(O) A symbol or process adopted or executed by a system entity
with present intention to declare that a data object is genuine.
(See: digital signature, electronic signature.)
$ signature certificate
(I) A public-key certificate that contains a public key that is
intended to be used for verifying digital signatures, rather than
for encrypting data 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.)
$ signed receipt
(I) An S/MIME service [R2634] that (a) provides, to the originator
of a message, proof of delivery of the message and (b) enables the
originator to demonstrate to a third party that the recipient was
able to verify the signature of the original message.
Tutorial: The receipt is bound to the original message by a
signature; consequently, the service may be requested only for a
message that is signed. The receipt sender may optionally also
encrypt the receipt to provide confidentiality between the receipt
sender and the receipt recipient.
(N) A human being or organization entity that uses a private key
to sign (i.e., create a digital signature on) a data object. [DSG]
(N) See: Standards for Interoperable LAN/MAN Security.
$ simple authentication
1. (I) An authentication process that uses a password as the
information needed to verify an identity claimed for an entity.
(Compare: strong authentication.)
2. (O) "Authentication by means of simple password arrangements."
$ Simple Authentication and Security Layer (SASL)
(I) An Internet specification [R2222, R4422] for adding
authentication service to connection-based protocols. (Compare:
Tutorial: To use SASL, a protocol includes a command for
authenticating a user to a server and for optionally negotiating
protection of subsequent protocol interactions. The command names
a registered security mechanism. SASL mechanisms include Kerberos,
GSS-API, S/KEY, and others. Some protocols that use SASL are IMAP4
$ Simple Key Management for Internet Protocols (SKIP)
(I) A key-distribution protocol that uses hybrid encryption to
convey session keys that are used to encrypt data in IP packets.
(See: SKIP reference in [R2356].)
Tutorial: SKIP was designed by Ashar Aziz and Whitfield Diffie at
Sun Microsystems and proposed as the standard key management
protocol for IPsec, but IKE was chosen instead. Although IKE is
mandatory for an IPsec implementation, the use of SKIP is not
SKIP uses the Diffie-Hellman-Merkle algorithm (or could use
another key-agreement algorithm) to generate a key-encrypting key
for use between two entities. A session key is used with a
symmetric algorithm to encrypt data in one or more IP packets that
are to be sent from one entity to the other. A symmetric KEK is
established and used to encrypt the session key, and the encrypted
session key is placed in a SKIP header that is added to each IP
packet that is encrypted with that session key.
$ Simple Mail Transfer Protocol (SMTP)
(I) A TCP-based, Application-Layer, Internet Standard protocol
(RFC 821) for moving electronic mail messages from one computer to
$ Simple Network Management Protocol (SNMP)
(I) A (usually) UDP-based, Application-Layer, Internet Standard
protocol (RFCs 3410-3418) for conveying management information
between system components that act as managers and agents.
$ Simple Public Key Infrastructure (SPKI)
(I) A set of experimental concepts (RFCs 2692, 2693) that were
proposed as alternatives to the concepts standardized in PKIX.
$ simple security property
(N) /formal model/ Property of a system whereby a subject has read
access to an object only if the clearance of the subject dominates
the classification of the object. See: Bell-LaPadula model.
$ single sign-on
1. (I) An authentication subsystem that enables a user to access
multiple, connected system components (such as separate hosts on a
network) after a single login at only one of the components. (See:
2. (O) /Liberty Alliance/ A security subsystem that enables a user
identity to be authenticated at an identity provider -- i.e., at a
service that authenticates and asserts the user's identity -- and
then have that authentication be honored by other service
Tutorial: A single sign-on subsystem typically requires a user to
log in once at the beginning of a session, and then during the
session transparently grants access by the user to multiple,
separately protected hosts, applications, or other system
resources, without further login action by the user (unless, of
course, the user logs out). Such a subsystem has the advantages of
being user friendly and enabling authentication to be managed
consistently across an entire enterprise. Such a subsystem also
has the disadvantage of requiring all the accessed components to
depend on the security of the same authentication information.
$ singular identity
(I) See: secondary definition under "identity".
(I) A facility -- i.e., a physical space, room, or building
together with its physical, personnel, administrative, and other
safeguards -- in which system functions are performed. (See:
(I) See: security situation.
(I) A key-distribution protocol from which features were adapted
for IKE. [SKEME]
(I) See: Simple Key Management for Internet Protocols.
(N) A type 2, 64-bit block cipher [SKIP, R2773] with a key size of
80 bits. (See: CAPSTONE, CLIPPER, FORTEZZA, Key Exchange
Tutorial: SKIPJACK was developed by NSA and formerly classified at
the U.S. DoD "Secret" level. On 23 June 1998, NSA announced that
SKIPJACK had been declassified.
(O) /MISSI/ One of the FORTEZZA PC card storage areas that are
each able to hold an X.509 certificate plus other data, including
the private key that is associated with a public-key certificate.
$ smart card
(I) A credit-card sized device containing one or more integrated
circuit chips that perform the functions of a computer's central
processor, memory, and input/output interface. (See: PC card,
Usage: Sometimes this term is used rather strictly to mean a card
that closely conforms to the dimensions and appearance of the kind
of plastic credit card issued by banks and merchants. At other
times, the term is used loosely to include cards that are larger
than credit cards, especially cards that are thicker, such as PC
$ smart token
(I) A device that conforms to the definition of "smart card"
except that rather than having the standard dimensions of a credit
card, the token is packaged in some other form, such as a military
dog tag or a door key. (See: smart card, cryptographic token.)
(I) See: security management infrastructure.
(I) See: Simple Mail Transfer Protocol.
$ smurf attack
(D) /slang/ A denial-of-service attack that uses IP broadcast
addressing to send ICMP ping packets with the intent of flooding a
system. (See: fraggle attack, ICMP flood.)
Deprecated Term: It is likely that other cultures use different
metaphors for this concept. Therefore, to avoid international
misunderstanding, IDOCs SHOULD NOT use this term.
Derivation: The Smurfs are a fictional race of small, blue
creatures that were created by a cartoonist. Perhaps the inventor
of this attack thought that a swarm of ping packets resembled a
gang of smurfs. (See: Deprecated Usage under "Green Book".)
Tutorial: The attacker sends ICMP echo request ("ping") packets
that appear to originate not from the attacker's own IP address,
but from the address of the host or router that is the target of
the attack. Each packet is addressed to an IP broadcast address,
e.g., to all IP addresses in a given network. Thus, each echo
request that is sent by the attacker results in many echo
responses being sent to the target address. This attack can
disrupt service at a particular host, at the hosts that depend on
a particular router, or in an entire network.
$ sneaker net
(D) /slang/ A process that transfers data between systems only
manually, under human control; i.e., a data transfer process that
involves an air gap.
Deprecated Term: It is likely that other cultures use different
metaphors for this concept. Therefore, to avoid international
misunderstanding, IDOCs SHOULD NOT use this term.
(N) A public-domain, cryptographic hash function (a.k.a. "The
Xerox Secure Hash Function") designed by Ralph C. Merkle at Xerox
Corporation. Snefru can produce either a 128-bit or 256-bit output
(i.e., hash result). [Schn] (See: Khafre, Khufu.)
(D) /slang/ Synonym for "passive wiretapping"; most often refers
to capturing and examining the data packets carried on a LAN.
(See: password sniffing.)
Deprecated Term: IDOCs SHOULD NOT use this term; it unnecessarily
duplicates the meaning of a term that is better established. (See:
Deprecated Usage under "Green Book".
(I) See: Simple Network Management Protocol.
$ social engineering
(D) Euphemism for non-technical or low-technology methods, often
involving trickery or fraud, that are used to attack information
systems. Example: phishing.
Deprecated Term: IDOCs SHOULD NOT use this term; it is too vague.
Instead, use a term that is specific with regard to the means of
attack, e.g., blackmail, bribery, coercion, impersonation,
intimidation, lying, or theft.
(I) An Internet protocol [R1928] that provides a generalized proxy
server that enables client-server applications (e.g., TELNET, FTP,
or HTTP; running over either TCP or UDP) to use the services of a
Tutorial: SOCKS is layered under the IPS Application Layer and
above the Transport Layer. When a client inside a firewall wishes
to establish a connection to an object that is reachable only
through the firewall, it uses TCP to connect to the SOCKS server,
negotiates with the server for the authentication method to be
used, authenticates with the chosen method, and then sends a relay
request. The SOCKS server evaluates the request, typically based
on source and destination addresses, and either establishes the
appropriate connection or denies it.
$ soft TEMPEST
(O) The use of software techniques to reduce the radio frequency
information leakage from computer displays and keyboards. [Kuhn]
$ soft token
(D) A data object that is used to control access or authenticate
authorization. (See: token.)
Deprecated Term: IDOCs SHOULD NOT use this term as defined here;
the definition duplicates the meaning of other, standard terms.
Instead, use "attribute certificate" or another term that is
specific with regard to the mechanism being used.
(I) Computer programs (which are stored in and executed by
computer hardware) and associated data (which also is stored in
the hardware) that may be dynamically written or modified during
execution. (Compare: firmware.)
$ software error
(I) /threat action/ See: secondary definitions under "corruption",
"exposure", and "incapacitation".
(O) See: SSO-PIN ORA.
$ source authentication
(D) Synonym for "data origin authentication" or "peer entity
authentication". (See: data origin authentication, peer entity
Deprecated Term: IDOCs SHOULD NOT use this term because it is
ambiguous and, in either meaning, duplicates the meaning of
internationally standardized terms. If the intent is to
authenticate the original creator or packager of data received,
then use "data origin authentication". If the intent is to
authenticate the identity of the sender of data in the current
instance, then use "peer entity authentication".
$ source integrity
(I) The property that data is trustworthy (i.e., worthy of
reliance or trust), based on the trustworthiness of its sources
and the trustworthiness of any procedures used for handling data
in the system. Usage: a.k.a. Biba integrity. (See: integrity.
Compare: correctness integrity, data integrity.)
Tutorial: For this kind of integrity, there are formal models of
unauthorized modification (see: Biba model) that logically
complement the more familiar models of unauthorized disclosure
(see: Bell-LaPadula model). In these models, objects are labeled
to indicate the credibility of the data they contain, and there
are rules for access control that depend on the labels.
(O) See: Security Protocol 3.
(O) See: Security Protocol 4.
1a. (I) /slang verb/ To indiscriminately send unsolicited,
unwanted, irrelevant, or inappropriate messages, especially
commercial advertising in mass quantities.
1b. (I) /slang noun/ Electronic "junk mail". [R2635]
Deprecated Usage: IDOCs SHOULD NOT use this term in uppercase
letters, because SPAM(trademark) is a trademark of Hormel Foods
Corporation. Hormel says, "We do not object to use of this slang
term [spam] to describe [unsolicited advertising email], although
we do object to the use of our product image in association with
that term. Also, if the term is to be used, it SHOULD be used in
all lower-case letters to distinguish it from our trademark SPAM,
which SHOULD be used with all uppercase letters." (See: metadata.)
Tutorial: In sufficient volume, spam can cause denial of service.
(See: flooding.) According to Hormel, the term was adopted as a
result of a Monty Python skit in which a group of Vikings sang a
chorus of 'SPAM, SPAM, SPAM ...' in an increasing crescendo,
drowning out other conversation. This lyric became a metaphor for
the unsolicited advertising messages that threaten to overwhelm
other discourse on the Internet.
(I) See: Security Policy Database.
$ special access program (SAP)
(O) /U.S. Government/ "Sensitive program, [that is] approved in
writing by a head of agency with [i.e., who has] original top
secret classification authority, [and] that imposes need-to-know
and access controls beyond those normally provided for access to
Confidential, Secret, or Top Secret information. The level of
controls is based on the criticality of the program and the
assessed hostile intelligence threat. The program may be an
acquisition program, an intelligence program, or an operations and
support program." [C4009] (See: formal access approval, SCI.
Compare: collateral information.)
(I) See: Security Parameters Index.
(I) See: Simple Public Key Infrastructure.
$ split key
(I) A cryptographic key that is generated and distributed as two
or more separate data items that individually convey no knowledge
of the whole key that results from combining the items. (See: dual
control, split knowledge.)
$ split knowledge
1. (I) A security technique in which two or more entities
separately hold data items that individually do not convey
knowledge of the information that results from combining the
items. (See: dual control, split key.)
2. (O) "A condition under which two or more entities separately
have key components [that] individually convey no knowledge of the
plaintext key [that] will be produced when the key components are
combined in the cryptographic module." [FP140]
(I) /threat action/ See: secondary definition under "masquerade".
$ spoofing attack
(I) Synonym for "masquerade attack".
$ spread spectrum
(N) A TRANSEC technique that transmits a signal in a bandwidth
much greater than the transmitted information needs. [F1037]
Example: frequency hopping.
Tutorial: Usually uses a sequential, noise-like signal structure
to spread the normally narrowband information signal over a
relatively wide band of frequencies. The receiver correlates the
signals to retrieve the original information signal. This
technique decreases potential interference to other receivers,
while achieving data confidentiality and increasing immunity of
spread spectrum receivers to noise and interference.
(D) /slang/ Software that an intruder has installed
surreptitiously on a networked computer to gather data from that
computer and send it through the network to the intruder or some
other interested party. (See: malicious logic, Trojan horse.)
Deprecated Usage: IDOCs that use this term SHOULD state a
definition for it because the term is used in many ways and could
easily be misunderstood.
Tutorial: Some examples of the types of data that might be
gathered by spyware are application files, passwords, email
addresses, usage histories, and keystrokes. Some examples of
motivations for gathering the data are blackmail, financial fraud,
identity theft, industrial espionage, market research, and
(N) See: Secure Shell(trademark).
(I) See: Secure Sockets Layer.
(I) See: system security officer.
$ SSO PIN
(O) /MISSI/ One of two PINs that control access to the functions
and stored data of a FORTEZZA PC card. Knowledge of the SSO PIN
enables a card user to perform the FORTEZZA functions intended for
use by an end user and also the functions intended for use by a
MISSI CA. (See: user PIN.)
$ SSO-PIN ORA (SORA)
(O) /MISSI/ A MISSI organizational RA that operates in a mode in
which the ORA performs all card management functions and,
therefore, requires knowledge of the SSO PIN for FORTEZZA PC cards
issued to end users.
$ Standards for Interoperable LAN/MAN Security (SILS)
1. (N) The IEEE 802.10 standards committee. (See: [FP191].)
2. (N) A set of IEEE standards, which has eight parts: (a) Model,
including security management, (b) Secure Data Exchange protocol,
(c) Key Management, (d) [has been incorporated in (a)], (e) SDE
Over Ethernet 2.0, (f) SDE Sublayer Management, (g) SDE Security
Labels, and (h) SDE PICS Conformance. Parts b, e, f, g, and h are
incorporated in IEEE Standard 802.10-1998.
$ star property
(N) See: *-property.
$ Star Trek attack
(D) /slang/ An attack that penetrates your system where no attack
has ever gone before.
Deprecated Usage: IDOCs SHOULD NOT use this term; it is a joke for
Trekkies. (See: Deprecated Usage under "Green Book".)
(I) /adjective/ Refers to a cryptographic key or other parameter
that is relatively long-lived. (Compare: ephemeral.)
(I) Methods of hiding the existence of a message or other data.
This is different than cryptography, which hides the meaning of a
message but does not hide the message itself. Examples: For
classic, physical methods, see [Kahn]; for modern, digital
methods, see [John]. (See: cryptology. Compare: concealment
system, digital watermarking.)
$ storage channel
(I) See: covert storage channel.
$ storage key
(I) A cryptographic key used by a device for protecting
information that is being maintained in the device, as opposed to
protecting information that is being transmitted between devices.
(See: cryptographic token, token copy. Compare: traffic key.)
$ stream cipher
(I) An encryption algorithm that breaks plain text into a stream
of successive elements (usually, bits) and encrypts the n-th
plaintext element with the n-th element of a parallel key stream,
thus converting the plaintext stream into a ciphertext stream.
[Schn] (See: block cipher.)
$ stream integrity service
(I) A data integrity service that preserves integrity for a
sequence of data packets, including both (a) bit-by-bit datagram
integrity of each individual packet in the set and (b) packet-by-
packet sequential integrity of the set as a whole. (See: data
integrity. Compare: datagram integrity service.)
Tutorial: Some internetwork applications need only datagram
integrity, but others require that an entire stream of packets be
protected against insertion, reordering, deletion, and delay:
- "Insertion": The destination receives an additional packet that
was not sent by the source.
- "Reordering": The destination receives packets in a different
order than that in which they were sent by the source.
- "Deletion": A packet sent by the source is not ever delivered
to the intended destination.
- "Delay": A packet is detained for some period of time at a
relay, thus hampering and postponing the packet's normal timely
delivery from source to destination.
1. (I) /cryptography/ A cryptographic mechanism's level of
resistance to attacks [R3766]. (See: entropy, strong, work
2. (N) /Common Criteria/ "Strength of function" is a
"qualification of a TOE security function expressing the minimum
efforts assumed necessary to defeat its expected security behavior
by directly attacking its underlying security mechanisms": (See:
- Basic: "A level of the TOE strength of function where analysis
shows that the function provides adequate protection against
casual breach of TOE security by attackers possessing a low
- Medium: "... against straightforward or intentional breach ...
by attackers possessing a moderate attack potential."
- High: "... against deliberately planned or organized breach ...
by attackers possessing a high attack potential."
1. (I) /cryptography/ Used to describe a cryptographic algorithm
that would require a large amount of computational power to defeat
it. (See: strength, work factor, weak key.)
2. (I) /COMPUSEC/ Used to describe a security mechanism that would
be difficult to defeat. (See: strength, work factor.)
$ strong authentication
1. (I) An authentication process that uses a cryptographic
security mechanism -- particularly public-key certificates -- to
verify the identity claimed for an entity. (Compare: simple
2. (O) "Authentication by means of cryptographically derived
1a. (I) A process in a computer system that represents a principal
and that executes with the privileges that have been granted to
that principal. (Compare: principal, user.)
1b. (I) /formal model/ A system entity that causes information to
flow among objects or changes the system state; technically, a
process-domain pair. A subject may itself be an object relative to
some other subject; thus, the set of subjects in a system is a
subset of the set of objects. (See: Bell-LaPadula model, object.)
2. (I) /digital certificate/ The name (of a system entity) that is
bound to the data items in a digital certificate; e.g., a DN that
is bound to a key in a public-key certificate. (See: X.509.)
$ subject CA
(D) The CA that is the subject of a cross-certificate issued by
another CA. [X509] (See: cross-certification.)
Deprecated Term: IDOCs SHOULD NOT use this term because it is not
widely known and could be misunderstood. Instead, say "the CA that
is the subject of the cross-certificate".
(N) An OSI term for a system of packet relays and connecting links
that implement OSIRM layer 2 or 3 to provide a communication
service that interconnects attached end systems. Usually, the
relays are all of the same type (e.g., X.25 packet switches, or
interface units in an IEEE 802.3 LAN). (See: gateway, internet,
$ subordinate CA (SCA)
1. (I) A CA whose public-key certificate is issued by another
(superior) CA. (See: certification hierarchy. Compare: cross-
2. (O) /MISSI/ The fourth-highest (i.e., bottom) level of a MISSI
certification hierarchy; a MISSI CA whose public-key certificate
is signed by a MISSI CA rather than by a MISSI PCA. A MISSI SCA is
the administrative authority for a subunit of an organization,
established when it is desirable to organizationally distribute or
decentralize the CA service. The term refers both to that
authoritative office or role, and to the person who fills that
office. A MISSI SCA registers end users and issues their
certificates and may also register ORAs, but may not register
other CAs. An SCA periodically issues a CRL.
$ subordinate DN
(I) An X.500 DN is subordinate to another X.500 DN if it begins
with a set of attributes that is the same as the entire second DN
except for the terminal attribute of the second DN (which is
usually the name of a CA). For example, the DN <C=FooLand, O=Gov,
OU=Treasurer, CN=DukePinchpenny> is subordinate to the DN
<C=FooLand, O=Gov, CN=KingFooCA>.
(I) /PKI/ A user that is registered in a PKI and, therefore, can
be named in the "subject" field of a certificate issued by a CA in
that PKI. (See: registration, user.)
Usage: This term is needed to distinguish registered users from
two other kinds of PKI users:
- Users that access the PKI but are not identified to it: For
example, a relying party may access a PKI repository to obtain
the certificate of some other party. (See: access.)
- Users that do not access the PKI: For example, a relying party
(see: certificate user) may use a digital certificate that was
obtained from a database that is not part of the PKI that
issued the certificate.
1. (I) /cryptography/ A method of encryption in which elements of
the plain text retain their sequential position but are replaced
by elements of cipher text. (Compare: transposition.)
2. (I) /threat action/ See: secondary definition under
(I) A collection of related system components that together
perform a system function or deliver a system service.
(I) An encryption operation for which the plaintext input to be
transformed is the ciphertext output of a previous encryption
operation. (Compare: hybrid encryption.)
(I) /UNIX/ Synonym for "root".
(I) The ability of a system to remain in operation or existence
despite adverse conditions, including natural occurrences,
accidental actions, and attacks. (Compare: availability,
(I) An encryption protocol for IP that provides confidentiality,
integrity, and authentication and can be used for both end-to-end
and intermediate-hop security. [Ioan] (Compare: IPsec.)
Tutorial: The swIPe protocol is an IP predecessor that is
concerned only with encryption mechanisms; policy and key
management are handled outside the protocol.
(N) /encryption/ A list of individual letters, combinations of
letters, or syllables, with their equivalent code groups, used for
spelling out proper names or other unusual words that are not
present in the basic vocabulary (i.e., are not in the codebook) of
a code used for encryption.
$ symmetric cryptography
(I) A branch of cryptography in which the algorithms use the same
key for both of two counterpart cryptographic operations (e.g.,
encryption and decryption). (See: asymmetric cryptography.
Compare: secret-key cryptography.)
Tutorial: Symmetric cryptography has been used for thousands of
years [Kahn]. A modern example is AES.
Symmetric cryptography has a disadvantage compared to asymmetric
cryptography with regard to key distribution. For example, when
Alice wants to ensure confidentiality for data she sends to Bob,
she encrypts the data with a key, and Bob uses the same key to
decrypt. However, keeping the shared key secret entails both cost
and risk when the key is distributed to both Alice and Bob. (See:
key distribution, key management.)
$ symmetric key
(I) A cryptographic key that is used in a symmetric cryptographic
algorithm. (See: symmetric cryptography.)
$ SYN flood
(I) A denial-of-service attack that sends a large number of TCP
SYN (synchronize) packets to a host with the intent of disrupting
the operation of that host. (See: blind attack, flooding.)
Tutorial: This attack seeks to exploit a vulnerability in the TCP
specification or in a TCP implementation. Normally, two hosts use
a three-way exchange of packets to establish a TCP connection: (a)
host 1 requests a connection by sending a SYN packet to host 2;
(b) host 2 replies by sending a SYN-ACK (acknowledgement) packet
to host 1; and (c) host 1 completes the connection by sending an
ACK packet to host 2. To attack host 2, host 1 can send a series
of TCP SYNs, each with a different phony source address. ([R2827]
discusses how to use packet filtering to prevent such attacks from
being launched from behind an Internet service provider's
aggregation point.) Host 2 treats each SYN as a request from a
separate host, replies to each with a SYN-ACK, and waits to
receive the matching ACKs. (The attacker can use random or
unreachable sources addresses in the SYN packets, or can use
source addresses that belong to third parties, that then become
For each SYN-ACK that is sent, the TCP process in host 2 needs
some memory space to store state information while waiting for the
matching ACK to be returned. If the matching ACK never arrives at
host 2, a timer associated with the pending SYN-ACK will
eventually expire and release the space. But if host 1 (or a
cooperating group of hosts) can rapidly send many SYNs to host 2,
host 2 will need to store state information for many pending SYN-
ACKs and may run out of space. This can prevent host 2 from
responding to legitimate connection requests from other hosts or
even, if there are flaws in host 2's TCP implementation, crash
when the available space is exhausted.
(I) Any technique by which a receiving (decrypting) cryptographic
process attains an internal state that matches the transmitting
(encrypting) process, i.e., has the appropriate keying material to
process the cipher text and is correctly initialized to do so.
(I) Synonym for "information system".
Usage: This is a generic definition, and is the one with which the
term is used in this Glossary. However, IDOCs that use the term,
especially IDOCs that are protocol specifications, SHOULD state a
more specific definition. Also, IDOCs that specify security
features, services, and assurances need to define which system
components and system resources are inside the applicable security
perimeter and which are outside. (See: security architecture.)
$ system architecture
(N) The structure of system components, their relationships, and
the principles and guidelines governing their design and evolution
over time. [DoD10] (Compare: security architecture.)
$ system component
1. (I) A collection of system resources that (a) forms a physical
or logical part of the system, (b) has specified functions and
interfaces, and (c) is treated (e.g., by policies or
specifications) as existing independently of other parts of the
system. (See: subsystem.)
2. (O) /ITSEC/ An identifiable and self-contained part of a TOE.
Usage: Component is a relative term because components may be
nested; i.e., one component of a system may be a part of another
component of that system.
Tutorial: Components can be characterized as follows:
- A "physical component" has mass and takes up space.
- A "logical component" is an abstraction used to manage and
coordinate aspects of the physical environment, and typically
represents a set of states or capabilities of the system.
$ system entity
(I) An active part of a system -- a person, a set of persons
(e.g., some kind of organization), an automated process, or a set
of processes (see: subsystem) -- that has a specific set of
capabilities. (Compare: subject, user.)
$ system high
(I) The highest security level at which a system operates, or is
capable of operating, at a particular time or in a particular
environment. (See: system-high security mode.)
$ system-high security mode
(I) A mode of system operation wherein all users having access to
the system possess all necessary authorizations (both security
clearance and formal access approval) for all data handled by the
system, but some users might not have need-to-know for all the
data. (See: /system operation/ under "mode", formal access
approval, protection level, security clearance.)
Usage: Usually abbreviated as "system-high mode". This mode was
defined in U.S. DoD policy that applied to system accreditation,
but the term is widely used outside the Government.
$ system integrity
1. (I) An attribute or quality "that a system has when it can
perform its intended function in a unimpaired manner, free from
deliberate or inadvertent unauthorized manipulation." [C4009,
NCS04] (See: recovery, system integrity service.)
2. (D) "Quality of an [information system] reflecting the logical
correctness and reliability of the operating system; the logical
completeness of the hardware and software implementing the
protection mechanisms; and the consistency of the data structures
and occurrence of the stored data." [from an earlier version of
Deprecated Definition: IDOCs SHOULD NOT use definition 2 because
it mixes several concepts in a potentially misleading way.
Instead, IDOCs should use the term with definition 1 and,
depending on what is meant, couple the term with additional, more
specifically descriptive and informative terms, such as
"correctness", "reliability", and "data integrity".
$ system integrity service
(I) A security service that protects system resources in a
verifiable manner against unauthorized or accidental change, loss,
or destruction. (See: system integrity.)
$ system low
(I) The lowest security level supported by a system at a
particular time or in a particular environment. (Compare: system
$ system resource
(I) Data contained in an information system; or a service provided
by a system; or a system capacity, such as processing power or
communication bandwidth; or an item of system equipment (i.e.,
hardware, firmware, software, or documentation); or a facility
that houses system operations and equipment. (See: system
$ system security officer (SSO)
(I) A person responsible for enforcement or administration of the
security policy that applies to a system. (Compare: manager,
$ system user
(I) A system entity that consumes a product or service provided by
the system, or that accesses and employs system resources to
produce a product or service of the system. (See: access, [R2504].
Compare: authorized user, manager, operator, principal, privileged
user, subject, subscriber, system entity, unauthorized user.)
Usage: IDOCs that use this term SHOULD state a definition for it
because the term is used in many ways and could easily be
- This term usually refers to an entity that has been authorized
to access the system, but the term sometimes is used without
regard for whether access is authorized.
- This term usually refers to a living human being acting either
personally or in an organizational role. However, the term also
may refer to an automated process in the form of hardware,
software, or firmware; to a set of persons; or to a set of
- IDOCs SHOULD NOT use the term to refer to a mixed set
containing both persons and processes. This exclusion is
intended to prevent situations that might cause a security
policy to be interpreted in two different and conflicting ways.
A system user can be characterized as direct or indirect:
- "Passive user": A system entity that is (a) outside the
system's security perimeter *and* (b) can receive output from
the system but cannot provide input or otherwise interact with
- "Active user": A system entity that is (a) inside the system's
security perimeter *or* (b) can provide input or otherwise
interact with the system.
(I) See: Terminal Access Controller (TAC) Access Control System.
(I) A TCP-based protocol that improves on TACACS by separating the
functions of authentication, authorization, and accounting and by
encrypting all traffic between the network access server and
authentication server. TACACS+ is extensible to allow any
authentication mechanism to be used with TACACS+ clients.
(I) Make an unauthorized modification in a system that alters the
system's functioning in a way that degrades the security services
that the system was intended to provide. (See: QUADRANT. Compare:
secondary definitions under "corruption" and "misuse".)
(I) A characteristic of a system component that provides evidence
that an attack has been attempted on that component or system.
Usage: Usually involves physical evidence. (See: tamper.)
(I) A characteristic of a system component that provides passive
protection against an attack. (See: tamper.)
Usage: Usually involves physical means of protection.
(I) /threat action/ See: secondary definitions under "corruption"
$ target of evaluation (TOE)
(N) /Common Criteria/ An information technology product or system
that is the subject of a security evaluation, together with the
product's associated administrator and user documentation.
(Compare: protection profile.)
Tutorial: The security characteristics of the target of evaluation
(TOE) are described in specific terms by a corresponding security
target, or in more general terms by a protection profile. In
Common Criteria philosophy, it is important that a TOE be
evaluated against the specific set of criteria expressed in the
target. This evaluation consists of rigorous analysis and testing
performed by an accredited, independent laboratory. The scope of a
TOE evaluation is set by the EAL and other requirements specified
in the target. Part of this process is an evaluation of the target
itself, to ensure that it is correct, complete, and internally
consistent and can be used as the baseline for the TOE evaluation.
(N) See: trusted computing base.
$ TCC field
(I) See: Transmission Control Code field.
(N) See: Trusted Computing Group.
(I) See: Transmission Control Protocol.
(I) Synonym for "Internet Protocol Suite".
(N) See: Trusted Computer System Evaluation Criteria. (Compare:
(I) See: Triple Data Encryption Algorithm.
$ teardrop attack
(D) /slang/ A denial-of-service attack that sends improperly
formed IP packet fragments with the intent of causing the
destination system to fail.
Deprecated Term: IDOCs that use this term SHOULD state a
definition for it because the term is often used imprecisely and
could easily be misunderstood. (See: Deprecated Usage under "Green
$ technical non-repudiation
(I) See: (secondary definition under) non-repudiation.
$ technical security
(I) Security mechanisms and procedures that are implemented in and
executed by computer hardware, firmware, or software to provide
automated protection for a system. (See: security architecture.
Compare: administrative security.)
$ Telecommunications Security Word System (TSEC)
(O) /U.S. Government/ A terminology for designating
telecommunication security equipment. (Compare: TCSEC.)
Tutorial: A TSEC designator has the following parts:
- Prefix "TSEC/" for items and systems, or suffix "/TSEC" for
assemblies. (Often omitted when the context is clear.)
- First letter, for function: "C" COMSEC equipment system, "G"
general purpose, "K" cryptographic, "H" crypto-ancillary, "M"
manufacturing, "N" noncryptographic, "S" special purpose.
- Second letter, for type or purpose: "G" key generation, "I"
data transmission, "L" literal conversion, "N" signal
conversion, "O" multipurpose, "P" materials production, "S"
special purpose, "T" testing or checking, "U" television, "W"
teletypewriter, "X" facsimile, "Y" speech.
- Optional third letter, used only in designations of assemblies,
for type or purpose: "A" advancing, "B" base or cabinet, "C"
combining, "D" drawer or panel, "E" strip or chassis, "F" frame
or rack, "G" key generator, "H" keyboard, "I" translator or
reader, "J" speech processing, "K" keying or permuting, "L"
repeater, "M" memory or storage, "O" observation, "P" power
supply or converter, "R" receiver, "S" synchronizing, "T"
transmitter, "U" printer, "V" removable COMSEC component, "W"
logic programmer/programming, "X" special purpose.
- Model number, usually two or three digits, assigned
sequentially within each letter combination (e.g., KG-34, KG-
- Optional suffix letter, used to designate a version. First
version has no letter, next version has "A" (e.g., KG-84, KG-
(I) A TCP-based, Application-Layer, Internet Standard protocol
(RFC 854) for remote login from one host to another.
1. (N) Short name for technology and methods for protecting
against data compromise due to electromagnetic emanations from
electrical and electronic equipment. [Army, Russ] (See:
inspectable space, soft TEMPEST, TEMPEST zone. Compare: QUADRANT)
2. (O) /U.S. Government/ "Short name referring to investigation,
study, and control of compromising emanations from IS equipment."
Deprecated Usage: IDOCs SHOULD NOT use this term as a synonym for
"electromagnetic emanations security"; instead, use EMSEC. Also,
the term is NOT an acronym for Transient Electromagnetic Pulse
Tutorial: The U.S. Federal Government issues security policies
that (a) state specifications and standards for techniques to
reduce the strength of emanations from systems and reduce the
ability of unauthorized parties to receive and make use of
emanations and (b) state rules for applying those techniques.
Other nations presumably do the same.
$ TEMPEST zone
(O) "Designated area [i.e., a physical volume] within a facility
where equipment with appropriate TEMPEST characteristics ... may
be operated." [C4009] (See: emanation security, TEMPEST. Compare:
control zone, inspectable space.)
Tutorial: The strength of an electromagnetic signal decreases in
proportion to the square of the distance between the source and
the receiver. Therefore, EMSEC for electromagnetic signals can be
achieved by a combination of (a) reducing the strength of
emanations to a defined level and (b) establishing around that
equipment an appropriately sized physical buffer zone from which
unauthorized entities are excluded. By making the zone large
enough, it is possible to limit the signal strength available to
entities outside the zone to a level lower than can be received
and read with known, state-of-the-art methods. Typically, the need
for and size of a TEMPEST zone established by a security policy
depends not only on the measured level of signal emitted by
equipment, but also on the perceived threat level in the
$ Terminal Access Controller (TAC) Access Control System (TACACS)
(I) A UDP-based authentication and access control protocol [R1492]
in which a network access server receives an identifier and
password from a remote terminal and passes them to a separate
authentication server for verification. (See: TACACS+.)
Tutorial: TACACS can provide service not only for network access
servers but also routers and other networked computing devices via
one or more centralized authentication servers. TACACS was
originally developed for ARPANET and has evolved for use in
(I) See: The Exponential Encryption System.
$ The Exponential Encryption System (TESS)
(I) A system of separate but cooperating cryptographic mechanisms
and functions for the secure authenticated exchange of
cryptographic keys, the generation of digital signatures, and the
distribution of public keys. TESS uses asymmetric cryptography,
based on discrete exponentiation, and a structure of self-
certified public keys. [R1824]
(I) /threat action/ See: secondary definitions under
"interception" and "misappropriation".
1a. (I) A potential for violation of security, which exists when
there is an entity, circumstance, capability, action, or event
that could cause harm. (See: dangling threat, INFOCON level,
threat action, threat agent, threat consequence. Compare: attack,
1b. (N) Any circumstance or event with the potential to adversely
affect a system through unauthorized access, destruction,
disclosure, or modification of data, or denial of service. [C4009]
(See: sensitive information.)
Usage: (a) Frequently misused with the meaning of either "threat
action" or "vulnerability". (b) In some contexts, "threat" is used
more narrowly to refer only to intelligent threats; for example,
see definition 2 below. (c) In some contexts, "threat" is used
more broadly to cover both definition 1 and other concepts, such
as in definition 3 below.
Tutorial: A threat is a possible danger that might exploit a
vulnerability. Thus, a threat may be intentional or not:
- "Intentional threat": A possibility of an attack by an
intelligent entity (e.g., an individual cracker or a criminal
- "Accidental threat": A possibility of human error or omission,
unintended equipment malfunction, or natural disaster (e.g.,
fire, flood, earthquake, windstorm, and other causes listed in
The Common Criteria characterizes a threat in terms of (a) a
threat agent, (b) a presumed method of attack, (c) any
vulnerabilities that are the foundation for the attack, and (d)
the system resource that is attacked. That characterization agrees
with the definitions in this Glossary (see: diagram under
2. (O) The technical and operational ability of a hostile entity
to detect, exploit, or subvert a friendly system and the
demonstrated, presumed, or inferred intent of that entity to
conduct such activity.
Tutorial: To be likely to launch an attack, an adversary must have
(a) a motive to attack, (b) a method or technical ability to make
the attack, and (c) an opportunity to appropriately access the
3. (D) "An indication of an impending undesirable event." [Park]
Deprecated Definition: IDOCs SHOULD NOT use this term with
definition 3 because the definition is ambiguous; the definition
was intended to include the following three meanings:
- "Potential threat": A possible security violation; i.e., the
same as definition 1.
- "Active threat": An expression of intent to violate security.
(Context usually distinguishes this meaning from the previous
- "Accomplished threat" or "actualized threat": That is, a threat
action. Deprecated Usage: IDOCs SHOULD NOT use the term
"threat" with this meaning; instead, use "threat action".
$ threat action
(I) A realization of a threat, i.e., an occurrence in which system
security is assaulted as the result of either an accidental event
or an intentional act. (See: attack, threat, threat consequence.)
Tutorial: A complete security architecture deals with both
intentional acts (i.e., attacks) and accidental events [FP031].
(See: various kinds of threat actions defined under the four kinds
of "threat consequence".)
$ threat agent
(I) A system entity that performs a threat action, or an event
that results in a threat action.
$ threat analysis
(I) An analysis of the threat actions that might affect a system,
primarily emphasizing their probability of occurrence but also
considering their resulting threat consequences. Example: RFC
3833. (Compare: risk analysis.)
$ threat consequence
(I) A security violation that results from a threat action.
Tutorial: The four basic types of threat consequence are
"unauthorized disclosure", "deception", "disruption", and
"usurpation". (See main Glossary entries of each of these four
terms for lists of the types of threat actions that can result in
1. (I) A pattern of curves formed by the ridges on the tip of a
thumb. (See: biometric authentication, fingerprint.)
2. (D) Synonym for some type of "hash result". (See: biometric
authentication. Compare: fingerprint.)
Deprecated Usage: IDOCs SHOULD NOT use this term with definition 2
because that meaning mixes concepts in a potentially misleading
(I) Synonym for "capability token".
Tutorial: A ticket is usually granted by a centralized access
control server (ticket-granting agent) to authorize access to a
system resource for a limited time. Tickets can be implemented
with either symmetric cryptography (see: Kerberos) or asymmetric
cryptography (see: attribute certificate).
$ tiger team
(O) A group of evaluators employed by a system's managers to
perform penetration tests on the system.
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".)
$ time stamp
1. (I) /noun/ With respect to a data object, a label or marking in
which is recorded the time (time of day or other instant of
elapsed time) at which the label or marking was affixed to the
data object. (See: Time-Stamp Protocol.)
2. (O) /noun/ "With respect to a recorded network event, a data
field in which is recorded the time (time of day or other instant
of elapsed time) at which the event took place." [A1523]
Tutorial: A time stamp can be used as evidence to prove that a
data object existed (or that an event occurred) at or before a
particular time. For example, a time stamp might be used to prove
that a digital signature based on a private key was created while
the corresponding public-key certificate was valid, i.e., before
the certificate either expired or was revoked. Establishing this
proof would enable the certificate to be used after its expiration
or revocation, to verify a signature that was created earlier.
This kind of proof is required as part of implementing PKI
services, such as non-repudiation service, and long-term security
services, such as audit.
$ Time-Stamp Protocol
(I) An Internet protocol (RFC 3161) that specifies how a client
requests and receives a time stamp from a server for a data object
held by the client.
Tutorial: The protocol describes the format of (a) a request sent
to a time-stamp authority and (b) the response that is returned
containing a time stamp. The authority creates the stamp by
concatenating (a) a hash value of the input data object with (b) a
UTC time value and other parameters (policy OID, serial number,
indication of time accuracy, nonce, DN of the authority, and
various extensions), and then signing that dataset with the
authority's private key as specified in CMS. Such an authority
typically would operate as a trusted third-party service, but
other operational models might be used.
$ timing channel
(I) See: covert timing channel.
(I) A mnemonic referring to an Internet protocol (RFC 2930) for
establishing a shared secret key between a DNS resolver and a DNS
name server. (See: TSIG.)
(I) See: Transport Layer Security.
(N) See: Transport Layer Security Protocol.
(N) See: target of evaluation.
1. (I) /cryptography/ See: cryptographic token. (Compare: dongle.)
2. (I) /access control/ An object that is used to control access
and is passed between cooperating entities in a protocol that
synchronizes use of a shared resource. Usually, the entity that
currently holds the token has exclusive access to the resource.
(See: capability token.)
Usage: This term is heavily overloaded in the computing
literature; therefore, IDOCs SHOULD NOT use this term with any
definition other than 1 or 2.
3a. (D) /authentication/ A data object or a physical device used
to verify an identity in an authentication process.
3b. (D) /U.S. Government/ Something that the claimant in an
authentication process (i.e., the entity that claims an identity)
possesses and controls, and uses to prove the claim during the
verification step of the process. [SP63]
Deprecated usage: IDOCs SHOULD NOT use this term with definitions
3a and 3b; instead, use more specifically descriptive and
informative terms such as "authentication information" or
"cryptographic token", depending on what is meant.
NIST defines four types of claimant tokens for electronic
authentication in an information system [SP63]. IDOCs SHOULD NOT
use these four NIST terms; they mix concepts in potentially
confusing ways and duplicate the meaning of better-established
terms. These four terms can be avoided by using more specifically
descriptive terms as follows:
- NIST "hard token": A hardware device that contains a protected
cryptographic key. (This is a type of "cryptographic token",
and the key is a type of "authentication information".)
- NIST "one-time password device token": A personal hardware
device that generates one-time passwords. (One-time passwords
are typically generated cryptographically. Therefore, this is a
type of "cryptographic token", and the key is a type of
- NIST "soft token": A cryptographic key that typically is stored
on disk or some other magnetic media. (The key is a type of
"authentication information"; "authentication key" would be a
- NIST "password token": A secret data value that the claimant
memorizes. (This is a "password" that is being used as
$ token backup
(I) A token management operation that stores sufficient
information in a database (e.g., in a CAW) to recreate or restore
a security token (e.g., a smart card) if it is lost or damaged.
$ token copy
(I) A token management operation that copies all the personality
information from one security token to another. However, unlike in
a token restore operation, the second token is initialized with
its own, different local security values such as PINs and storage
$ token management
(I) The process that includes initializing security tokens (e.g.,
"smart card"), loading data into the tokens, and controlling the
tokens during their lifecycle. May include performing key
management and certificate management functions; generating and
installing PINs; loading user personality data; performing card
backup, card copy, and card restore operations; and updating