Gateway-Oriented Password-Authenticated Key Exchange Protocol with Stronger Security

A gateway-oriented password-based authenticated key exchange (GPAKE) is a three-party protocol, which allows a client and a gateway to establish a common session key with the help of an authentication server. To date, most of the published GPAKE protocols have been subjected to undetectable on-line dictionary attacks. The security models for GPAKE are not strong enough to capture such attacks. In this paper, we define a new security model for GPAKE, which is stronger than previous models and captures desirable security requirement of GPAKE. We also propose an efficient GPAKE protocol and prove its security under the DDH assumption in our model. Our scheme assumes no preestablished secure channels between the gateways and the server unlike previous schemes, but just authenticated channels between them. Compared with related schemes, our protocol achieves both higher efficiency and stronger security.