Mir-BFT: High-Throughput BFT for Blockchains

This paper presents Mir-BFT (or, simply, Mir), a robust asynchronous Byzantine fault-tolerant (BFT) total order broadcast protocol aimed at maximizing throughput on wide-area networks (WANs) with up to 100 nodes. This deployment setting is highly relevant to many permissioned and Proof-of-Stake permissionless blockchains. Mir achieves unprecedented throughput on WANs without sacrificing latency, robustness to malicious behavior, or even performance in clusters. To achieve this, Mir is the first BFT protocol that allows a set of leaders to propose request batches independently, in parallel, while preventing request duplication performance attacks through a rotating assignment of a partitioned request hash space to leaders. We also propose several optimizations to Mir that boost the throughput even further, including partial replication through a novel abstraction we call light total order (LTO) broadcast. Perhaps most importantly, Mir relies on proven BFT protocol constructs, which is fundamental to Mir provability and correctness. Specifically, Mir is a generalization of the celebrated and scrutinized PBFT protocol. While Mir follows PBFT ``safety-wise'', it introduces substantial changes with respect to PBFT liveness (i.e., leader election), which help it become the highest throughput BFT protocol on WANs with up to 100 nodes to date, reaching more than 23000 Bitcoin-sized tps.