[Resource Topic] 2025/816: Randomized vs. Deterministic? Practical Randomized Synchronous BFT in Expected Constant Time

Welcome to the resource topic for 2025/816

Title:
Randomized vs. Deterministic? Practical Randomized Synchronous BFT in Expected Constant Time

Authors: Xufeng Zhang, Baohan Huang, Sisi Duan, Haibin Zhang

Abstract:

Most practical synchronous Byzantine fault-tolerant (BFT) protocols, such as Sync HotStuff (S&P 2020), follow the convention of partially synchronous BFT and adopt a deterministic design. Indeed, while these protocols achieve O(n) time complexity, they exhibit impressive performance in failure-free scenarios.

This paper challenges this conventional wisdom, showing that a randomized paradigm terminating in expected O(1) time may well outperform prior ones even in the failure-free scenarios. Our framework reduces synchronous BFT to a new primitive called multi-valued Byzantine agreement with strong external validity (MBA-SEV). Inspired by the external validity property of multi-valued validated Byzantine agreement (MVBA), the additional validity properties allow us to build a BFT protocol where replicas agree on the hashes of the blocks. Our instantiation of the paradigm, Sonic, achieves O(n) amortized message complexity per block proposal, expected O(1) time, and enables a fast path of only two communication step.

Our evaluation results using up to 91 instances on Amazon EC2 show that the peak throughput of Sonic and P-Sonic (a pipelining variant of Sonic) is 2.24x-14.52x and 3.08x-24.25x that of Sync HotStuff, respectively.

ePrint: https://eprint.iacr.org/2025/816

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