International Association
for Cryptologic Research

State-of-the-art asynchronous Byzantine Fault Tolerance (BFT) protocols integrate a partially-synchronous optimistic path. The holy grail in this paradigm is to match the performance of a partially-synchronous protocol in favorable situations and match the performance of a purely asynchronous protocol in unfavorable situations. Several prior works have made progress toward this goal by matching the efficiency of a partially-synchronous protocol in favorable conditions. However, their performance compared to purely asynchronous protocols is reduced when network conditions are unfavorable. To address these shortcomings, a recent work, Abraxas (CCS'23), presents the first optimistic asynchronous BFT protocol that retains stable throughput in all situations. However, Abraxas still incurs very high worst-case latency in unfavorable situations because it is slow at detecting the failure of its optimistic path. Another recent work, ParBFT (CCS'23) guarantees good latency in all situations, but suffers from reduced throughput in unfavorable situations due to its use of extra Asynchronous Binary Agreement (ABA) instances.

To approach our holy grail, we propose Ipotane. Ipotane achieves performance comparable to partially-synchronous protocols in favorable situations, and attains performance on par with purely asynchronous protocols in unfavorable situations---in both throughput and latency. This is accomplished by our newly introduced primitive Dual-functional Byzantine Agreement (DBA), which packs the functions of (biased) ABA and Validated Asynchronous Byzantine Agreement (VABA). In the context of Ipotane, it promptly detects the optimistic path's failure and, at the same time, generates blocks on the pessimistic path with little extra work. We conduct extensive experiments to demonstrate that Ipotane achieves high throughput and low latency in all situations.