Provably Authenticated Group Diie-hellman Key Exchange the Dynamic Case (extended Abstract)

Dynamic group Diie-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 deene a security model for this problem and use it to precisely deene Authenticated Key Exchange (AKE) with implicitt authentica-tion as the fundamental goal, and the entity-authentication goal as well. We then deene in this model the execution of a protocol modiied from a dynamic group Diie-Hellman scheme ooered in the literature and prove its security.