Consensus in Byzantine asynchronous systems

This paper presents a consensus protocol resilient to Byzantine failures. It uses signed and certified messages and is based on two underlying failure detection modules. The first is a muteness failure detection module of the class ◇M. The second is a reliable Byzantine behaviour detection module. More precisely, the first module detects processes that stop sending messages, while processes experiencing other non-correct behaviours (i.e., Byzantine) are detected by the second module. The protocol is resilient to F faulty processes, F ≤ min(⌊(n - 1)/2⌋, C) (where C is the maximum number of faulty processes that can be tolerated by the underlying certification service). The approach used to design the protocol is new. While usual Byzantine consensus protocols are based on failure detectors to detect processes that stop communicating, none of them use a module to detect their Byzantine behaviour (this detection is not isolated from the protocol and makes it difficult to understand and prove correct). In addition to this modular approach and to a consensus protocol for Byzantine systems, the paper presents a finite state automaton-based implementation of the Byzantine behaviour detection module. Finally, the modular approach followed in this paper can be used to solve other problems in asynchronous systems experiencing Byzantine failures. © 2003 Elsevier B.V. All rights reserved.