Efficient Collaborative Key Management Protocols for Secure Autonomous Group Communication

This paper introduces a new family of protocols addressing collaborative group key agreement for secure group communication in autonomous groups. I present three protocols with varying degrees of security and efciency. The rst protocol provides a non-authenticated key agreement and is suitable for applications with low security requirements. The second and third protocols add a DiÆe-Hellman-based authenticated key agreement to provide collaborative authentication. In particular, the third protocol uses G unther's concept of implicitlycerti ed public keys to achieve higher eÆciency. A major advantage of the protocols is that they allow eÆcient \join" and \leave" operations, while preserving perfect forward and backward secrecy. These protocols improve previously proposed schemes in the following ways: rst, they can be used for autonomous group key agreement, where no central server is necessary and no member has a special role. Also, the complexity is drastically reduced: compared to best currently used techniques, the number of rounds for the initial key agreement are reduced from n to log(n), and the bandwidth requirements are reduced from O(n) to O(n), where n is the number of members. In addition, I present new primitives that enforce rights management policies in the group (such as sender authorization).