Icarus: Achieving Performant Asynchronous BFT with Only Optimistic Paths
Xiaohai Dai
Network and Distributed System Security (NDSS) Symposium 2026 · Day 3 · Applied Cryptography
**Byzantine Fault Tolerant (BFT) consensus protocols** are foundational to distributed systems that must remain correct even when some nodes behave maliciously. Asynchronous BFT protocols offer the strongest robustness guarantees by making no timing assumptions about the network, but they traditionally suffer from low efficiency compared to partially synchronous alternatives. The current approach to improving asynchronous BFT efficiency uses a **dual-path paradigm**: an optimistic path leveraging a faster partially synchronous protocol, with a **pessimistic fallback path** using a complex asynchronous protocol like **MVBA (Multi-Value Byzantine Agreement)**. This talk presents **Icarus**, which eliminates the pessimistic path entirely by introducing a new paradigm that runs **only optimistic paths**. When one optimistic path fails, the system switches to another optimistic path rather than falling back to a complex pessimistic protocol. Evaluated on AWS across five global regions, Icarus achieves the **lowest latency** and **highest throughput** compared to existing dual-path protocols (DTO, ParBFT), purely asynchronous protocols (SMVBA, FIN), and DAG-based protocols (Tusk).
AI review
A consensus protocol optimization that eliminates the pessimistic path in asynchronous BFT by switching between optimistic paths. Pure distributed systems engineering with zero security content -- no attacks, no vulnerabilities, no defensive insights.