Practical and provably-secure multicasting over high-delay networks

This paper considers the problem of authenticated key exchange in a dynamic group in which members join and leave the group in an arbitrary fashion. A group key exchange scheme for such a dynamic group is designed to minimize the cost of the rekeying operations associated with group updates. Although a number of schemes have attempted for many years to address this problem, all provably-secure schemes are inadequate in dealing with a dynamic group where group members are spread across a wide area network; their communication overhead for group rekeying is significant in terms of the number of communication rounds or the number of messages, both of which are recognized as the dominant factors that severely slow down group key exchange over a wide area network. In this paper, we propose an efficient key exchange scheme for this scenario and prove its security against an active adversary under the factoring assumption. The proposed scheme requires only a constant number of rounds while achieving low message complexity.