The Rainbow Books

[Aqua Book]
Glossary of Computer Security Terms
[Version 1, 10/21/88]


AIS	Automated Information System

COMPUSEC	Computer Security

COMSEC	Communications Security

CSTVRP	Computer Security Technical Vulnerability Reporting Program

DAA	Designated Approving Authority

DAC	Discretionary Access Control

DES	Data Encryption Standard

DPL	Degausser Products List

DTLS	Descriptive Top-Level Specification

EPL	Evaluated Products List

ETL	Endorsed Tools List

FTLS	Formal Top-Level Specification

ISSO	Information System Security Officer

MAC	Mandatory Access Control

NCSC	National Computer Security Center

NTISSC 	National Telecommunications and Information Systems Security 

OPSEC	Operations Security

PPL	Preferred Products List

SAISS	Subcommittee on Automated Information Systems Security of NTISSC

SSO	System Security Officer

STS	Subcommittee on Telecommunications Security of NTISSC
TCB	Trusted Computing Base

TCSEC	DoD Trusted Computer System Evaluation Criteria


*-property (or star property)

A Bell-La Padula security model rule allowing a subject write access to an
object only if the security level of the object dominates the security level
of the subject.  Also called confinement property.


acceptance inspection
	The final inspection to determine whether or not a facility or
system meets the specified technical and performance standards.  Note: This
inspection is held immediately after facility and software testing and is the
basis for commissioning or accepting the information system.

	A specific type of interaction between a subject and an object that
results in the flow of information from one to the other.

access control
	The process of limiting access to the resources of a system only to
authorized programs, processes, or other systems (in a network).  Synonymous
with controlled access and limited access.

access control mechanism
	Hardware or software features, operating procedures, management
procedures, and various combinations of these designed to detect and prevent
unauthorized access and to permit authorized access in an automated system.

access level
	The hierarchical portion of the security level used to identify the
sensitivity of data and the clearance or authorization of users.  Note: The
access level, in conjunction with the nonhierarchical categories, forms the
sensitivity label of an object.  See category, security level, and sensitivity

access list
	A list of users, programs, and/or processes and the specifications
of access categories to which each is assigned.

access period
	A segment of time, generally expressed on a daily or weekly basis,
during which access rights prevail.

access port
	A logical or physical identifier that a computer uses to distinguish
different terminal input/output data streams.

access type
	The nature of an access right to a particular device, program, or
file (e.g., read, write, execute, append, modify, delete, or create).

	The property that enables activities on a system to be traced to
individuals who may then be held responsible for their actions.

	A formal declaration by the DAA that the AIS is approved to operate
in a particular security mode using a perscribed set of safeguards.
Accreditation is the official management authorization for operation of an AIS
and is based on the certification process as well as other management
considerations.  The accreditation statement affixes security responsibility
with the DAA and shows that due care has been taken for security.
accreditation authority
	Synonymous with Designated Approving Authority.

add-on security
	The retrofitting of protection mechanisms, implemented by hardware
or software.

administrative security
	The management constraints and supplemental controls established to
provide an acceptable level of protection for data.  Synonymous with
procedural security.

	A measure of confidence that the security features and architecture
of an AIS accurately mediate and enforce the security policy.

	The act of trying to bypass security controls on a system.  An
attack may be active, resulting in the alteration of data; or passive,
resulting in the release of data.  Note: The fact that an attack is made does
not necessarily mean that it will succeed.  The degree of success depends on
the vulnerability of the system or activity and the effectiveness of existing

audit trail
	A chronological record of system activities that is sufficient to
enable the reconstruction, reviewing, and examination of the sequence of
environments and activities surrounding or leading to an operation, a
procedure, or an event in a transaction from its inception to final results.

	(1) To verify the identity of a user, device, or other entity in a
computer system, often as a prerequisite to allowing access to resources in a
	 (2) To verify the integrity of data that have been stored,
transmitted, or otherwise exposed to possible unauthorized modification.

	The means used to confirm the identity or to verify the eligibility
of a station, originator, or individual.

	The granting of access rights to a user, program, or process.

automated data processing security
	Synonymous with automated information systems security.

automated information system (AIS)
	An assembly of computer hardware, software and/or firmware
configured to collect, create, communicate, compute, disseminate, process,
store, and/or control data or information.

automated information system security
	Measures and controls that protect an AIS against denial of service
and unauthorized (accidental or intentional) disclosure, modification, or
destruction of AISs and data.  AIS security includes consideration of all
hardware and/or software functions, characteristics and/or features;
operational procedures, accountability procedures, and access controls at the
central computer facility, remote computer, and terminal facilities;
management constraints; physical structures and devices; and personnel and
communication controls needed to provide an acceptable level of risk for the
AIS and for the data and information contained in the AIS.  It includes the
totality of security safeguards needed to provide an acceptable protection
level for an AIS and for data handled by an AIS.

automated security monitoring
	The use of automated procedures to ensure that security controls are
not circumvented.

availability of data

  	The state when data are in the place needed by the user, at the time
the user needs them, and in the form needed by the user.


back door
	Synonymous with trap door.

backup plan
	Synonymous with contingency plan.

Bell-La Padula model

	A formal state transition model of computer security policy that
describes a set of access control rules.  In this formal model, the entities
in a computer system are divided into abstract sets of subjects and objects.
The notion of a secure state is defined, and it is proven that each state
transition preserves security by moving from secure state to secure state,
thereby inductively proving that the system is secure.  A system state is
defined to be "secure" if the only permitted access modes of subjects to
objects are in accordance with a specific security policy.  In order to
determine whether or not a specific access mode is allowed, the clearance of a
subject is compared to the classification of the object, and a determination
is made as to whether the subject is authorized for the specific access mode.
See star property (*-property) and simple security property.

benign environment
	A nonhostile environment that may be protected from external hostile
elements by physical, personnel, and procedural security countermeasures.

between-the-lines entry

	Unauthorized access obtained by tapping the temporarily inactive
terminal of a legitimate user.  See piggyback.

beyond A1
	A level of trust defined by the DoD Trusted Computer System
Evaluation Criteria (TCSEC) that is beyond the state-of-the-art technology
available at the time the criteria were developed.  It includes all the
A1-level features plus additional ones not required at the A1 level.

	The act of searching through storage to locate or acquire
information without necessarily knowing of the existence or the format of the
information being sought.


call back
	A procedure for identifying a remote terminal.  In a call back, the
host system disconnects the caller and then dials the authorized telephone
number of the remote terminal to reestablish the connection.  Synonymous with
dial back.


	A protected identifier that both identifies the object and specifies
the access rights to be allowed to the accessor who possesses the capability.
In a capability-based system, access to protected objects such as files is
granted if the would-be accessor possesses a capability for the object.

	A restrictive label that has been applied to classified or
unclassified data as a means of increasing the protection of the data and
further restricting access to the data.

	The comprehensive evaluation of the technical and nontechnical
security features of an AIS and other safeguards, made in support of the
accreditation process, that establishes the extent to which a particular
design and implementation meet a specified set of security requirements.

closed security environment
	An environment in which both of the following conditions hold true:
(1) Application developers (including maintainers) have sufficient clearances
and authorizations to provide an acceptable presumption that they have not
introduced malicious logic.  (2) Configuration control provides sufficient
assurance that applications and the equipment are protected against the
introduction of malicious logic prior to and during the operation of system

communications security (COMSEC)
	Measures taken to deny unauthorized persons information derived from
telecommunications of the U.S.  Government concerning national security, and
to ensure the authenticity of such telecommunicatons.  Communications security
includes cryptosecurity, transmission security, emission security, and
physical security of communications security material and information.


	A class of information that has need-to-know access controls beyond
those normally provided for access to Confidential, Secret or Top Secret

compartmented security mode
	See modes of operation.

	A violation of the security policy of a system such that
unauthorized disclosure of sensitive information may have occurred.

compromising emanations
	Unintentional data-related or intelligence-bearing signals that, if
intercepted and analyzed, disclose the information transmission received,
handled, or otherwise processed by any information processing equipment.  See

computer abuse
	The misuse, alteration, disruption or destruction of data processing
resources.  The key aspect is that it is intentional and improper.

computer cryptography
	The use of a crypto-algorithm in a computer, microprocessor, or
microcomputer to perform encryption or decryption in order to protect
information or to authenticate users, sources, or information.

computer fraud
	Computer-related crimes involving deliberate misrepresentation,
alteration or disclosure of data in order to obtain something of value
(usually for monetary gain).  A computer system must have been involved in the
perpetration or coverup of the act or series of acts.  A computer system might
have been involved through improper manipulation of input data; output or
results; applications programs; data files; computer operations;
communications; or computer hardware, systems software, or firmware.

 computer security (COMPUSEC) 
	Synonymous with automated information systems security.

computer security subsystem
	A device designed to provide limited computer security features in a
larger system environment.

Computer Security Technical Vulnerability Reporting Program (CSTVRP)
	A program that focuses on technical vulnerabilities in commercially
available hardware, firmware and software products acquired by DoD.  CSTVRP
provides for the reporting, cataloging, and discreet dissemination of
technical vulnerability and corrective measure information to DoD components
on a need-to-know basis.

concealment system
	A method of achieving confidentiality in which sensitive information
is hidden by embedding it in irrelevant data.


	 The concept of holding sensitive data in confidence, limited to an
appropriate set of individuals or organizations.

configuration control
	The process of controlling modifications to the system's hardware,
firmware, software, and documentation that provides sufficient assurance that
the system is protected against the introduction of improper modifications
prior to, during, and after system implementation.  Compare configuration

configuration management
	The management of security features and assurances through control
of changes made to a system's hardware, software, firmware, documentation,
test, test fixtures and test documentation throughout the development and
operational life of the system.  Compare configuration control.

	The prevention of the leaking of sensitive data from a program.

confinement channel
	Synonymous with covert channel.

confinement property
	Synonymous with star property (*-property).

	The intermixing of data at different sensitivity and need-to-know
levels.  The lower level data is said to be contaminated by the higher level
data; thus, the contaminating (higher level) data may not receive the required
level of protection.

contingency plan
	A plan for emergency response, backup operations, and post-disaster
recovery maintained by an activity as a part of its security program that will
ensure the availability of critical resources and facilitate the continuity of
operations in an emergency situation.  Synonymous with disaster plan and
emergency plan.

control zone
	The space, expressed in feet of radius, surrounding equipment
processing sensitive information, that is under sufficient physical and
technical control to preclude an unauthorized entry or compromise.

controlled access
	See access control.

controlled sharing
	The condition that exists when access control is applied to all
users and components of a system.

cost-risk analysis
	The assessment of the costs of providing data protection for a
system versus the cost of losing or compromising the data.

	Any action, device, procedure, technique, or other measure that
reduces the vulnerability of or threat to a system.

covert channel
	A communications channel that allows two cooperating processes to
transfer information in a manner that violates the system's security policy.
Synonymous with confinement channel.

covert storage channel
	A covert channel that involves the direct or indirect writing of a
storage location by one process and the direct or indirect reading of the
storage location by another process.  Covert storage channels typically
involve a finite resource (e.g., sectors on a disk) that is shared by two
subjects at different security levels.

covert timing channel
	A covert channel in which one process signals information to another
by modulating its own use of system resources (e.g., CPU time) in such a way
that this manipulation affects the real response time observed by the second

	See DoD Trusted Computer System Evaluation Criteria.

  	 A well-defined procedure or sequence of rules or steps used to
produce a key stream or cipher text from plain text and vice versa.


  	The principles, means and methods for rendering information
unintelligible, and for restoring encrypted information to intelligible form.


 	The security or protection resulting from the proper use of
technically sound cryptosystems.


Data Encryption Standard (DES)
	A cryptographic algorithm for the protection of unclassified data,
published in Federal Information Processing Standard (FIPS) 46.  The DES,
which was approved by the National Institute of Standards and Technology, is
intended for public and government use.

data flow control
	Synonymous with  information flow control.

data integrity
	The property that data meet an a priori expectation of quality.

data security
	The protection of data from unauthorized (accidental or intentional)
modification, destruction, or disclosure.

declassification of AIS storage media
	An administrative decision or procedure to remove or reduce the
security classification of the subject media.

dedicated security mode
	See modes of operation.

default classification
	A temporary classification reflecting the highest classification
being processed in a system.  The default classification is included in the
caution statement affixed to the object.

	To reduce magnetic flux density to zero by applying a reverse
magnetizing field.

	An electrical device that can generate a magnetic field for the
purpose of degaussing magnetic storage media.  Degausser Products List (DPL)

  	 A list of commercially produced degaussers that meet National
Security Agency specifications.  This list is included in the NSA Information
Systems Security Products and Services Catalogue, and is available through the
Government Printing Office.

denial of service
	Any action or series of actions that prevent any part of a system
from functioning in accordance with its intended purpose.  This includes any
action that causes unauthorized destruction, modification, or delay of
service.  Synonymous with interdiction.

Descriptive Top-Level Specification (DTLS)

	A top-level specification that is written in a natural language
(e.g., English), an informal design notation, or a combination of the two.

Designated Approving Authority (DAA)
	The official who has the authority to decide on accepting the
security safeguards prescribed for an AIS or that official who may be
responsible for issuing an accreditation statement that records the decision
to accept those safeguards.

dial back
	Synonymous with  call back.

	The service whereby a computer terminal can use the telephone to
initiate and effect communication with a computer.

disaster plan
	Synonymous with contingency plan. 

discretionary access control (DAC)
	A means of restricting access to objects based on the identity and
need-to-know of the user, process 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.  Compare mandatory access control.

DoD Trusted Computer System Evaluation Criteria (TCSEC)
	A document published by the National Computer Security Center
containing a uniform set of basic requirements and evaluation classes for
assessing degrees of assurance in the effectiveness of hardware and software
security controls built into systems.  These criteria are intended for use in
the design and evaluation of systems that will process and/or store sensitive
or classified data.  This document is Government Standard DoD 5200.28-STD and
is frequently referred to as "The Criteria" or "The Orange Book."

	The unique context (e.g., access control parameters) in which a
program is operating; in effect, the set of objects that a subject has the
ability to access.  See process and subject.


	Security level S1 is said to dominate security level S2 if the
hierarchical classification of S1 is greater than or equal to that of S2 and
the nonhierarchical categories of S1 include all those of S2 as a subset.  


	See compromising emanations.

embedded system
	A system that performs or controls a function, either in whole or in
part, as an integral element of a larger system or subsystem.

emergency plan
	Synonymous with contingency plan.

emission security

	The protection resulting from all measures taken to deny
unauthorized persons information of value that might be derived from intercept
and from an analysis of compromising emanations from systems.

end-to-end encryption
	The protection of information passed in a telecommunications system
by cryptographic means, from point of origin to point of destination.

Endorsed Tools List (ETL)

	The list of formal verification tools endorsed by the NCSC for the
development of systems with high levels of trust.

Enhanced Hierarchical Development Methodology
	An integrated set of tools designed to aid in creating, analyzing,
modifying, managing, and documenting program specifications and proofs.  This
methology includes a specification parser and typechecker, a theorem prover,
and a multi-level security checker.  Note: This methodology is not based upon
the Hierarchical Development Methodology.

	The deliberate planting of apparent flaws in a system for the
purpose of detecting attempted penetrations.

	The aggregate of external procedures, conditions, and objects that
affect the development, operation, and maintenance of a system.

	A process by which a signal recorded on magnetic media is removed.
Erasure is accomplished in two ways: (1) by alternating current erasure, by
which the information is destroyed by applying an alternating high and low
magnetic field to the media; or (2) by direct current erasure, by which the
media are saturated by applying a unidirectional magnetic field.

Evaluated Products List (EPL)
	A list of equipments, hardware, software, and/or firmware that have
been evaluated against, and found to be technically compliant, at a particular
level of trust, with the DoD TCSEC by the NCSC.  The EPL is included in the
National Security Agency Information Systems Security Products and Services
Catalogue, which is available through the Government Printing Office.

executive state
	One of several states in which a system may operate and the only one
in which certain privileged instructions may be executed.  Such instructions
cannot be executed when the system is operating in other (e.g., user) states.
Synonymous with supervisor state.

exploitable channel
	Any information channel that is usable or detectable by subjects
external to the trusted computing base whose purpose is to violate the
security policy of the system.  See covert channel.


fail safe
	Pertaining to the automatic protection of programs and/or processing
systems to maintain safety when a hardware or software failure is detected in
a system.

fail soft
	Pertaining to the selective termination of affected nonessential
processing when a hardware or software failure is detected in a system.

failure access
	An unauthorized and usually inadvertent access to data resulting
from a hardware or software failure in the system.

failure control
	The methodology used to detect and provide fail-safe or fail-soft
recovery from hardware and software failures in a system.

	A condition that causes a device or system component to fail to
perform in a required manner.

fetch protection
	A system-provided restriction to prevent a program from accessing
data in another user's segment of storage.

file protection
	The aggregate of all processes and procedures in a system designed
to inhibit unauthorized access, contamination, or elimination of a file.

file security
	The means by which access to computer files is limited to authorized
users only.

flaw hypothesis methodology
	A systems analysis and penetration technique in which specifications
and documentation for the system are analyzed and then flaws in the system are
hypothesized.  The list of hypothesized flaws is then prioritized on the basis
of the estimated probability that a flaw exists and, assuming a flaw does
exist, on the ease of exploiting it, and on the extent of control or
compromise it would provide.  The prioritized list is used to direct a
penetration attack against the system.

flow control
	See information flow control.

formal access approval
	Documented approval by a data owner to allow access to a particular
category of information.

Formal Development Methodology
	A collection of languages and tools that enforces a rigorous method
of verification.  This methodology uses the Ina Jo specification language for
successive stages of system development, including identification and modeling
of requirements, high-level design, and program design.

formal proof
	A complete and convincing mathematical argument, presenting the full
logical justification for each proof step, for the truth of a theorem or set
of theorems.

formal security policy model
	A mathematically precise statement of a security policy.  To be
adequately precise, such a model must represent the initial state of a system,
the way in which the system progresses from one state to another, and a
definition of a "secure" state of the system.  To be acceptable as a basis for
a TCB, the model must be supported by a formal proof that if the initial state
of the system satisfies the definition of a "secure" state and if all
assumptions required by the model hold, then all future states of the system
will be secure.  Some formal modeling techniques include: state transition
models, denotational semantics models, and algebraic specification models.
See Bell-La Padula model and security policy model.

Formal Top-Level Specification (FTLS)
	A top-level specification that is written in a formal mathematical
language to allow theorems showing the correspondence of the system
specification to its formal requirements to be hypothesized and formally
proven.  formal verification
	The process of using formal proofs to demonstrate the consistency
between a formal specification of a system and a formal security policy model
(design verification) or between the formal specification and its high level
program implementation (implementation verification).

front-end security filter
	A security filter, which could be implemented in hardware or
software, that is logically separated from the remainder of the system to
protect the system's integrity.

functional testing
	The segment of security testing in which the advertised security
mechanisms of the system are tested, under operational conditions, for correct


	An expression of the relative size of a data object; e.g.,
protection at the file level is considered coarse granularity, whereas
protection at field level is considered to be of a finer granularity.

	A processor that provides a filter between two disparate systems
operating at different security levels or between a user terminal and a data
base to filter out data that the user is not authorized to access.

Gypsy Verification Environment
	An integrated set of tools for specifying, coding, and verifying
programs written in the Gypsy language, a language similar to Pascal which has
both specification and programming features.  This methology includes an
editor, a specification processor, a verification condition generator, a
user-directed theorem prover, and an information flow tool.


handshaking procedure
	A dialogue between two entities (e.g., a user and a computer, a
computer and another computer, or a program and another program) for the
purpose of identifying and authenticating the entities to one another.

Hierarchical Development Methodology
	A methodology for specifying and verifying the design programs
written in the Special specification language.  The tools for this methodology
include the Special specification processor, the Boyer-Moore theorem prover,
and the Feiertag information flow tool.

host to front-end protocol
	A set of conventions governing the format and control of data that
are passed from a host to a front-end machine.  


	The process that enables recognition of an entity by a system,
generally by the use of unique machine-readable user names.

	Synonymous with spoofing.

incomplete parameter checking
	A system design flaw that results when all parameters have not been
fully anticipated for accuracy and consistency, thus making the system
vulnerable to penetration.

individual accountability
	The ability to associate positively the identity of a user with the
time, method, and degree of access to a system.

information flow control
	A procedure to ensure that information transfers within a system are
not made from a higher security level object to an object of a lower security
level.  See covert channel, simple security property, star property
(*-property).  Synonymous with data flow control and flow control.

Information System Security Officer (ISSO)

 	The person responsible to the DAA for ensuring that security is
provided for and implemented throughout the life cycle of an AIS from the
beginning of the concept development plan through its design, development,
operation, maintenance, and secure disposal.

Information Systems Security Products and Services Catalogue

 	A catalogue issued quarterly by the National Security Agency that
incorporates the DPL, EPL, ETL, PPL and other security product and service
lists.  This catalogue is available through the U.S.  Government Printing
Office, Washington, DC 20402, (202) 783-3238.

	Sound, unimpaired or perfect condition.
	See denial of service.

internal security controls
	Hardware, firmware, and software features within a system that
restrict access to resources (hardware, software, and data) to authorized
subjects only (persons, programs, or devices).

	The containment of subjects and objects in a system in such a way
that they are separated from one another, as well as from the protection
controls of the operating system.  


This document contains no entries beginning with the letter. 


This document contains no entries beginning with the letter.


least privilege
	The principle that requires that each subject be granted the most
restrictive set of privileges needed for the performance of authorized tasks.
The application of this principle limits the damage that can result from
accident, error, or unauthorized use.

limited access
	Synonymous with access control.


	A computer protection system in which each protected object has a
list of all subjects authorized to access it.  Compare ticket-oriented.

lock-and-key protection system
	A protection system that involves matching a key or password with a
specific access requirement.

logic bomb
	A resident computer program that triggers the perpetration of an
unauthorized act when particular states of the system are realized.

	An error of omission or oversight in software or hardware that
permits circumventing the system security policy.  


magnetic remanence
	A measure of the magnetic flux density remaining after removal of
the applied magnetic force.  Refers to any data remaining on magnetic storage
media after removal of the power.

maintenance hook
	Special instructions in software to allow easy maintenance and
additional feature development.  These are not clearly defined during access
for design specification.  Hooks frequently allow entry into the code at
unusual points or without the usual checks, so they are a serious security
risk if they are not removed prior to live implementation.  Maintenance hooks
are special types of trap doors.

malicious logic
	Hardware, software, or firmware that is intentionally included in a
system for an unauthorized purpose; e.g., a Trojan horse.

mandatory access control (MAC)
	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.  Compare discretionary access control.

	Synonymous with spoofing.

	Synonymous with spoofing.

modes of operation
	A description of the conditions under which an AIS functions, based
on the sensitivity of data processed and the clearance levels and
authorizations of the users.  Four modes of operation are authorized:

		(1)  Dedicated Mode
		An AIS is operating in the dedicated mode when each user
with direct or indirect individual access to the AIS, its peripherals, remote
terminals, or remote hosts, has all of the following: 
			a.  A valid personnel
clearance for all information on the system.
			b.  Formal access approval for, and has signed
nondisclosure agreements for all the information stored and/or processed
(including all compartments, subcompartments and/or special access programs).
			c.  A valid need-to-know for all information
contained within the system.

		(2)  System-High Mode
		An AIS is operating in the system-high mode when each user
with direct or indirect access to the AIS, its peripherals, remote terminals,
or remote hosts has all of the following:
			a.  A valid personnel clearance for all
information on the AIS.
			b.  Formal access approval for, and has signed
nondisclosure agreements for all the information stored and/or processed
(including all compartments, subcompartments, and/or special access programs).

			c.  A valid need-to-know for some of the
information contained within the AIS.

		(3)  Compartmented Mode
		An AIS is operating in the compartmented mode when each
user with direct or indirect access to the AIS, its peripherals, remote
terminals, or remote hosts, has all of the following:
			a.  A valid personnel clearance for the most
restricted information processed in the AIS.
			b.  Formal access approval for, and has signed
nondisclosure agreements for that information to which he/she is to have
			c.  A valid need-to-know for that information to
which he/she is to have access.

		(4)  Multilevel Mode
		An AIS is operating in the multilevel mode when all the
following statements are satisfied concerning the users with direct or
indirect access to the AIS, its peripherals, remote terminals, or remote
			a.  Some do not have a valid personnel clearance
for all the information processed in the AIS.
			b.  All have the proper clearance and have the
appropriate formal access approval for that information to which he/she is to
have access.
			c.  All have a valid need-to-know for that
information to which they are to have access.

multilevel device

	A device that is used in a manner that permits it to simultaneously
process data of two or more security levels without risk of compromise.  To
accomplish this, sensitivity labels are normally stored on the same physical
medium and in the same form (i.e., machine-readable or human-readable) as the
data being processed.

multilevel secure

	A class of system containing information with different
sensitivities that simultaneously permits access by users with different
security clearances and needs-to-know, but prevents users from obtaining
access to information for which they lack authorization.

multilevel security mode

	See modes of operation.

multiple access rights terminal
	A terminal that may be used by more than one class of users; for
example, users with different access rights to data.

multiuser mode of operation
	A mode of operation designed for systems that process sensitive
unclassified information in which users may not have a need-to-know for all
information processed in the system.  This mode is also for microcomputers
processing sensitive unclassified information that cannot meet the
requirements of the stand-alone mode of operation.

mutually suspicious
	The state that exists between interacting processes (subsystems or
programs) in which neither process can expect the other process to function
securely with respect to some property.


National Computer Security Assessment Program
	A program designed to evaluate the interrelationship of empirical
data of computer security infractions and critical systems profiles, while
comprehensively incorporating information from the CSTVRP.  The assessment
will build threat and vulnerability scenarios that are based on a collection
of facts from relevant reported cases.  Such scenarios are a powerful,
dramatic, and concise form of representing the value of loss experience

National Computer Security Center (NCSC)
	Originally named the DoD Computer Security Center, the NCSC is
responsible for encouraging the widespread availability of trusted computer
systems throughout the Federal Government.

National Security Decision Directive 145 (NSDD 145)
	Signed by President Reagan on l7 September l984, this directive is
entitled "National Policy on Telecommunications and Automated Information
Systems Security." It provides initial objectives, policies, and an
organizational structure to guide the conduct of national activities toward
safeguarding systems that process, store, or communicate sensitive
information; establishes a mechanism for policy development; and assigns
implementation responsibilities.

National Telecommunications and Information Systems Security Advisory
Memoranda/ Instructions (NTISSAM, NTISSI)

	NTISS Advisory Memoranda and Instructions provide advice,
assistance, or information of general interest on telecommunications and
systems security to all applicable federal departments and agencies.
NTISSAMs/NTISSIs are promulgated by the National Manager for
Telecommunications and Automated Information Systems Security and are

National Telecommunications and Information System Security Directives (NTISSD)
	NTISS Directives establish national-level decisions relating to
NTISS policies, plans, programs, systems, or organizational delegations of
authority.  NTISSDs are promulgated by the Executive Agent of the Government
for Telecommunications and Information Systems Security, or by the Chairman of
the NTISSC when so delegated by the Executive Agent.  NTISSDs are binding upon
all federal departments and agencies.


	The necessity for access to, knowledge of, or possession of specific
information required to carry out official duties.

network front end
	A device that implements the necessary network protocols, including
security-related protocols, to allow a computer system to be attached to a

NSDD 145

 	See National Security Decision Directive 145.


	A passive entity that contains or receives information.  Access to
an object potentially implies access to the information it contains.  Examples
of objects are: records, blocks, pages, segments, files, directories,
directory trees, and programs, as well as bits, bytes, words, fields,
processors, video displays, keyboards, clocks, printers, and network nodes.

object reuse
	The reassignment and reuse of a storage medium (e.g., page frame,
disk sector, magnetic tape) that once contained one or more objects.  To be
securely reused and assigned to a new subject, storage media must contain no
residual data (magnetic remanence) from the object(s) previously contained in
the media.

open security environment
	An environment that includes those systems in which at least one of
the following conditions holds true: (l) Application developers (including
maintainers) do not have sufficient clearance or authorization to provide an
acceptable presumption that they have not introduced malicious logic.  (2)
Configuration control does not provide sufficient assurance that applications
are protected against the introduction of malicious logic prior to and during
the operation of system applications.

Operations Security (OPSEC)

	An analytical process by which the U.S.  Government and its
supporting contractors can deny to potential adversaries information about
capabilities and intentions by identifying, controlling, and protecting
evidence of the planning and execution of sensitive activities and operations.

Orange Book 

	Alternate name for DoD Trusted Computer Security Evaluation

overt channel
	A path within a computer system or network that is designed for the
authorized transfer of data.  Compare covert channel.

overwrite procedure
	A stimulation to change the state of a bit followed by a known
pattern.  See magnetic remanence.


partitioned security mode
	A mode of operation wherein all personnel have the clearance but not
necessarily formal access approval and need-to-know for all information
contained in the system.  Not to be confused with compartmented security mode.

	A protected/private character string used to authenticate an

	The successful act of bypassing the security mechanisms of a system.

penetration signature
	The characteristics or identifying marks that may be produced by a

penetration study
	A study to determine the feasibility and methods for defeating
controls of a system.

penetration testing
	The portion of security testing in which the evaluators attempt to
circumvent the security features of a system.  The evaluators may be assumed
to use all system design and implementation documentation, which may include
listings of system source code, manuals, and circuit diagrams.  The evaluators
work under the same constraints applied to ordinary users.

periods processing
	The processing of various levels of sensitive information at
distinctly different times.  Under periods processing, the system must be
purged of all information from one processing period before transitioning to
the next when there are different users with differing authorizations.

	A description of the type of authorized interactions a subject can
have with an object.  Examples include: read, write, execute, add, modify, and

personnel security
	The procedures established to ensure that all personnel who have
access to sensitive information have the required authority as well as
appropriate clearances.

physical security

	The application of physical barriers and control procedures as
preventive measures or countermeasures against threats to resources and
sensitive information.

	Gaining unauthorized access to a system via another user's
legitimate connection.  See between-the-lines entry.

Preferred Products List (PPL)
	A list of commercially produced equipments that meet TEMPEST and
other requirements prescribed by the National Security Agency.  This list is
included in the NSA Information Systems Security Products and Services
Catalogue, issued quarterly and available through the Government Printing

print suppression
 	Eliminating the displaying of characters in order to preserve their
secrecy; e.g., not displaying the characters of a password as it is keyed at
the input terminal.

privileged instructions
	A set of instructions (e.g., interrupt handling or special computer
instructions) to control features (such as storage protection features) that
are generally executable only when the automated system is operating in the
executive state.

procedural security
	Synonymous with administrative security.


 	 A program in execution. See domain and subject.

protection philosophy
	An informal description of the overall design of a system that
delineates each of the protection mechanisms employed.  A combination,
appropriate to the evaluation class, of formal and informal techniques is used
to show that the mechanisms are adequate to enforce the security policy.

protection ring
	One of a hierarchy of privileged modes of a system that gives
certain access rights to user programs and processes authorized to operate in
a given mode.

protection-critical portions of the TCB
	Those portions of the TCB whose normal function is to deal with the
control of access between subjects and objects.  Their correct operation is
essential to the protection of the data on the system.

	A set of rules and formats, semantic and syntactic, that permits
entities to exchange information.

	An apparent loophole deliberately implanted in an operating system
program as a trap for intruders.

Public Law 100-235 (P.L. 100-235)

	Also known as the Computer Security Act of 1987, this law creates a
means for establishing minimum acceptable security practices for improving the
security and privacy of sensitive information in federal computer systems.
This law assigns to the National Institute of Standards and Technology
responsibility for developing standards and guidelines for federal computer
systems processing unclassified data.  The law also requires establishment of
security plans by all operators of federal computer systems that contain
sensitive information.

	The removal of sensitive data from an AIS, AIS storage device, or
peripheral device with storage capacity, at the end of a processing period.
This action is performed in such a way that there is assurance proportional to
the sensitivity of the data that the data may not be reconstructed.  An AIS
must be disconnected from any external network before a purge.  After a purge,
the medium can be declassified by observing the review procedures of the
respective agency.


This document contains no entries beginning with the letter.


	A fundamental operation that results only in the flow of information
from an object to a subject.

read access
	Permission to read information.

recovery procedures
	The actions necessary to restore a system's computational capability
and data files after a system failure.

reference monitor concept
	An access-control concept that refers to an abstract machine that
mediates all accesses to objects by subjects.

reference validation mechanism
	An implementation of the reference monitor concept.  A security
kernel is a type of reference validation mechanism.

	The probability of a given system performing its mission adequately
for a specified period of time under the expected operating conditions.

residual risk
	The portion of risk that remains after security measures have been

	Data left in storage after processing operations are complete, but
before degaussing or rewriting has taken place.

resource encapsulation
	The process of ensuring that a resource not be directly accessible
by a subject, but that it be protected so that the reference monitor can
properly mediate accesses to it.  

restricted area
	Any area to which access is subject to special restrictions or
controls for reasons of security or safeguarding of property or material.

	The probability that a particular threat will exploit a particular
vulnerability of the system.

risk analysis
	The process of identifying security risks, determining their
magnitude, and identifying areas needing safeguards.  Risk analysis is a part
of risk management.  Synonymous with risk assessment.

risk assessment

  	 Synonymous with risk analysis.

risk index
	The disparity between the minimum clearance or authorization of
system users and the maximum sensitivity (e.g., classification and categories)
of data processed by a system.  See CSC-STD-003-85 and CSC-STD-004-85 for a
complete explanation of this term.

risk management
	The total process of identifying, controlling, and eliminating or
minimizing uncertain events that may affect system resources.  It includes
risk analysis, cost benefit analysis, selection, implementation and test,
security evaluation of safeguards, and overall security review.  


	See security safeguards.

	Searching through object residue to acquire unauthorized data.

secure configuration management
	The set of procedures appropriate for controlling changes to a
system's hardware and software structure for the purpose of ensuring that
changes will not lead to violations of the system's security policy.

secure state
	A condition in which no subject can access any object in an
unauthorized manner.

secure subsystem
	A subsystem that contains its own implementation of the reference
monitor concept for those resources it controls.  However, the secure
subsystem must depend on other controls and the base operating system for the
control of subjects and the more primitive system objects.

security critical mechanisms
	Those security mechanisms whose correct operation is necessary to
ensure that the security policy is enforced.

security evaluation
	An evaluation done to assess the degree of trust that can be placed
in systems for the secure handling of sensitive information.  One type, a
product evaluation, is an evaluation performed on the hardware and software
features and assurances of a computer product from a perspective that excludes
the application environment.  The other type, a system evaluation, is done for
the purpose of assessing a system's security safeguards with respect to a
specific operational mission and is a major step in the certification and
accreditation process.

security fault analysis
	A security analysis, usually performed on hardware at gate level, to
determine the security properties of a device when a hardware fault is

security features
	The security-relevant functions, mechanisms, and characteristics of
system hardware and software.  Security features are a subset of system
security safeguards.

security filter
	A trusted subsystem that enforces a security policy on the data that
pass through it.

security flaw
 	An error of commission or omission in a system that may allow
protection mechanisms to be bypassed.

security flow analysis
	A security analysis performed on a formal system specification that
locates potential flows of information within the system.
security kernel
	The hardware, firmware, and software elements of a TCB that
implement the reference monitor concept.  It must mediate all accesses, be
protected from modification, and be verifiable as correct.

security label

  	 A piece of information that represents the security level of an

security level
	The combination of a hierarchical classification and a set of
nonhierarchical categories that represents the sensitivity of information.

security measures
	Elements of software, firmware, hardware, or procedures that are
included in a system for the satisfaction of security specifications.

security perimeter
	The boundary where security controls are in effect to protect

security policy

	The set of laws, rules, and practices that regulate how an
organization manages, protects, and distributes sensitive information.

security policy model
	A formal presentation of the security policy enforced by the system.
It must identify the set of rules and practices that regulate how a system
manages, protects, and distributes sensitive information.  See Bell-La Padula
model and formal security policy model.

security range
	The highest and lowest security levels that are permitted in or on a
system, system component, subsystem or network.

security requirements
	The types and levels of protection necessary for equipment, data,
information, applications, and facilities to meet security policy.

security requirements baseline
	A description of minimum requirements necessary for a system to
maintain an acceptable level of security.

security safeguards
	The protective measures and controls that are prescribed to meet the
security requirements specified for a system.  Those safeguards may include
but are not necessarily limited to: hardware and software security features,
operating procedures, accountability procedures, access and distribution
controls, management constraints, personnel security, and physical structures,
areas, and devices.  Also called safeguards.

security specifications
	A detailed description of the safeguards required to protect a

security test and evaluation
	An examination and analysis of the security safeguards of a system
as they have been applied in an operational environment to determine the
security posture of the system.

security testing
	A process used to determine that the security features of a system
are implemented as designed.  This includes hands-on functional testing,
penetration testing, and verification.

sensitive information
	Any information, the loss, misuse, modification of, or unauthorized
access to, could affect the national interest or the conduct of Federal
programs, or the privacy to which individuals are entitled under Section 552a
of Title 5, U.S.  Code, but that has not been specifically authorized under
criteria established by an Executive order or an act of Congress to be kept
classified in the interest of national defense or foreign policy.

 sensitivity label
	A piece of information that represents the security level of an
object.  Sensitivity labels are used by the TCB as the basis for mandatory
access control decisions.

simple security condition
	See simple security property.

simple security property
	A Bell-La Padula security model rule allowing a subject read access
to an object only if the security level of the subject dominates the security
level of the object.  Synonymous with simple security condition.

single-level device

	An automated information systems device that is used to process data
of a single security level at any one time.

Software Development Methodologies

	Methodologies for specifying and verifying design programs for
system development.  Each methodology is written for a specific computer
language.  See Enhanced Hierarchical Development Methodology, Formal
Development Methodology, Gypsy Verification Environment and Hierarchical
Development Methodology.

software security

 	General purpose (executive, utility or software development tools)
and applications programs or routines that protect data handled by a system.

software system test and evaluation process

 	A process that plans, develops and documents the quantitative
demonstration of the fulfillment of all baseline functional performance,
operational and interface requirements.
	An attempt to gain access to a system by posing as an authorized
user.  Synonymous with impersonating, masquerading or.mimicking.

stand-alone, shared system
	A system that is physically and electrically isolated from all other
systems, and is intended to be used by more than one person, either
simultaneously (e.g., a system with multiple terminals) or serially, with data
belonging to one user remaining available to the system while another user is
using the system (e.g., a personal computer with nonremovable storage media
such as a hard disk).

stand-alone, single-user system
	A system that is physically and electrically isolated from all other
systems, and is intended to be used by one person at a time, with no data
belonging to other users remaining in the system (e.g., a personal computer
with removable storage media such as a floppy disk).

star property 
	See *-property, page 2.

State Delta Verification System
	A system designed to give high confidence regarding microcode
performance by using formulae that represent isolated states of a computation
to check proofs concerning the course of that computation.

state variable
	A variable that represents either the state of the system or the
state of some system resource.

storage object
	An object that supports both read and write accesses.

Subcommittee on Automated Information Systems Security (SAISS)
	NSDD-145 authorizes and directs the establishment, under the NTISSC,
of a permanent Subcommittee on Automated Information Systems Security.  The
SAISS is composed of one voting member from each organization represented on

Subcommittee on Telecommunications Security (STS)
	NSDD-145 authorizes and directs the establishment, under the NTISSC,
of a permanent Subcommittee on Telecommunications Security.  The STS is
composed of one voting member from each organization represented on the

	An active entity, generally in the form of a person, process, or
device, that causes information to flow among objects or changes the system
state.  Technically, a process/domain pair.

subject security level
	A subjects security level is equal to the security level of the
objects to which it has both read and write access.  A subjects security level
must always be dominated by the clearance of the user with which the subject
is associated.

supervisor state
	Synonymous with executive state.

System Development Methodologies

 	Methodologies developed through software engineering to manage the
complexity of system development.  Development methodologies include software
engineering aids and high-level design analysis tools.

system high security mode

	See modes of operation.

 system integrity
	The quality that a system has when it performs its intended function
in an unimpaired manner, free from deliberate or inadvertent unauthorized
manipulation of the system.

system low
	The lowest security level supported by a system at a particular time
or in a particular environment.

System Security Officer (SSO)
	See Information System Security Officer. 

Systems Security Steering Group
	The senior government body established by NSDD-145 to provide
top-level review and policy guidance for the telecommunications security and
automated information systems security activities of the U.S.  Government.
This group is chaired by the Assistant to the President for National Security
Affairs and consists of the Secretary of State, Secretary of Treasury, the
Secretary of Defense, the Attorney General, the Director of the Office of
Management and Budget, and the Director of Central Intelligence.


	An unauthorized modification that alters the proper functioning of
an equipment or system in a manner that degrades the security or functionality
it provides.

technical attack
	An attack that can be perpetrated by circumventing or nullifying
hardware and software protection mechanisms, rather than by subverting system
personnel or other users.

technical vulnerability
	A hardware, firmware, communication, or software flaw that leaves a
computer processing system open for potential exploitation, either externally
or internally, thereby resulting in risk for the owner, user, or manager of
the system.

	The study and control of spurious electronic signals emitted by
electrical equipment.

terminal identification
	The means used to uniquely identify a terminal to a system.

	Any circumstance or event with the potential to cause harm to a
system in the form of destruction, disclosure, modification of data, and/or
denial of service.

threat agent
	A method used to exploit a vulnerability in a system, operation, or

threat analysis
	The examination of all actions and events that might adversely
affect a system or operation.

threat monitoring
	The analysis, assessment, and review of audit trails and other data
collected for the purpose of searching out system events that may constitute
violations or attempted violations of system security.

	A computer protection system in which each subject maintains a list
of unforgeable bit patterns, called tickets, one for each object the subject
is authorized to access.  Compare list-oriented.

time-dependent password
	A password that is valid only at a certain time of day or during a
specified interval of time.

top-level specification
	A nonprocedural description of system behavior at the most abstract
level; typically, a functional specification that omits all implementation

	A security model rule stating that the security level of an object
cannot change while the object is being processed by an AIS.

trap door
	A hidden software or hardware mechanism that can be triggered to
permit system protection mechanisms to be circumvented.  It is activated in
some innocent-appearing manner; e.g., a special "random" key sequence at a
terminal.  Software developers often introduce trap doors in their code to
enable them to reenter the system and perform certain functions.  Synonymous
with back door.

Trojan horse
	A computer program with an apparently or actually useful function
that contains additional (hidden) functions that surreptitiously exploit the
legitimate authorizations of the invoking process to the detriment of security
or integrity.

trusted computer system
	A system that employs sufficient hardware and software assurance
measures to allow its use for simultaneous processing of a range of sensitive
or classified information.
Trusted Computing Base (TCB)
	The totality of protection mechanisms within a computer system,
including hardware, firmware, and software, the combination of which is
responsible for enforcing a security policy.  A TCB consists of one or more
components that together enforce a unified security policy over a product or
system.  The ability of a TCB to enforce correctly a unified security policy
depends solely on the mechanisms within the TCB and on the correct input by
system administrative personnel of parameters (e.g., a user's clearance level)
related to the security policy.

trusted distribution

 	 A trusted method for distributing the TCB hardware, software, and
firmware components, both originals and updates, that provides methods for
protecting the TCB from modification during distribution and for detection of
any changes to the TCB that may occur.

 trusted identification forwarding
	An identification method used in networks whereby the sending host
can verify that an authorized user on its system is attempting a connection to
another host.  The sending host transmits the required user authentication
information to the receiving host.  The receiving host can then verify that
the user is validated for access to its system.  This operation may be
transparent to the user.

trusted path
 	 A mechanism by which a person at a terminal can communicate
directly with the TCB.  This mechanism can only be activated by the person or
the TCB and cannot be imitated by untrusted software.
trusted process
	A process whose incorrect or malicious execution is capable of
violating system security policy.

trusted software
	The software portion of the TCB. 


untrusted process
	A process that has not been evaluated or examined for adherence to
the secuity policy.  It may include incorrect or malicious code that attempts
to circumvent the security mechanisms.


	Person or process accessing an AIS either by direct connections
(i.e., via terminals), or indirect connections (i.e., prepare input data or
receive output that is not reviewed for content or classification by a
responsible individual).

user ID
	A unique symbol or character string that is used by a system to
identify a specific user.

user profile
	Patterns of a user's activity that can be used to detect changes in
normal routines.  


	The process of comparing two levels of system specification for
proper correspondence (e.g., security policy model with top-level
specification, top-level specification with source code, or source code with
object code).  This process may or may not be automated.

	A self-propagating Trojan horse, composed of a mission component, a
trigger component, and a self-propagating component.

	A weakness in system security procedures, system design,
implementation, internal controls, etc., that could be exploited to violate
system security policy.

vulnerability analysis
	The systematic examination of systems in order to determine the
adequacy of security measures, identify security deficiencies, and provide
data from which to predict the effectiveness of proposed security measures.

vulnerability assessment

 	A measurement of vulnerability which includes the susceptibility of
a particular system to a specific attack and the opportunities available to a
threat agent to mount that attack.  


work factor

	An estimate of the effort or time needed by a potential penetrator
with specified expertise and resources to overcome a protective measure.


	A fundamental operation that results only in the flow of information
from a subject to an object.

write access

	Permission to write to an object.


This document contains no entries beginning with the letters  X, Y, or Z.