Instantiation of Apon et al.'s GKE (PQCrypto 2019) and its vulnerability by key-reuse attack

Abstract

A cryptosystem is used to communicate securely with the intended party on insecure channels. Before using a cryptographic system, two users or group members should perform a key exchange protocol, and then users or members can initiate a cryptographic system. Recently, as the group-based working environment, not two people, increases, the key exchange within a group becomes important. Since Burmester and Desmedt proposed group key exchange protocols in 1994, numerous researches have been conducted. Apon et al. first presented the constant round group key exchange protocol based on the lattice problem. However Apon et al. proposed the key reconciliation mechanism of protocol as general design, rather than specifically designed it. In this paper, we instantiate the Apon et al.’s protocol using the key reconciliation mechanism of NewHope, which is a two-party key exchange protocol, and analyze its correctness and security. Also, we suggest that we should be careful when applying the key reconciliation mechanism through a key-reuse attack.