A New Security Model for Cross-Realm C2C-PAKE Protocol ∗

Abstract. Cross realm client-to-client password authenticated key exchange (C2C-PAKE) schemes are designed to enable two clients in different realms to agree on a common session key using different passwords. In 2006, Yin-Bao presented the first provably secure cross-realm C2C-PAKE, which security is proven rigorously within a formally defined security model and based on the hardness of some computationally intractable assumptions. However, soon after, Phan et al. pointed out that the Yin-Bao scheme was flawed. In this paper, we first analyze the necessary security attributes in the cross-realm C2C-PAKE scenario, and then a new security model for cross-realm C2C-PAKE is given. Analogous to the general construction of 3PAKE protocol for single server C2C-PAKE setting, we give a general construction of cross-realm C2C-PAKE protocol, which security is proved in the new security model. Key word: Password-authenticated key exchange, cross realm, client-to-client, provably secure, security model.