Thresh-Hold: Assessment of Threshold Cryptography in Leader-Based Consensus

Byzantine fault tolerant (BFT) systems can be constructed, using the state machine replication (SMR) approach. The usage of threshold cryptography has been widely proposed to confront performance and scalability challenges. We extend the focus on BLS signatures to ECDSA and Schnorr-based schemes and study their impact on BFT-SMR systems. We analyze their suitability for BFT-SMR and study the complexity of four practical, derived schemes. We implement these schemes for the seminal, leader-based HotStuff protocol. Finally, we experimentally quantify both performance impact and replica load under varying threshold schemes and parameters. Architectural constraints limit the applicability of threshold schemes to BFT-SMR. While BLS is the most compatible of the studied schemes, it incurs a significant base cost. We observe that for smaller deployments this increased base cost outweighs the theoretical scaling and performance benefits. Using optimizations such as command batching results in comparable throughput over all studied schemes, albeit with significant latency differences. Our results suggest, that both leader and client are potential bandwidth bottlenecks, already for relatively small payload sizes.