Beluga: Block Synchronization for BFT Consensus Protocols

2025-11-19

AI Summary

Modern high-throughput BFT consensus protocols lack efficient and robust block exchange mechanisms, rendering them vulnerable to targeted attacks—such as redundant pull-based fetching—and causing severe performance degradation under asynchronous network conditions. Method: This paper introduces the “block synchronizer” abstraction, formally defining and implementing a resource-aware, incremental block acquisition mechanism. It identifies and mitigates a novel bandwidth-exhausting redundant pull attack, derives theoretical bounds on recovery cost under failures and adversarial conditions, and proposes a modular, scarcity-aware hybrid push-pull dissemination design integrated into the Mysticeti consensus protocol. Results: Deployed on the Sui mainnet, the system achieves optimal latency in optimistic scenarios and, under attack, delivers a 3× throughput improvement and a 25× reduction in latency compared to baseline approaches.

Technology Category

• Multiagent Systems: Mechanism Design
• Search and Optimization: Distributed Search
• Data Mining & Knowledge Management: Representing, Reasoning, and Using Provenance, Trust

Application Category

• Security and Privacy: Blockchains and distributed ledgers
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

Abstract

Modern high-throughput BFT consensus protocols use streamlined push-pull mechanisms to disseminate blocks and keep happy-path performance optimal. Yet state-of-the-art designs lack a principled and efficient way to exchange blocks, which leaves them open to targeted attacks and performance collapse under network asynchrony. This work introduces the concept of a block synchronizer, a simple abstraction that drives incremental block retrieval and enforces resource-aware exchange. Its interface and role fit cleanly inside a modern BFT consensus stack. We also uncover a new attack, where an adversary steers honest validators into redundant, uncoordinated pulls that exhaust bandwidth and stall progress. Beluga is a modular and scarcity-aware instantiation of the block synchronizer. It achieves optimal common-case latency while bounding the cost of recovery under faults and adversarial behavior. We integrate Beluga into Mysticeti, the consensus core of the Sui blockchain, and show on a geo-distributed AWS deployment that Beluga sustains optimal performance in the optimistic path and, under attack, delivers up to 3x higher throughput and 25x lower latency than prior designs. The Sui blockchain adopted Beluga in production.

Problem

• Lack efficient block exchange method in BFT protocols
• Vulnerability to targeted attacks under network asynchrony
• Bandwidth exhaustion from uncoordinated redundant block pulls

Innovation

• Block synchronizer abstraction for incremental retrieval
• Resource-aware exchange enforcing bandwidth limits
• Modular scarcity-aware design bounding recovery costs