Distributed collaborative key agreement protocols for dynamic peer groups

We consider several distributed collaborative key agreement protocols for dynamic peer groups. This problem has several important characteristics which make it different from traditional secure group communication. They are (1) the distributed nature in which there is no centralized key server, (2) collaborative nature in which the group key is contributory; i.e., each group member will collaboratively contribute its part to the global group key, and (3) the dynamic nature in which existing members can leave the group while new members may join. Instead of performing individual rekey operations, i.e., recomputing the group key after every join or leave request, we consider an interval-based approach of rekeying. In particular, we consider three distributed algorithms for updating the group key: (1) the rebuild algorithm, (2) the batch algorithm, and (3) the queue-batch algorithm. Performance of these distributed algorithms under different settings, such as different join and leave probabilities, is analyzed. We show that these three distributed algorithms significantly outperform the individual rekey algorithm, and that the queue-batch algorithm performs the best among the three distributed algorithms. Moreover the queue-batch algorithm has the intrinsic property of balancing the computation/communication workload such that the dynamic peer group can quickly begin secure group communication. This provides a fundamental understanding about establishing a collaborative group key for a distributed dynamic peer group.

1. Introduction

With the emergence of many group-oriented distributed applications such as multi-player games and tele/video-conferencing, there is a need for security services to provide group-oriented communication privacy and data integrity. To provide this form of group communication privacy, it is important that members of the group can establish a common secret key for encrypting group communication data. For example, consider a group of people in a peer-to-peer ad hoc network having a closed and confidential business meeting. Since they have not previously agreed upon a common secret key, communication between group members is susceptible to eavesdropping. To solve the problem, we need a secure distributed group key agreement protocol such that the group of people can establish the common group key for secure and private communication. Note that this type of key agreement protocols is both distributed and contributory in nature: each member of the group contributes its part to the overall group key.