Table 1: Some of the notations used in Chen et al.'s protocol.

Symbol Definition

Identities of users and , respectively
Identity of the authentication server
The large primes and , a generator of group with the order
The long-term key of , and
Components of authentication information and
Random number privately chosen by and , respectively
Components of session key, where and
Collision-free one-way hash function
Evidence generated by user for user