Many emerging applications are based on group communication model and many group communications Uke multimedia distribution and miUtary applications require a security infrastrocture that provides multiple levels of access control for group members in which group members are divided into a number of subgroups and placed at ditTerent privilege levels based on certain criteria and a member at higher level must be capable of accessing communication in its own level as well as its descendant lower levels and converse is not true.Two key management schemes have been developed to provide hierarchical access control: first method is key-based and the second one is share-based. Constrocting a hierarchical group communication model based on secret shares is more flexible rather than using keys. In this paper we use share-based key management scheme and propose to reduce the storage at higher level users as compared to the scheme proposed by Dexter et al. by reusing a part of the pre-positioned information as common for all the layers in the system. We compare the storage and encryption cost of our scheme with the scheme proposed by Dexter et al. We also address periodic group rekeying.

SUMMARYNumerous emerging applications, such as teleconferencing, board meetings, pay-per-view and scientifi c discussions, rely on a secure group communication model. Scalable group rekeying is an important issue in the secure group communication model as the nature of the group is dynamic. The number of encryptions performed and rekey messages constructed should be minimized to carry out updating of the group key, and secure delivery of the group key should be carried out in an effi cient manner. In this paper, we propose a new scheme to manage the secure group using the binomial key tree approach. In this scheme, the number of encryptions performed and rekey messages constructed during membership change are fewer compared to the scheme proposed by Wong and others. Further, it is not required to balance the tree after each membership change. We show that, for a large group, the average encryption cost and rekey message cost are independent of the size of the group for join operation and logarithmic in size of the group for leave operation. Hence our scheme is scalable.

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