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With the growth of internet, many network applications are relied on group communication model. To provide confidentiality for the communication between group members, a secret key called group key is used. Since the group is dynamic, whenever there is a membership change (join/leave), group key is changed (rekeying) to provide forward and backward confidentiality. The hierarchical key-tree approach is widely used to achieve logarithmic costs for changing the key. Along with group key, key-tree also comprises of other set of keys called auxiliary keys which must also be changed as a part of rekeying. Key-tree based schemes involve a trusted entity called key server which performs rekeying operations. The load on the key server is increased with the increase in membership change (specifically with leave event). In this paper, we propose a scheme to reduce the load on the key server from O(mlogmn) to O(m) for a group of n users with the degree of the tree being m. The paper also addresses handling membership changes at regular intervals called batch rekeying, which reduces the rekeying complexity.
Date of Conference: 14-17 Dec. 2008