Secure multicast in dynamic environments

A secure multicast framework should only allow authorized members of a group to decrypt received messages; usually, one “group key” is shared by all approved members. However, this raises the problem of “one affects all”, whereby the actions of one member affect the whole group. Many researchers have solved the problem by dividing a group into several subgroups, but most current solutions require key distribution centers to coordinate secure data communications between subgroups. We believe this is a constraint on network scalability. In this paper, we propose a novel framework to solve key management problems in multicast networks. Our contribution is threefold: (1) We exploit the ElGamal cryptosystem and propose a technique of key composition. (2) Using key composition with proxy cryptography, the key distribution centers used in secure multicast frameworks are eliminated. (3) For key composition, the framework is designed to resist node failures and support topology reconstruction, which makes it suitable for dynamic network environments. Without reducing the security or performance of proxy cryptography, we successfully eliminate the need for key distribution centers. Our analysis shows that the proposed framework is secure, and comparison with other similar frameworks demonstrates that it is efficient in terms of time and space complexity. In addition, the costs of most protocol operations are bounded by constants, regardless of a group's size and the number of branches of transit nodes.