Cryptanalysis of a Provably Secure Gateway-Oriented Password-Based Authenticated Key Exchange Protocol

Recently, Chien et al. proposed a gateway-oriented password-based authenticated key exchange (GPAKE) protocol, through which a client and a gateway could generate a session key for future communication with the help of an authentication server. They also demonstrated that their scheme is provably secure in a formal model. However, in this letter, we will show that Chien et al.’s protocol is vulnerable to the off-line password guessing attack. To overcome the weakness, we also propose an efficient countermeasure. Keywords-Password-based; Authenticated key exchange; Gateway; Off-line password guessing attack