Abstract: Based on the security of the discrete logarithm, an FGKA (fast group key agreement) protocol, that fits for small Ad Hoc networks, is presented. It combines contribution information of all members with the secret value selected by the sponsor. To fits for the large Ad Hoc network, the above protocol is extended to the AT-FGKA(Arbitrary Topology-FGKA) protocol which can be adapted to an arbitrary network by using the k-ary tree. Finally, dynamic member maintenance protocols as well as security analysis and efficiency comparison are described, which shows that the former has little communication and computation, and that the latter can reduce communication cost effectively.

Key words: key agreement, group key, key management, Ad Hoc