Scalable balanced batch rekeying for secure group communication

Secure group communication is important for applications such as pay-per-view. Other authors have proposed the key tree approach to distribute a shared group key in a way such that the rekeying cost scales linearly with the logarithm of the group size for a join or depart request. The efficiency of the key tree approach depends critically on whether the key tree remains balanced. Periodic rebalancing can be used to balance the key tree whenever it becomes unbalanced but this adds extra costs to the network. In this paper, we present two Merging Algorithms suitable for batch join events. As the multicast session consists of other events as well, we then show how we can extend our algorithms into existing work to minimise the maximum difference in height without adding extra network costs. Simulation results show our Merging Algorithms not only balance the key tree but their rekeying costs are lower compared to existing algorithms.