Group authentication scheme based on zero-knowledge proof

In this paper, we address the problem of mutual authentication in user groups in decentralized messaging systems without trusted third party. We propose a mutual authentication algorithm for groups using zero-knowledge proof. Using the algorithm, which is based on trust chains existing in decentralized network, users are able to authenticate each other without establishing a shared secret over side channel. The proposed algorithm is based on Democratic Group Signature protocol (DGS) and Communication-Computation Efficient Group Key algorithm for large and dynamic groups (CCEGK). We have performed security analysis of the proposed mutual authentication scheme against several attacks including Sybil attack and have made complexity estimation for the algorithm. The algorithm is implemented in an experimental P2P group messaging application, and using this implementation we estimate overhead of the authentication scheme and convergence time for several initial configurations of user groups and trust chains.