Automatic Verification and Discovery of Byzantine Consensus Protocols

Model-checking of asynchronous distributed protocols is challenging because of the large size of the state and solution spaces. This paper tackles this problem in the context of low-latency Byzantine Consensus protocols. It reduces the state space by focusing on the latency-determining first round only, ignoring the order of messages in this round, and distinguishing between state-modifying actions and state-preserving predicates. In addition, the monotonicity of the predicates and verified properties allows one to use a Tarski-style fixpoint algorithm, which results in an exponential verification speed-up. This model checker has been applied to scan the space of possible Consensus algorithms in order to discover new ones. The search automatically discovered not only many familiar patterns but also several interesting improvements to known algorithms. Due to its speed and reliability, automatic protocol design is an attractive paradigm, especially in the notoriously difficult Byzantine case.