Fall 2019

LibraBFTv2: Optimistically-linear BFT Consensus with Concrete Latency Bounds

Thursday, October 24th, 2019 3:00 pm3:30 pm

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Mathieu Baudet (Facebook/Calibra)

LibraBFT is a refinement of the HotStuff protocol that makes explicit the mechanisms used to achieve round synchronization between nodes. In this talk, I will present the second version of the protocol, LibraBFTv2. In the optimistic case (aka “happy path”), LibraBFTv2 reduces the overhead of round synchronization to a single message per node per round. The initial version of LibraBFT relied on probabilistic gossip to ensure uniform propagation of quorum certificates. In contrast, LibraBFTv2 achieves round synchronization without using probabilistic gossip. First, the new protocol introduces a new type of failsafe mechanisms that regularly pull missing data in case no progress is made. Second, LibraBFTv2 simplifies the constraints on block proposals. The new constraints ensure that an honest leader can always propose a block and force round synchronization soon after the first honest node enters her round. The proof of liveness of LibraBFTv2 shows that the concrete latency bounds under Byzantine (worst-case) scenarios are comparable to LibraBFTv1, while the number of messages is now linear in the optimistic case.