A Two-Round Group Key Agreement Protocol from RLWE in the Extended GBG Model

Group key agreement (GKA) is an widely used cryptographic tool that allows a group to share a common session key and establish a secure channel within their group. To resist quantum attacks, some GKA protocols are constructed based on lattice problem. However, the known lattice-based GKA protocols doesn't consider the ephemeral key leakage attack. If a user leaks his ephemeral key that used to establish a session key, adversaries may break the security of this session. In this work, we proposed a two-round GKA protocol based on RLWE that achieves the resistance of quantum attack. The proposed GKA protocol also achieves authenticated key exchange (AKE) security under the extended GBG model, which means that it is still secure if the ephemeral keys of users are revealed.