Strengthened Fault Tolerance in Byzantine Fault Tolerant Replication

TL;DR

This paper introduces a strengthened fault tolerance mechanism for Byzantine fault tolerant state machine replication that offers increased resilience during optimistic periods without increasing message complexity.

Contribution

It proposes a novel SFT approach that enhances fault tolerance in BFT SMR under partial synchrony, maintaining linear message complexity and minimal overhead.

Findings

Achieves resilience up to two-thirds Byzantine faults after optimistic periods

Maintains linear message complexity similar to existing BFT protocols

Demonstrates efficiency through implementation in the Diem project

Abstract

Byzantine fault tolerant (BFT) state machine replication (SMR) is an important building block for constructing permissioned blockchain systems. In contrast to Nakamoto Consensus where any block obtains higher assurance as buried deeper in the blockchain, in BFT SMR, any committed block is secure has a fixed resilience threshold. In this paper, we investigate strengthened fault tolerance (SFT) in BFT SMR under partial synchrony, which provides gradually increased resilience guarantees (like Nakamoto Consensus) during an optimistic period when the network is synchronous and the number of Byzantine faults is small. Moreover, the committed blocks can tolerate more than one-third (up to two-thirds) corruptions even after the optimistic period. Compared to the prior best solution Flexible BFT which requires quadratic message complexity, our solution maintains the linear message complexity of state-of-the-art BFT SMR protocols and requires only marginal bookkeeping overhead. We implement our solution over the open-source Diem project, and give experimental results that demonstrate its efficiency under real-world scenarios.