L <- 4. Definitions -> N

M English

$ MAC

(N) See: mandatory access control, Message Authentication Code.

Deprecated Usage: IDOCs that use this term SHOULD state a definition for it because this abbreviation is ambiguous.

$ magnetic remanence

(N) Magnetic representation of residual information remaining on a magnetic medium after the medium has been cleared. [NCS25] (See: clear, degauss, purge.)

$ main mode

(I) See: /IKE/ under "mode".

$ maintenance hook

(N) "Special instructions (trapdoors) in software allowing easy maintenance and additional feature development. Since maintenance hooks frequently allow entry into the code without the usual checks, they are a serious security risk if they are not removed prior to live implementation." [C4009] (See: back door.)

$ malicious logic

(I) Hardware, firmware, or software that is intentionally included or inserted in a system for a harmful purpose. (See: logic bomb, Trojan horse, spyware, virus, worm. Compare: secondary definitions under "corruption", "incapacitation", "masquerade", and "misuse".)

$ malware

(D) A contraction of "malicious software". (See: malicious logic.)

Deprecated Term: IDOCs SHOULD NOT use this term; it is not listed in most dictionaries and could confuse international readers.

$ MAN

(I) metropolitan area network.

$ man-in-the-middle attack

(I) A form of active wiretapping attack in which the attacker intercepts and selectively modifies communicated data to masquerade as one or more of the entities involved in a communication association. (See: hijack attack, piggyback attack.)

Tutorial: For example, suppose Alice and Bob try to establish a session key by using the Diffie-Hellman-Merkle algorithm without data origin authentication service. A "man in the middle" could (a) block direct communication between Alice and Bob and then (b) masquerade as Alice sending data to Bob, (c) masquerade as Bob sending data to Alice, (d) establish separate session keys with each of them, and (e) function as a clandestine proxy server between them to capture or modify sensitive information that Alice and Bob think they are sending only to each other.

$ manager

(I) A person who controls the service configuration of a system or the functional privileges of operators and other users. (See: administrative security. Compare: operator, SSO, user.)

$ mandatory access control

1. (I) An access control service that enforces a security policy based on comparing (a) security labels, which indicate how sensitive or critical system resources are, with (b) security clearances, which indicate that system entities are eligible to access certain resources. (See: discretionary access control, MAC, rule-based security policy.)

Derivation: This kind of access control is called "mandatory" because an entity that has clearance to access a resource is not permitted, just by its own volition, to enable another entity to access that resource.

2. (O) "A means of restricting access to objects based on the sensitivity (as represented by a label) of the information contained in the objects and the formal authorization (i.e., clearance) of subjects to access information of such sensitivity." [DoD1]

$ manipulation detection code

(D) Synonym for "checksum".

Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for "checksum"; the word "manipulation" implies protection against active attacks, which an ordinary checksum might not provide. Instead, if such protection is intended, use "protected checksum" or some particular type thereof, depending on which is meant. If such protection is not intended, use "error detection code" or some specific type of checksum that is not protected.

$ marking

See: time stamp, security marking.

$ MARS

(O) A symmetric, 128-bit block cipher with variable key length (128 to 448 bits), developed by IBM as a candidate for the AES.

$ Martian

(D) /slang/ A packet that arrives unexpectedly at the wrong address or on the wrong network because of incorrect routing or because it has a non-registered or ill-formed IP address. [R1208]

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. (See: Deprecated Usage under "Green Book".)

$ masquerade

(I) A type of threat action whereby an unauthorized entity gains access to a system or performs a malicious act by illegitimately posing as an authorized entity. (See: deception.)

Usage: This type of threat action includes the following subtypes:

• "Spoof": Attempt by an unauthorized entity to gain access to a system by posing as an authorized user.
• "Malicious logic": In context of masquerade, any hardware, firmware, or software (e.g., Trojan horse) that appears to perform a useful or desirable function, but actually gains unauthorized access to system resources or tricks a user into executing other malicious logic. (See: corruption, incapacitation, main entry for "malicious logic", misuse.)

$ MCA

(O) See: merchant certification authority.

$ MD2

(N) A cryptographic hash [R1319] that produces a 128-bit hash result, was designed by Ron Rivest, and is similar to MD4 and MD5 but slower.

Derivation: Apparently, an abbreviation of "message digest", but that term is deprecated by this Glossary.

$ MD4

(N) A cryptographic hash [R1320] that produces a 128-bit hash result and was designed by Ron Rivest. (See: Derivation under "MD2", SHA-1.)

$ MD5

(N) A cryptographic hash [R1321] that produces a 128-bit hash result and was designed by Ron Rivest to be an improved version of MD4. (See: Derivation under "MD2".)

$ merchant

(O) /SET/ "A seller of goods, services, and/or other information who accepts payment for these items electronically." [SET2] A merchant may also provide electronic selling services and/or electronic delivery of items for sale. With SET, the merchant can offer its cardholders secure electronic interactions, but a merchant that accepts payment cards is required to have a relationship with an acquirer. [SET1, SET2]

$ merchant certificate

(O) /SET/ A public-key certificate issued to a merchant. Sometimes used to refer to a pair of such certificates where one is for digital signature use and the other is for encryption.

$ merchant certification authority (MCA)

(O) /SET/ A CA that issues digital certificates to merchants and is operated on behalf of a payment card brand, an acquirer, or another party according to brand rules. Acquirers verify and approve requests for merchant certificates prior to issuance by the MCA. An MCA does not issue a CRL, but does distribute CRLs issued by root CAs, brand CAs, geopolitical CAs, and payment gateway CAs. [SET2]

$ mesh PKI

(I) A non-hierarchical PKI architecture in which there are several trusted CAs rather than a single root. Each certificate user bases path validations on the public key of one of the trusted CAs, usually the one that issued that user's own public-key certificate. Rather than having superior-to-subordinate relationships between CAs, the relationships are peer-to-peer, and CAs issue cross-certificates to each other. (Compare: hierarchical PKI, trust-file PKI.)

$ Message Authentication Code (MAC), message authentication code

1. (N) /capitalized/ A specific ANSI standard for a checksum that is computed with a keyed hash that is based on DES. [A9009] Usage: a.k.a. Data Authentication Code, which is a U.S. Government standard. [FP113] (See: MAC.)

2. (D) /not capitalized/ Synonym for "error detection code".

Deprecated Term: IDOCs SHOULD NOT use the uncapitalized form "message authentication code". Instead, use "checksum", "error detection code", "hash", "keyed hash", "Message Authentication Code", or "protected checksum", depending on what is meant. (See: authentication code.)

The uncapitalized form mixes concepts in a potentially misleading way. The word "message" is misleading because it implies that the mechanism is particularly suitable for or limited to electronic mail (see: Message Handling Systems). The word "authentication" is misleading because the mechanism primarily serves a data integrity function rather than an authentication function. The word "code" is misleading because it implies that either encoding or encryption is involved or that the term refers to computer software.

$ message digest

(D) Synonym for "hash result". (See: cryptographic hash.)

Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for "hash result"; this term unnecessarily duplicates the meaning of the other, more general term and mixes concepts in a potentially misleading way. The word "message" is misleading because it implies that the mechanism is particularly suitable for or limited to electronic mail (see: Message Handling Systems).

$ message handling system

(D) Synonym for the Internet electronic mail system.

Deprecated Term: IDOCs SHOULD NOT use this term, because it could be confused with Message Handling System. Instead, use "Internet electronic mail" or some other, more specific term.

$ Message Handling System

(O) An ITU-T system concept that encompasses the notion of electronic mail but defines more comprehensive OSI systems and services that enable users to exchange messages on a store-and- forward basis. (The ISO equivalent is "Message Oriented Text Interchange System".) (See: X.400.)

$ message indicator

1. (D) /cryptographic function/ Synonym for "initialization value". (Compare: indicator.)

2. (D) "Sequence of bits transmitted over a communications system for synchronizing cryptographic equipment." [C4009]

Deprecated Term: IDOCs SHOULD NOT use this term as a synonym for "initialization value"; the term mixes concepts in a potentially misleading way. The word "message" is misleading because it suggests that the mechanism is specific to electronic mail. (See: Message Handling System.)

$ message integrity check
$ message integrity code (MIC)

(D) Synonyms for some form of "checksum".

Deprecated Term: IDOCs SHOULD NOT use these terms for any form of checksum. Instead, use "checksum", "error detection code", "hash", "keyed hash", "Message Authentication Code", or "protected checksum", depending on what is meant.

These two terms mix concepts in potentially misleading ways. The word "message" is misleading because it suggests that the mechanism is particularly suitable for or limited to electronic mail. The word "integrity" is misleading because the checksum may be used to perform a data origin authentication function rather than an integrity function. The word "code" is misleading because it suggests either that encoding or encryption is involved or that the term refers to computer software.

$ Message Security Protocol (MSP)

(N) A secure message handling protocol [SDNS7] for use with X.400 and Internet mail protocols. Developed by NSA's SDNS program and used in the U.S. DoD's Defense Message System.

$ meta-data

(I) Descriptive information about a data object; i.e., data about data, or data labels that describe other data. (See: security label. Compare: metadata)

Tutorial: Meta-data can serve various management purposes:

• System management: File name, type, size, creation date.
• Application management: Document title, version, author.
• Usage management: Data categories, keywords, classifications.

Meta-data can be associated with a data object in two basic ways:

• Explicitly: Be part of the data object (e.g., a header field of a data file or packet) or be linked to the object.
• Implicitly: Be associated with the data object because of some other, explicit attribute of the object.

$ metadata, Metadata(trademark), METADATA(trademark)

(D) Proprietary variants of "meta-data". (See: SPAM(trademark).)

Deprecated Usage: IDOCs SHOULD NOT use these unhypenated forms; IDOCs SHOULD use only the uncapitalized, hyphenated "meta-data". The terms "Metadata" and "METADATA" are claimed as registered trademarks (numbers 1,409,260 and 2,185,504) owned by The Metadata Company, originally known as Metadata Information Partners, a company founded by Jack Myers. The status of "metadata" is unclear.

$ MHS

(N) See: message handling system.

$ MIC

(D) See: message integrity code.

$ MIME

(I) See: Multipurpose Internet Mail Extensions.

$ MIME Object Security Services (MOSS)

(I) An Internet protocol [R1848] that applies end-to-end encryption and digital signature to MIME message content, using symmetric cryptography for encryption and asymmetric cryptography for key distribution and signature. MOSS is based on features and specifications of PEM. (See: S/MIME.)

$ Minimum Interoperability Specification for PKI Components

(MISPC) (N) A technical description to provide a basis for interoperation between PKI components from different vendors; consists primarily of a profile of certificate and CRL extensions and a set of transactions for PKI operation. [SP15]

$ misappropriation

(I) A type of threat action whereby an entity assumes unauthorized logical or physical control of a system resource. (See: usurpation.)

Usage: This type of threat action includes the following subtypes:

• Theft of data: Unauthorized acquisition and use of data contained in a system.
• Theft of service: Unauthorized use of a system service.
• Theft of functionality: Unauthorized acquisition of actual hardware, firmware, or software of a system component.

$ MISPC

(N) See: Minimum Interoperability Specification for PKI Components.

$ MISSI

(O) Multilevel Information System Security Initiative, an NSA program to encourage development of interoperable, modular products for constructing secure network information systems in support of a wide variety of U.S. Government missions. (See: MSP, SP3, SP4.)

$ MISSI user

(O) /MISSI/ A system entity that is the subject of one or more MISSI X.509 public-key certificates issued under a MISSI certification hierarchy. (See: personality.)

Tutorial: MISSI users include both end users and the authorities that issue certificates. A MISSI user is usually a person but may be a machine or other automated process. Machines that are required to operate nonstop may be issued their own certificates to avoid downtime needed to exchange the FORTEZZA cards of machine operators at shift changes.

$ mission

(I) A statement of a (relatively long-term) duty or (relatively short-term) task that is assigned to an organization or system, indicates the purpose and objectives of the duty or task, and may indicate the actions to be taken to achieve it.

$ mission critical

(I) A condition of a system service or other system resource such that denial of access to, or lack of availability of, the resource would jeopardize a system user's ability to perform a primary mission function or would result in other serious consequences. (See: Critical. Compare: mission essential.)

$ mission essential

(O) /U.S. DoD/ Refers to materiel that is authorized and available to combat, combat support, combat service support, and combat readiness training forces to accomplish their assigned missions. [JP1] (Compare: mission critical.)

$ misuse

1. (I) The intentional use (by authorized users) of system resources for other than authorized purposes. Example: An authorized system administrator creates an unauthorized account for a friend. (See: misuse detection.)

2. (I) A type of threat action that causes a system component to perform a function or service that is detrimental to system security. (See: usurpation.)

Usage: This type of threat action includes the following subtypes:

• "Tampering": /misuse/ Deliberately altering a system's logic, data, or control information to cause the system to perform unauthorized functions or services. (See: corruption, main entry for "tampering".)
• "Malicious logic": /misuse/ Any hardware, firmware, or software intentionally introduced into a system to perform or control execution of an unauthorized function or service. (See: corruption, incapacitation, main entry for "malicious logic", masquerade.)
• "Violation of authorizations": Action by an entity that exceeds the entity's system privileges by executing an unauthorized function. (See: authorization.)

$ misuse detection

(I) An intrusion detection method that is based on rules that specify system events, sequences of events, or observable properties of a system that are believed to be symptomatic of security incidents. (See: IDS, misuse. Compare: anomaly detection.)

$ MLS

(I) See: multilevel secure

$ mobile code

1a. (I) Software that originates from a remote server, is transmitted across a network, and is loaded onto and executed on a local client system without explicit initiation by the client's user and, in some cases, without that user's knowledge. (Compare: active content.)

Tutorial: One form of mobile code is active content in a file that is transferred across a network.

1b. (O) /U.S. DoD/ "Software modules obtained from remote systems, transferred across a network, and then downloaded and executed on local systems without explicit installation or execution by the recipient." [JP1]

2a. (O) /U.S. DoD/ Technology that enables the creation of executable information that can be delivered to an information system and directly executed on any hardware/software architecture that has an appropriate host execution environment.

2b. (O) "Programs (e.g., script, macro, or other portable instruction) that can be shipped unchanged to a heterogeneous collection of platforms and executed with identical semantics" [SP28]. (See: active content.)

Tutorial: Mobile code might be malicious. Using techniques such as "code signing" and a "sandbox" can reduce the risks of receiving and executing mobile code.

$ mode
$ mode of operation

1. (I) /cryptographic operation/ A technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application, such as applying a block cipher to a sequence of data blocks or a data stream. (See: CBC, CCM, CMAC, CFB, CTR, ECB, OFB.)

2. (I) /system operation/ A type of security policy that states the range of classification levels of information that a system is permitted to handle and the range of clearances and authorizations of users who are permitted to access the system. (See: compartmented security mode, controlled security mode, dedicated security mode, multilevel security mode, partitioned security mode, system-high security mode. Compare: protection level.)

3. (I) /IKE/ IKE refers to its various types of ISAKMP-scripted exchanges of messages as "modes". Among these are the following:

• "Main mode": One of IKE's two phase 1 modes. (See: ISAKMP.)
• "Quick mode": IKE's only phase 2 mode. (See: ISAKMP.)

$ model

See: formal model, security model.

$ modulus

(I) The defining constant in modular arithmetic, and usually a part of the public key in asymmetric cryptography that is based on modular arithmetic. (See: Diffie-Hellman-Merkle, RSA.)

$ Mondex

(O) A smartcard-based electronic money system that incorporates cryptography and can be used to make payments via the Internet. (See: IOTP.)

$ Morris Worm

(I) A worm program that flooded the ARPANET in November 1988, causing problems for thousands of hosts. [R1135] (See: community risk, worm)

$ MOSS

(I) See: MIME Object Security Services.

$ MQV

(N) A key-agreement protocol [Mene] that was proposed by A.J. Menezes, M. Qu, and S.A. Vanstone in 1995 and is based on the Diffie-Hellman-Merkle algorithm.

$ MSP

(N) See: Message Security Protocol.

$ multicast security

See: secure multicast

$ Multics

(N) MULTiplexed Information and Computing Service, an MLS computer timesharing system designed and implemented during 1965-69 by a consortium including Massachusetts Institute of Technology, General Electric, and Bell Laboratories, and later offered commercially by Honeywell.

Tutorial: Multics was one of the first large, general-purpose, operating systems to include security as a primary goal from the inception of the design and development and was rated in TCSEC Class B2. Its many innovative hardware and software security mechanisms (e.g., protection ring) were adopted by later systems.

$ multilevel secure (MLS)

(I) Describes an information system that is trusted to contain, and maintain separation between, resources (particularly stored data) of different security levels. (Examples: BLACKER, CANEWARE, KSOS, Multics, SCOMP.)

Usage: Usually understood to mean that the system permits concurrent access by users who differ in their access authorizations, while denying users access to resources for which they lack authorization.

$ multilevel security mode

1. (N) A mode of system operation wherein (a) two or more security levels of information are allowed to be to be handled concurrently within the same system when some users having access to the system have neither a security clearance nor need-to-know for some of the data handled by the system and (b) separation of the users and the classified material on the basis, respectively, of clearance and classification level are dependent on operating system control. (See: /system operation/ under "mode", need to know, protection level, security clearance. Compare: controlled mode.)

Usage: Usually abbreviated as "multilevel mode". This term was defined in U.S. Government policy regarding system accreditation, but the term is also used outside the Government.

2. (O) A mode of system operation in which all three of the following statements are true: (a) Some authorized users do not have a security clearance for all the information handled in the system. (b) All authorized users have the proper security clearance and appropriate specific access approval for the information to which they have access. (c) All authorized users have a need-to-know only for information to which they have access. [C4009] (See: formal access approval, protection level.)

$ Multipurpose Internet Mail Extensions (MIME)

(I) An Internet protocol (RFC 2045) that enhances the basic format of Internet electronic mail messages (RFC 822) (a) to enable character sets other than U.S. ASCII to be used for textual headers and content and (b) to carry non-textual and multi-part content. (See: S/MIME.)

$ mutual suspicion

(I) The state that exists between two interacting system entities in which neither entity can trust the other to function correctly with regard to some security requirement.

L <- 4. Definitions -> N