Comments on Gateway-Oriented Password-Based Authenticated Key Exchange Protocol

A gateway-oriented password-based authenticated key exchange (GPAKE) scheme allows a client to establish an authenticated session key with a gateway via the help of an authentication server, where the client has pre-shared a password with the server. The desirable security properties of a GPAKE include session key semantic security, key privacy against the server, and password guessing attacks resistance. This letter shows that both Byun et al.´s schemes failed to commit the security requirements. The improved scheme would be proposed in the extended version.