Forward Security for an Efficient Password-Based Authenticated Key Exchange

A password-based authenticated key exchange (PAKE) protocol in the three-party setting allows two clients com- municating over a public network to agree on a common session key with the help of a server. In the setting the users do not share a password between themselves, but only with the server. In this paper, we propose a new efficient password-based authenticated three-party key ex- change protocol and provide a rigorous conclusion of for- ward security for it in both the random-oracle and the ideal- cipher models under the gap Diffie-Hellman intractability assumption. It is a significant advantage that our proto- col is proved secure in a model that allows the adversary to make adaptive corrupt queries, in contrast to previous solutions.