Efficient, Authenticated, and Fault-Tolerant Key Agreement for Dynamic Peer Groups

We present an efficient authenticated and fault-tolerant protocol (AFTD) for tree-based key agreement. Our approach is driven by the insight that when a Diffie-Hellman blinded key is updated, in a tree-based method, it suffices to send the update to a small subset of the group, instead of entire group, as current methods require. Our scheme distributes each updated public key to a relatively small subgroup, called its trust set, greatly improving performance. Moreover, we use a threshold secret sharing method to distribute the function of the trusted authority across trust sets, thereby guaranteeing key authentication, enhancing fault-tolerance, and protecting our protocol from impersonation attacks. Our performance analysis suggests that our scheme significantly reduces the communication overhead and storage requirement.