Algorithms for dynamic multicast key distribution

We study the problem of multicast key distribution for group security. Secure group communication systems typically rely on a group key, which is a secret shared among the members of the group. This key is used to provide privacy by encrypting all group communications. Because groups can be large and highly dynamic, it becomes necessary to change the group key in a scalable and secure fashion when members join and leave the group. We present a series of algorithms for solving this problem based on key trees. The algorithms attempt to minimize the worst-case communication cost of updates by maintaining balanced key tree structures. We focus on the trade-off between the communication cost because of the structure of the tree and that due to the overhead of restructuring the tree to maintain its balanced structure. The algorithms are analyzed for worst-case tree structure bounds and evaluated empirically via simulations.