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.

CERT: The Computer Emergency Response Team was established at Carnegie-Mellon University after the 1988 Internet worm attack.

Certificate: Digital equivalent of an identity card. It contains, among other things, the name of its owner, the name of the issuing authority, a validity period, and the public part of an asymmetric key pair. With the digital signature from the certification authority, the public key is uniquely linked to its user.

Certification Body: An independent and impartial national organization that performs certification. Also referred to as an evaluation body or entity.

Certificate Path: In PKIs, certificates are arranged in a hierarchical structure. The root certification authority's certificate is on the uppermost node. This certification authority certifies other certification authorities where necessary. User certificates are located at the bottom of the hierarchy. So that all users can communicate with each other within this hierarchy, each participant needs the certificate path to the root certification authority. This enables all users to check any certificate within this hierarchy for authenticity and validity.

Certificate Revocation List (CRL): List of certificates that have been declared invalid before their expiry date by the issuing CA. The CA maintains this list and is obliged to publish it, i.e. update it regularly and put it at the disposal of all participants.

Challenge/Response: A security procedure in which one communicator requests authentication of another communicator, and the latter replies with a pre-established appropriate reply.

Channel: An information transfer path within a system. May also refer to the mechanism by which the path is effected.

Chroot: A technique under UNIX whereby a process is permanently restricted to an isolated subset of the file system.

Cipher: A cipher is an encryption-decryption algorithm.

Ciphertext: Ciphertext is the product of encryption. It is text that has been encoded in such a way, that it can only be decoded again by individuals possessing the appropriate key.

Client/Device: Hardware that retrieves information from a server.

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 and (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 applications.

Closed User Group: A closed user group permits users belonging to a group to communicate with each other, but precludes communications with other users who are not members of the group.

Clustering: Group of independent systems working together as a single system. Clustering technology allows groups of servers to access a single disk array containing applications and data.

Cluster Virus: A virus that infects disks or diskettes by modifying their file systems so that every program file entry points to the virus code. The virus code only exists in one physical place on the disk, but running any program on the disk will run the virus as well. So, cluster viruses can appear to infect every program on a disk.

Coded File: In encryption, a coded file contains unreadable information.

COM File: A PC-DOS binary image that is loaded into memory. It has restrictions in size and method of program load. It generally loads somewhat faster than an EXE file and has a simpler structure.

Combined Evaluation: Method using proxy and state or filter evaluations as allowed by administrator.

Communication Channel: The physical media and devices which provide the means for transmitting information from one component of a network to (one or more) other components.

Communication Link: The physical means of connecting one location to another for the purpose of transmitting and/or receiving data.

Communications Security (COMSEC): Measures taken to deny unauthorized persons information derived from telecommunications of an entity concerning national or organizational security, and to ensure the authenticity of such telecommunications. Communications security includes cryptosecurity, transmission security, emission security, and physical security of communications security material and information.

Communications Server: Procedures designed to ensure that telecommunications messages maintain their integrity and are not accessible by unauthorized individuals.

Companion Virus: A virus that creates a new program with the same file name as an existing program, but in a different place or with a different file type, so that typing the program's name on the command line causes the virus program to be executed instead of the original program. For instance, a companion virus could create a file name FOO.COM that contained its code, if a program named FOO.EXE already existed. When the user types FOO on the command line, FOO.COM would get executed instead of FOO.EXE.

Compartment: A designation applied to a type of sensitive information, indicating the special handling procedures to be used for the information and the general class of people who may have access to the information. It can refer to the designation of information belonging to one or more categories.

Compromise: A violation of the security system such that an 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.

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

Computer Architecture: The set of layers and protocols (including formats and standards that different hardware/software must comply with to achieve stated objectives) which define a computer system. Computer architecture features can be available to application programs and system programmers in several modes, including a protected mode. For example, the system-level features of computer architecture may include: (1) memory management, (2) protection, (3) multitasking, (4) input/output, (5) exceptions and multiprocessing, (6) initialization, (7) co-processing and multiprocessing, (8) debugging, and (9) cache management.

Computer Cryptography: The use of a cryptoalgorithm in a computer, microprocessor, or microcomputer to perform encryption or decryption in order to protect information or to authenticate users, sources, or information.

Computer Security: Technological and managerial procedures applied to computer systems to ensure the availability, integrity and confidentiality of information managed by the computer system.

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.

Confidentiality: A message is confidential when its contents can only be read by authorized recipients. Without encryption, message contents can be read by third parties, unnoticed by sender and addressee. By using powerful encryption algorithms it is guaranteed that only entitled recipients can read the contents.

Configuration: Selection of one of the sets of possible combinations of features of a system.

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 management below...

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.

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

Cookie: The most common meaning of "Cookie" on the Internet refers to a piece of information sent by a Web Server to a Web Browser that the Browser software is expected to save and to send back to the Server whenever the browser makes additional requests from the Server. Depending on the type of Cookie used, and the Browser's settings, the Browser may accept or not accept the Cookie, and may save the Cookie for either a short time or a long time.

Cross Certification: Process where a CA of one PKI issues a certificate on the public key of a CA of another PKI. Establishes interoperability, since certificates of the latter PKI can be verified by individuals of the former PKI.

Cracker: A cracker is someone who breaks into someone else's computer system, often on a network. A cracker can be doing this for profit, maliciously, for some altruistic purpose or cause, or because the challenge is there. Some breaking-and-entering has been done ostensibly to point out weaknesses in a site's security system.

CRC:Cyclic Redundancy Code. A CRC is a type of checksum. A checksum algorithm takes a file (or other string of bytes) and calculates from it a few bytes (the checksum) that depend on the entire file. The idea is that, if anything in the file changes, the checksum will change. CRC checksums are usually used to detect random, uncorrelated changes in files.

Cryptanalysis: Study of how to defeat (compromise) cryptographic mechanisms. See also: 'Cryptography' and 'Cryptology' below...

Cryptography: Mathematical discipline that is concerned with finding methods for keeping communications private, unimpaired, and authentic. Today's cryptography is based on the existence of mathematical problems that are believed (by experts) to be difficult.

Cryptosystem: A cryptosystem is a system for encrypting and decrypting data. Encryption involves an algorithm for combining the original data (plaintext) with one or more keys -- numbers or strings of characters known only to the sender and/or recipient. The resulting output is known as ciphertext. The security of a cryptosystem usually depends on the secrecy of (some of) the keys rather than on the supposed secrecy of the algorithm. A strong cryptosystem has a large range of possible keys so that it is not possible to just try all possible keys. A strong cryptosystem will produce Ciphertext that appears random to all standard statistical tests. A strong cryptosystem will resist all known previous methods for breaking codes (cryptanalysis).

Cryptographic Checksum: A one-way function applied to a file to produce a unique "fingerprint" of the file for later reference. Checksum systems are a primary means of detecting file system tampering on UNIX.

Cryptware: Software that allows performing encryption. and/or decryption of data