Provably Authenticated Group Diffie-Hellman Key Exchange - The Dynamic Case

Dynamic group Diffie-Hellman protocols for Authenticated Key Exchange (AKE) are designed to work in a scenario in which the group membership is not known in advance but where parties may join and may also leave the multicast group at any given time. While several schemes have been proposed to deal with this scenario no formal treatment for this cryptographic problem has ever been suggested. In this paper, we define a security model for this problem and use it to precisely define Authenticated Key Exchange (AKE) with “implicit” authentication as the fundamental goal, and the entity-authentication goal as well. We then define in this model the execution of a protocol modified from a dynamic group Diffie-Hellman scheme offered in the litterature and prove its security.