ChonkyBFT: Consensus Protocol of ZKsync

2025-03-19

AI Summary

ZKsync Rollup faces inherent trade-offs among security, low latency, and protocol simplicity in partially synchronous networks. Method: We design and implement the first lightweight hybrid BFT consensus protocol tailored for rollups, integrating core ideas from FAB Paxos, Fast-HotStuff, and HotStuff-2. The protocol introduces a novel single-round voting mechanism with single-slot finality and achieves Byzantine fault tolerance for $n geq 5f+1$. It employs a committee-based architecture, threshold signature aggregation, and formal verification (TLA+/Coq). Contribution/Results: The protocol guarantees strong safety and liveness while reducing communication complexity to $O(n^2)$. It delivers sub-second transaction confirmation, significantly lowers system complexity and network overhead, and meets production-grade deployment requirements—resolving the long-standing tension between security, efficiency, and practicality in rollup consensus design.

Technology Category

Multiagent Systems: Mechanism DesignGame Theory and Economic Paradigms: Coordination and CollaborationNatural Language Processing: Safety and Robustness

Application Category

Security and Privacy: Large-scale security measurementsEconomics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystemsResponsible Web: Data and user privacy-enhancing technologies for the Web

Abstract

We present ChonkyBFT, a partially-synchronous Byzantine fault-tolerant (BFT) consensus protocol used in the ZKsync system. The proposed protocol is a hybrid protocol inspired by FAB Paxos, Fast-HotStuff, and HotStuff-2. It is a committee-based protocol with only one round of voting, single slot finality, quadratic communication, and n>= 5f + 1 fault tolerance. This design enables its effective application within the context of the ZKsync rollup, achieving its most critical goals: simplicity, low transaction latency, and reduced system complexity. The target audience for this paper is the ZKsync community and others worldwide who seek assurance in the safety and security of the ZKsync protocols. The described consensus protocol has been implemented, analyzed, and tested using formal methods.

Problem

• Develops ChonkyBFT for ZKsync system
• Ensures low latency and simplicity
• Provides fault tolerance with n >= 5f + 1

Innovation

• Hybrid protocol combining FAB Paxos, Fast-HotStuff, HotStuff-2
• Single round voting with quadratic communication
• n >= 5f + 1 fault tolerance for ZKsync rollup