UC-secure and Contributory Password-Authenticated Group Key Exchange

The contributory property allows participants of group key exchange fairly to engage in the generation of the random session key rather than an entity or some part of members solely to determinate it or force it to lie in an undesired distribution. In this paper, we put forth a password-authenticated group key exchange (GPAKE) in which principals cooperate to agree a strong session key just in possession of a short password. The scheme realizes the optimality of contributory property—full-contributiveness—as long as there is one honest party, the uniform distribution of final session keys can be guaranteed. Moreover, it reaches the security definitions in the well-known universal composability (UC) framework under the random oracle model based on the one-more gap Diffie-Hellman assumption. In particular, our scheme that achieves these results with only two-round messages, has better performances on round complexity in comparison with the existing UC-secure schemes.