Table 1.3 lists the security mechanisms defined in X.800. As can be seen the mechanisms are divided into those that are implemented in a specific protocol layer and those that are not specific to any particular protocol layer or security service. These mechanisms will be covered in the appropriate places in the book and so we do not elaborate now, except to comment on the definition of encipherment. X.800 distinguishes between reversible encipherment mechanisms and irreversible encipherment mechanisms. A reversible encipherment mechanism is simply an encryption algorithm that allows data to be encrypted and subsequently decrypted. Irreversible encipherment mechanisms include hash algorithms and message authentication codes, which are used in digital signature and message authentication applications.
Table 1.3. Security Mechanisms (X.800)
SPECIFIC SECURITY MECHANISMS |
May be incorporated into the appropriate protocol layer in order to provide some of the OSI security services. |
Encipherment |
The use of mathematical algorithms to transform data into a form that is not readily intelligible. The transformation and subsequent recovery of the data depend on an algorithm and zero or more encryption keys. |
Digital Signature |
Data appended to, or a cryptographic transformation of, a data unit that allows a recipient of the data unit to prove the source and integrity of the data unit and protect against forgery (e.g., by the recipient). |
Access Control |
A variety of mechanisms that enforce access rights to resources. |
Data Integrity |
A variety of mechanisms used to assure the integrity of a data unit or stream of data units. |
Authentication Exchange |
A mechanism intended to ensure the identity of an entity by means of information exchange. |
Traffic Padding |
The insertion of bits into gaps in a data stream to frustrate traffic analysis attempts. |
Routing Control |
Enables selection of particular physically secure routes for certain data and allows routing changes, especially when a breach of security is suspected. |
Notarization |
The use of a trusted third party to assure certain properties of a data exchange. |
PERVASIVE SECURITY MECHANISMS |
Mechanisms that are not specific to any particular OSI security service or protocol layer. |
Trusted Functionality |
That which is perceived to be correct with respect to some criteria (e.g., as established by a security policy). |
Security Label |
The marking bound to a resource (which may be a data unit) that names or designates the security attributes of that resource. |
Event Detection |
Detection of security-relevant events. |
Security Audit Trail |
Data collected and potentially used to facilitate a security audit, which is an independent review and examination of system records and activities. |
Security Recovery |
Deals with requests from mechanisms, such as event handling and management functions, and takes recovery actions. |
Table 1.4, based on one in X.800, indicates the relationship between security services and security mechanisms.