Specifies entity authentication mechanisms using symmetric encipherment algorithms. Four of the mechanisms provide entity authentication between two entities where no trusted third party is involved; two of these are mechanisms to unilaterally authenticate one entity to another, while the other two are mechanisms for mutual authentication of two entities. The remaining mechanisms require a trusted third party for the establishment of a common secret key, and realize mutual or unilateral entity authentication. The mechanisms specified in ISO/IEC 9798-2:2008 use time variant parameters such as time stamps, sequence numbers, or random numbers to prevent valid authentication information from being accepted at a later time or more than once.
