Efficient secure multicast with well-populated multicast key trees

Secure group communications is the basis for many recent multimedia and Web technologies. In order to maintain secure and efficient communications within a dynamic group, it is essential that the generation and management of group key(s) be secure and efficient with realtime response. Typically, a logical key hierarchy is used for distribution of group keys to users so that whenever users leave or join the group, new keys are generated and distributed using the key hierarchy. In this paper, we propose well-populated multicast key tree (WPMKT), an efficient technique to handle group dynamics in the key tree and maintain the tree balanced with minimal cost. In WPKT, subtrees are swapped in a way that keeps the key tree balanced and well populated. A t the same time, rekeying overhead due to reorganization is kept at a minimum. Another advantage of WPKT is that rebalancing has no effect on the internal key structure of the swapped subtrees. Results from simulation studies show that under random user deletion, our approach achieves one order of magnitude in overhead less than existing approaches. Under clustered sequential user deletion, our approach achieves almost a linear growth with tree size under individual rebalancing. For periodic rebalancing, we achieved almost half the overhead introduced by other approaches.