Holistic Verification of Blockchain Consensus

International audienceBlockchain has recently attracted the attention of the industry due, in part, to its ability to automate asset transfers. It requires distributed participants to reach a consensus on a block despite the presence of malicious (a.k.a. Byzantine) participants. Malicious participants exploit regularly weaknesses of these blockchain consensus algorithms, with sometimes devastating consequences. In fact, these weaknesses are quite common and are well illustrated by the flaws in various blockchain consensus algorithms. Paradoxically, until now, no blockchain consensus has been holistically verified. In this paper, we remedy this paradox by model checking for the first time a blockchain consensus used in industry. We propose a holistic approach to verify the consensus algorithm of the Red Belly Blockchain, for any number n of processes and any number f < n/3 of Byzantine processes. We decompose directly the algorithm pseudocode in two parts-an inner broadcast algorithm and an outer decision algorithm-each modelled as a threshold automaton, and we formalize their expected properties in linear-time temporal logic. We then automatically check the inner broadcasting algorithm, under a carefully identified fairness assumption. For the verification of the outer algorithm, we simplify the model of the inner algorithm by relying on its proven properties. Doing so, we formally verify, for any parameter, not only the safety properties of the Red Belly Blockchain consensus but also its liveness in less than 70 seconds