A modified CLIQUES key agreement protocol for secure multicast

In a secured multicast application, members may join or leave frequently. Hence, key management is one of the most challenging problems. A practical and scalable key management requires high security features, efficient key distribution, low key-storage cost, and small processing overhead. CLIQUES (1-5) scheme was proposed to handle contributory key agreement. It extends the two-party Diffie-Hellman (6) algorithm to allow a group of members to "agree" upon a symmetric group key. Among the existing key management approaches, CLIQUES has the lowest cost in establishing the common session key. It also imposes less processing overhead in the user machine. The main drawback of CLIQUES is that a large number of re-key messages have to be exchanged among members when there is a membership change. The number of messages exchanged is proportional to the size of the membership. Consequently, CLIQUES is not very scalable and cannot support large group of members. In this thesis, we proposed a Static CLIQUES, in which, a static group controller is introduced to reduce the complexity of status synchronization process within the group when there is a membership change. The number of keys stored in each member is smaller than that of the original CLIQUES. In addition, the use of static group controller provides member privacy protection since individual member does not have direct contact with other members. We also proposed a hierarchical CLIQUES structure to support a large number of members by sub-grouping them logically into a hierarchical key tree. It is more scalable than dynamic CLIQUES. The size of re-key message being distributed is found to be comparable with hierarchical key tree approach (7-11).