In this thesis, we propose an adaptive multicast key management scheme for secure group communications. In a secure communication session, group members could dynamically join and leave the group. Therefore, a multicast key management scheme is required to ensure that only legitimate users will continue to receive the latest information. In the literature, star-based key management schemes and tree-based key management schemes were proposed for secure group communications. In this thesis, we propose a novel canonical-tree-based key management scheme. We evaluate the average rekeying costs of the canonical-tree-based scheme as well as two well-known key management schemes. We find that the leaving probability of group members dominates the relative performance between the star-based scheme and the tree-based scheme. Based on the above observations, we propose an adaptive key management scheme that is superior to both the star-based scheme and the tree-based scheme in a dynamic environment.

We propose a balanced tree structure overlay on a peer-to-peer network capable of supporting both exact queries and range queries efficiently. In spite of the tree structure causing distinctions to be made between nodes at different levels in the tree, we show that the load at each node is approximately equal. In spite of the tree structure providing precisely one path between any pair of nodes, we show that sideways routing tables maintained at each node provide sufficient fault tolerance to permit efficient repair. Specifically, in a network with N nodes, we guarantee that both exact queries and range queries can be answered in O(logN) steps and also that update operations (to both data and network) have an amortized cost of O(logN). An experimental assessment validates the practicality of our proposal. / Singapore-MIT Alliance (SMA)