Simple-IT achieves low-latency BFT consensus without digital signatures

As quantum computing advances, most Byzantine fault-tolerant (BFT) consensus protocols face obsolescence because they depend on public-key signature schemes like Ed25519 and BLS12-381 that quantum computers could break. While switching to post-quantum secure signatures is possible, those schemes are computationally expensive. An alternative is signature-free BFT, which uses only cheap, post-quantum secure authenticated channels. However, prior signature-free designs were either too complex to implement or could not match the low latency of signature-based protocols. Enter Simple-IT, introduced by Qianyu Yu, Juan Villacis, Giuliano Losa, Zhuolun Xiang, and Xuechao Wang in a June 2026 arXiv paper.

Simple-IT is a leader-based BFT protocol that achieves a theoretical latency of just 4 message delays (with an optimistic path of only 3 delays), one more than the theoretical optimum. Its key innovation is simplicity: the protocol is straightforward enough to implement practically and to support optimizations like speculative pipelining. In geo-distributed experiments, Simple-IT demonstrated both throughput and latency competitive with state-of-the-art quantum-vulnerable protocols. This makes it a strong candidate for securing distributed ledgers and other consensus systems against quantum threats without sacrificing performance or introducing costly cryptography.