Minimization of rekeying cost for contributory group communications

While contributory group key agreement is a promising solution to achieve access control in collaborative and dynamic group applications, the existing schemes have not achieved the performance lower bound in terms of rekeying overhead. In this paper we introduce a contributory group key agreement that achieves the performance lower bound by utilizing a novel logical key tree structure, called PFMH, and the concept of phantom user position. In particular, the proposed scheme only needs O(1) rounds of two-party Diffie-Hellman upon any single user join event and O(log n) rounds of two-party Diffie-Hellman upon any single user leave event. Both theoretical bound analysis and simulation studies show that the proposed scheme achieves much lower rekeying cost than the existing tree-based contributory group key agreement schemes.