An efficient distributed group key management algorithm

A key agreement protocol is an important part of a secure group communication system (SGCS) which provides secure message passing services to its members. Among the various distributed key agreement protocols proposed in the literature, the tree-based group Diffie-Hellman (TGDH) protocol is the most efficient in terms of the number of keys that need to be maintained at each member and distribution of DH exponentiation operations among group members. In TGDH, on a group change, the group members need to perform between one and O(log₂n) exponentiation operations serially. Also, the messages that are passed during group key agreement must be authenticated using digital signatures. In this paper, we propose a key agreement protocol which minimizes the number of exponentiation operations at each member. The member join operation requires only three members to perform one or two exponentiation operations each while the member leave operation requires only two or five group members to perform one or two exponentiation operations each. This is achieved at the cost of O(log₂n) causal messages per member leave operation.