An information-theoretic approach for design and analysis of rooted-tree-based multicast key management schemes

Recent literature presents several rooted tree based member deletion/revocation schemes [20, 21, 22, 24, 4, 5] trying to simultaneously minimize the key storage while providing e cient member deletion/revocation. Many of these approaches have di erent solutions and provide di erent values for the number of keys to be stored and distributed. In this paper, we show that many of these papers can be systematically studied using basic concepts from information theory. In particular, we show that the entropy of member revocation event, plays a major role in de ning the key allocation requirements. We then relate the entropy of member revocation event to provide bounds on the key length. We also show that the optimal Hu man coding strategy used in [22, 24] leads to security weakness. A method for generating Key management schemes with varying degrees of member collusion is also presented in this paper.