Title: Making BFT Consensus Live

Abstract: Partially synchronous BFT consensus protocols typically structure their execution into a sequence of views, each with a designated leader process. The key to guaranteeing liveness in these protocols is to ensure that all correct processes eventually overlap in a view with a correct leader for long enough to reach a decision. We propose a simple view synchronizer abstraction that encapsulates the corresponding functionality for single-shot BFT consensus protocols, thus simplifying their design. We present a formal specification of a view synchronizer and its implementation under partial synchony, which runs in bounded space despite tolerating message loss during asynchronous periods. We show that our synchronizer specification is strong enough to guarantee liveness for single-shot versions of several well-known BFT consensus protocols, including HotStuff, Tendermint, PBFT and SBFT. We furthermore give precise latency bounds for these protocols when using our synchronizer. By factoring out the functionality of view synchronization we are able to specify and analyze the protocols in a uniform framework, which allows comparing them and highlights trade-offs.

About the Speaker: Alexey Gotsman is an Associate Research Professor at the IMDEA Software Institute in Madrid, Spain. Further details about Alexey can be found here: http://software.imdea.org/~gotsman/

About the Seminar: The COBRA Seminars are weekly seminars hosted by COBRA. The seminars are open to everyone with an interest in blockchain. Further details about COBRA and the weekly seminar can be found here: https://cs.au.dk/research/centers/concordium/activities/cobra-seminars/