Brief Note: Fast Authenticated Byzantine Consensus

Byzantine fault-tolerant (BFT) state machine replication (SMR) has been studied for over 30 years. Recently it has received more attention due to its application in permissioned blockchain systems. A sequence of research efforts focuses on improving the commit latency of the SMR protocol in the common good case, including PBFT [5] with 3-round latency and n ≥ 3f + 1 and FaB [11] with 2-round latency and n ≥ 5f + 1. In this paper, we propose an authenticated protocol that solves 2-round BFT SMR with only n ≥ 5f − 1 replicas, which refutes the optimal resiliency claim made in FaB for needing n ≥ 5f + 1 for 2-round PBFT-style BFT protocols. For the special case when f = 1, our protocol needs only 4 replicas, and strictly improves PBFT by reducing the latency by one round (even when one backup is faulty).