Group Key Exchange Secure against Strong Corruptions

When a set of users run a group key exchange (GKE) protocol, they usually extract the key from some auxiliary (ephemeral) secret information generated during the execution itself. Strong corruptions are attacks by which an adversary can reveal these ephemeral secrets. Undoubtedly, their security impact is serious, and thus specifying appropriate security requirements and designing secure GKE protocols appears an interesting yet challenging task — the aim of our paper. More precisely, we define security goals for GKE protocols in the presence of such powerful adversaries and propose a protocol immune to strong corruption attacks. Our model in particular includes the case of misbehaving participants, for appropriate security goals, e.g., mutual authentication, key confirmation, contributiveness and keyreplication resilience. The proposed protocol proceeds in a constant number of rounds.