Beluga: Block Synchronization for BFT Consensus Protocols

TL;DR

Beluga introduces a block synchronizer abstraction for BFT consensus protocols, enhancing efficiency and security, demonstrated by its integration into the Sui blockchain, which improves performance and resilience under attack.

Contribution

It proposes a novel block synchronizer concept for BFT protocols, providing a resource-aware, efficient, and attack-resilient block exchange mechanism.

Findings

Achieves optimal latency in normal conditions

Provides up to 3x higher throughput under attack

Reduces latency by 25x compared to prior designs

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.