MonadBFT: Fast, Responsive, Fork-Resistant Streamlined Consensus

Abstract: This paper introduces MonadBFT, a novel Byzantine Fault Tolerant (BFT) consensus protocol designed to significantly enhance both performance and scalability. MonadBFT achieves linear message and authenticator complexity on the happy path, enabling it to improve decentralization. It achieves speculative finality within a single round and is optimistically responsive. The speculative mechanism is refined such that only block equivocation can revert speculative execution, enabling the protocol to ensure accountability for malicious behavior. A notable innovation of MonadBFT is its built-in resistance to a specific form of Maximal Extractable Value (MEV) vulnerability known as tail-forking. Tail-forking occurs when a malicious leader forks away from its predecessor's block, causing that block to be abandoned and depriving the predecessor of rewards. This allows the malicious leader to reorder, steal, or exploit transactions, thereby exacerbating MEV exploitation. MonadBFT effectively mitigates such vulnerabilities, ensuring fairness and integrity in transaction processing. To our knowledge, no other pipelined leader-based BFT consensus protocol combines all these features.