Time-Free Authenticated Byzantine Consensus

This paper presents a simple protocol that solves the authenticated Byzantine Consensus problem in asynchronous distributed systems. To circumvent the FLP impossibility result in a deterministic way, synchrony assumptions should be added. In the context of Byzantine failures for systems where at most t processes may exhibit a Byzantine behavior and where not all the system is assumed eventually synchronous, Moumen et al. provide the main result. They assume at least one correct process, called 2t-bisource, connected with 2t privileged neighbors with eventually timely outgoing and incoming links. The present paper shows that a deterministic solution for the authenticated byzantine consensus problem is possible if the system model satisfies an additional assumption that does not rely on physical time but on the pattern of messages that are exchanged. The basic message exchange between processes is the query-response mechanism. To solve the Consensus problem, we assume a correct process p, called 2t-winning process, and a set Q of 2t processes such that, eventually, for each query issued by p, any process q of Q receives a response from p among the (n - t) first responses to that query. The processes in the set Q can exhibit a Byzantine behavior and this set may change over time. Whereas many time-free solutions have been designed for the consensus problem in the crash model, this is, to our knowledge, the first time-free deterministic solution to the Byzantine consensus problem.