Paper 2022/1448

Towards Practical Sleepy BFT

Abstract

Bitcoin's longest-chain protocol pioneered consensus under dynamic participation, also known as sleepy consensus, where nodes do not need to be permanently active. However, existing solutions for sleepy consensus still face two major issues, which we address in this work. First, existing sleepy consensus protocols have high latency (either asymptotically or concretely). We tackle this problem and achieve $4\Delta$ latency ($\Delta$ is the bound on network delay) in the best case, which is comparable to classic BFT protocols without dynamic participation support. Second, existing protocols have to assume that the set of corrupt participants remains fixed throughout the lifetime of the protocol due to a problem we call \emph{costless simulation}. We resolve this problem and support growing participation of corrupt nodes. Our new protocol also offers several other important advantages, including support for arbitrary fluctuation of honest participation as well as an efficient recovery mechanism for new active nodes.

Note: The materials in the appendix appeared in a previous version of this work under the title ``Byzantine Consensus under Fully Fluctuating Participation'' and presented protocols with 1/3 (instead of 1/2) fault tolerance.