domains, those immediately below the root, include COM, EDU,
GOV, INT, MIL, NET, ORG, and two-letter country codes (such as US)
from ISO-3166. [R1591] (See: country code.)
$ Domain Name System (DNS)
(I) The main Internet operations database, which is distributed
over a collection of servers and used by client software for
purposes such as translating a domain name-style host name into an
IP address (e.g., "rosslyn.bbn.com" is "192.1.7.10") and locating
a host that accepts mail for some mailbox address. [R1034]
(C) The DNS has three major components:
- Domain name space and resource records: Specifications for the
tree-structured domain name space, and data associated with the
names.
- Name servers: Programs that hold information about a subset of
the tree's structure and data holdings, and also hold pointers
to other name servers that can provide information from any
part of the tree.
- Resolvers: Programs that extract information from name servers
in response to client requests; typically, system routines
directly accessible to user programs.
(C) Extensions to the DNS [R2065, R2137, R2536] support (a) key
distribution for public keys needed for the DNS and for other
protocols, (b) data origin authentication service and data
integrity service for resource records, (c) data origin
authentication service for transactions between resolvers and
servers, and (d) access control of records.
$ domain of interpretation (DOI)
(I) IPsec usage: An ISAKMP/IKE DOI defines payload formats,
exchange types, and conventions for naming security-relevant
information such as security policies or cryptographic algorithms
and modes.
(C) For example, see [R2407]. The DOI concept is based on work by
the TSIG's CIPSO Working Group.
$ dominate
(I) Security level A is said to "dominate" security level B if the
hierarchical classification level of A is greater (higher) than or
equal to that of B and the nonhierarchical categories of A include
all of those of B.
$ dongle
(I) A portable, physical, electronic device that is required to be
attached to a computer to enable a particular software program to
run. (See: token.)
(C) A dongle is essentially a physical key used for copy
protection of software, because the program will not run unless
the matching dongle is attached. When the software runs, it
periodically queries the dongle and quits if the dongle does not
reply with the proper authentication information. Dongles were
originally constructed as an EPROM (erasable programmable read-
only memory) to be connected to a serial input-output port of a
personal computer.
$ downgrade
(I) Reduce the classification level of information in an
authorized manner.
$ draft RFC
(D) ISDs SHOULD NOT use this term, because the Request for Comment
series is archival in nature and does not have a "draft" category.
(Instead, see: Internet Draft, Draft Standard (in Internet
Standard).)
$ DSA
See: Digital Signature Algorithm.
$ DSS
See: Digital Signature Standard.
$ dual control
(I) A procedure that uses two or more entities (usually persons)
operating in concert to protect a system resource, such that no
single entity acting alone can access that resource. (See: no-lone
zone, separation of duties, split knowledge.)
$ dual signature
(D) ISDs SHOULD NOT use this term except when stated as
"SET(trademark) dual signature" with the following meaning:
(O) SET usage: A single digital signature that protects two
separate messages by including the hash results for both sets in a
single encrypted value. [SET2]
(C) Generated by hashing each message separately, concatenating
the two hash results, and then hashing that value and encrypting
the result with the signer's private key. Done to reduce the
number of encryption operations and to enable verification of data
integrity without complete disclosure of the data.
$ EAP
See: Extensible Authentication Protocol
$ eavesdropping
(I) Passive wiretapping done secretly, i.e., without the knowledge
of the originator or the intended recipients of the communication.
$ ECB
See: electronic codebook.
$ ECDSA
See: Elliptic Curve Digital Signature Algorithm.
$ economy of mechanism
(I) The principle that each security mechanism should be designed
to be as simple as possible, so that the mechanism can be
correctly implemented and so that it can be verified that the
operation of the mechanism enforces the containing system's
security policy. (See: least privilege.)
$ EDI
See: electronic data interchange.
$ EDIFACT
See: (secondary definition under) electronic data interchange.
$ EE
(D) ISDs SHOULD NOT use this abbreviation because of possible
confusion among "end entity", "end-to-end encryption", "escrowed
encryption standard", and other terms.
$ EES
See: Escrowed Encryption Standard.
$ El Gamal algorithm
(N) An algorithm for asymmetric cryptography, invented in 1985 by
Taher El Gamal, that is based on the difficulty of calculating
discrete logarithms and can be used for both encryption and
digital signatures. [ElGa, Schn]
$ electronic codebook (ECB)
(I) An block cipher mode in which a plaintext block is used
directly as input to the encryption algorithm and the resultant
output block is used directly as ciphertext [FP081].
$ electronic commerce
(I) General usage: Business conducted through paperless exchanges
of information, using electronic data interchange, electronic
funds transfer (EFT), electronic mail, computer bulletin boards,
facsimile, and other paperless technologies.
(O) SET usage: "The exchange of goods and services for payment
between the cardholder and merchant when some or all of the
transaction is performed via electronic communication." [SET2]
$ electronic data interchange (EDI)
(I) Computer-to-computer exchange, between trading partners, of
business data in standardized document formats.
(C) EDI formats have been standardized primarily by ANSI X12 and
by EDIFACT (EDI for Administration, Commerce, and Transportation),
which is an international, UN-sponsored standard primarily used in
Europe and Asia. X12 and EDIFACT are aligning to create a single,
global EDI standard.
$ electronic signature
(D) ISDs SHOULD NOT use this term because there is no current
consensus on its definition. (Instead, see: digital signature.)
$ elliptic curve cryptography (ECC)
(I) A type of asymmetric cryptography based on mathematics of
groups that are defined by the points on a curve.
(C) The most efficient implementation of ECC is claimed to be
stronger per bit of key (against cryptanalysis that uses a brute
force attack) than any other known form of asymmetric
cryptography. ECC is based on mathematics different than the kinds
originally used to define the Diffie-Hellman algorithm and the
Digital Signature Algorithm. ECC is based on the mathematics of
groups defined by the points on a curve, where the curve is
defined by a quadratic equation in a finite field. ECC can be used
to define both an algorithm for key agreement that is an analog of
Diffie-Hellman and an algorithm for digital signature that is an
analog of DSA. (See: ECDSA.)
$ Elliptic Curve Digital Signature Algorithm (ECDSA)
(N) A standard [A9062] that is the elliptic curve cryptography
analog of the Digital Signature Algorithm.
$ emanation
(I) An signal (electromagnetic, acoustic, or other medium) that is
emitted by a system (through radiation or conductance) as a
consequence (i.e., byproduct) of its operation, and that may
contain information. (See: TEMPEST.)
$ emanations security (EMSEC)
(I) Physical constraints to prevent information compromise through
signals emanated by a system, particular the application of
TEMPEST technology to block electromagnetic radiation.
$ emergency plan
(D) A synonym for "contingency plan". In the interest of
consistency, ISDs SHOULD use "contingency plan" instead of
"emergency plan".
$ EMSEC
See: emanations security.
$ EMV
(I) An abbreviation of "Europay, MasterCard, Visa". Refers to a
specification for smart cards that are used as payment cards, and
for related terminals and applications. [EMV1, EMV2, EMV3]
$ Encapsulating Security Payload (ESP)
(I) An Internet IPsec protocol [R2406] designed to provide a mix
of security services--especially data confidentiality service--in
the Internet Protocol. (See: Authentication Header.)
(C) ESP may be used alone, or in combination with the IPsec AH
protocol, or in a nested fashion with tunneling. Security services
can be provided between a pair of communicating hosts, between a
pair of communicating security gateways, or between a host and a
gateway. The ESP header is encapsulated by the IP header, and the
ESP header encapsulates either the upper layer protocol header
(transport mode) or an IP header (tunnel mode). ESP can provide
data confidentiality service, data origin authentication service,
connectionless data integrity service, an anti-replay service, and
limited traffic flow confidentiality. The set of services depends
on the placement of the implementation and on options selected
when the security association is established.
$ encipher
(D) ISDs SHOULD NOT use this term as a synonym for "encrypt".
However, see the usage note under "encryption".
$ encipherment
(D) ISDs SHOULD NOT use this term as a synonym for "encryption",
except in special circumstances that are explained in the usage
discussion under "encryption".
$ encode
(I) Use a system of symbols to represent information, which might
originally have some other representation. (See: decode.)
(C) Examples include Morse code, ASCII, and BER.
(D) ISDs SHOULD NOT use this term as a synonym for "encrypt",
because encoding is not usually intended to conceal meaning.
$ encrypt
(I) Cryptographically transform data to produce ciphertext. (See:
encryption.)
$ encryption
(I) Cryptographic transformation of data (called "plaintext") into
a form (called "ciphertext") that conceals the data's original
meaning to prevent it from being known or used. If the
transformation is reversible, the corresponding reversal process
is called "decryption", which is a transformation that restores
encrypted data to its original state. (See: cryptography.)
(C) Usage note: For this concept, ISDs should use the verb "to
encrypt" (and related variations: encryption, decrypt, and
decryption). However, because of cultural biases, some
international usage, particularly ISO and CCITT standards, avoids
"to encrypt" and instead uses the verb "to encipher" (and related
variations: encipherment, decipher, decipherment).
(O) "The cryptographic transformation of data (see: cryptography)
to produce ciphertext." [I7498 Part 2]
(C) Usually, the plaintext input to an encryption operation is
cleartext. But in some cases, the plaintext may be ciphertext that
was output from another encryption operation. (See:
superencryption.)
(C) Encryption and decryption involve a mathematical algorithm for
transforming data. In addition to the data to be transformed, the
algorithm has one or more inputs that are control parameters: (a)
a key value that varies the transformation and, in some cases, (b)
an initialization value that establishes the starting state of the
algorithm.
$ encryption certificate
(I) A public-key certificate that contains a public key that is
intended to be used for encrypting data, rather than for verifying
digital signatures or performing other cryptographic functions.
C) A v3 X.509 public-key certificate may have a "keyUsage"
extension that indicates the purpose for which the certified
public key is intended.
$ end entity
(I) A system entity that is the subject of a public-key
certificate and that is using, or is permitted and able to use,
the matching private key only for a purpose or purposes other than
signing a digital certificate; i.e., an entity that is not a CA.
(D) "A certificate subject which uses its public [sic] key for
purposes other than signing certificates." [X509]
(C) ISDs SHOULD NOT use the X.509 definition, because it is
misleading and incomplete. First, the X.509 definition should say
"private key" rather than "public key" because certificates are
not usefully signed with a public key. Second, the X.509
definition is weak regarding whether an end entity may or may not
use the private key to sign a certificate, i.e., whether the
subject may be a CA. The intent of X.509's authors was that an end
entity certificate is not valid for use in verifying a signature
on an X.509 certificate or X.509 CRL. Thus, it would have been
better for the X.509 definition to have said "only for purposes
other than signing certificates".
(C) Despite the problems in the X.509 definition, the term itself
is useful in describing applications of asymmetric cryptography.
The way the term is used in X.509 implies that it was meant to be
defined, as we have done here, relative to roles that an entity
(which is associated with an OSI end system) is playing or is
permitted to play in applications of asymmetric cryptography other
than the PKI that supports applications.
(C) Whether a subject can play both CA and non-CA roles, with
either the same or different certificates, is a matter of policy.
(See: certification practice statement.) A v3 X.509 public-key
certificate may have a "basicConstraints" extension containing a
"cA" value that specifically "indicates whether or not the public
key may be used to verify certificate signatures".
$ end system
(I) An OSI term for a computer that implements all seven layers of
the OSIRM and may attach to a subnetwork. (In the context of the
Internet Protocol Suite, usually called a "host".)
$ end-to-end encryption
(I) Continuous protection of data that flows between two points in
a network, provided by encrypting data when it leaves its source,
leaving it encrypted while it passes through any intermediate
computers (such as routers), and decrypting only when the data
arrives at the intended destination. (See: link encryption,
wiretapping.)
(C) When two points are separated by multiple communication links
that are connected by one or more intermediate relays, end-to-end
encryption enables the source and destination systems to protect
their communications without depending on the intermediate systems
to provide the protection.
$ end user
(I) General usage: A system entity, usually a human individual,
that makes use of system resources, primarily for application
purposes as opposed to system management purposes.
(I) PKI usage: A synonym for "end entity"; but the term "end
entity" is preferred.
$ entity
See: system entity.
$ entrapment
(I) "The deliberate planting of apparent flaws in a system for the
purpose of detecting attempted penetrations or confusing an
intruder about which flaws to exploit." [FP039] (See: honey pot.)
$ ephemeral key
(I) A public key or a private key that is relatively short-lived.
(See: session key.)
$ error detection code
(I) A checksum designed to detect, but not correct, accidental
(i.e., unintentional) changes in data.
$ Escrowed Encryption Standard (EES)
(N) A U.S. Government standard [FP185] that specifies use of a
symmetric encryption algorithm (SKIPJACK) and a Law Enforcement
Access Field (LEAF) creation method to implement part of a key
escrow system that provides for decryption of encrypted
telecommunications when interception is lawfully authorized.
(C) Both SKIPJACK and the LEAF are to be implemented in equipment
used to encrypt and decrypt unclassified, sensitive
telecommunications data.
$ ESP
See: Encapsulating Security Payload.
$ Estelle
(N) A language (ISO 9074-1989) for formal specification of
computer network protocols.
$ evaluated products list
(O) General usage: A list of information system equipment items
that have been evaluated against, and found to be compliant with,
a particular set of criteria.
(O) U.S. Department of Defense usage: The Evaluated Products List
(http://www.radium.ncsc.mil/tpep/epl/) contains items that have
been evaluated against the TCSEC by the NCSC, or against the
Common Criteria by the NCSC or one of its partner agencies in
another county. The List forms Chapter 4 of NSA's "Information
Systems Security Products and Services Catalogue".
$ evaluated system
(I) Refers to a system that has been evaluated against security
criteria such as the TCSEC or the Common Criteria.
$ expire
See: certificate expiration.
$ exposure
See: (secondary definition under) threat consequence.
$ Extensible Authentication Protocol
(I) A framework that supports multiple, optional authentication
mechanisms for PPP, including cleartext passwords, challenge-
response, and arbitrary dialog sequences. [R2284]
(C) This protocol is intended for use primarily by a host or
router that connects to a PPP network server via switched circuits
or dial-up lines.
$ extension
(I) A data item defined for optional inclusion in a v3 X.509
public-key certificate or a v2 X.509 CRL.
(C) The formats defined in X.509 can be extended to provide
methods for associating additional attributes with subjects and
public keys and for managing a certification hierarchy:
- "Certificate extension": X.509 defines standard extensions that
may be included in v3 certificates to provide additional key
and security policy information, subject and issuer attributes,
and certification path constraints.
- "CRL extension": X.509 defines extensions that may be included
in v2 CRLs to provide additional issuer key and name
information, revocation reasons and constraints, and
information about distribution points and delta CRLs.
- "Private extension": Additional extensions, each named by an
OID, can be locally defined as needed by applications or
communities. (See: PKIX private extension, SET private
extensions.)
$ extranet
(I) A computer network that an organization uses to carry
application data traffic between the organization and its business
partners. (See: intranet.)
(C) An extranet can be implemented securely, either on the
Internet or using Internet technology, by constructing the
extranet as a VPN.
$ fail safe
(I) A mode of system termination that automatically leaves system
processes and components in a secure state when a failure occurs
or is detected in the system.
$ fail soft
(I) Selective termination of affected non-essential system
functions and processes when a failure occurs or is detected in
the system.
$ failure control