This part of ISO/IEC 9798 specifies entity authentication mechanisms using digital signatures based on asymmetric techniques. Two mechanisms are concerned with the authentication of a single entity (unilateral authentication), while the remaining are mechanisms for mutual authentication of two entities. A digital signature is used to verify the identity of an entity. A trusted third party may be involved.The mechanisms specified in this part of ISO/IEC 9798 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.If a time stamp or a sequence number