Signature-Free Broadcast-Based Intrusion Tolerance

International audienceProviding application processes with strong agreement guarantees despite failures is a fundamental problem of fault-tolerant distributed computing. Correct processes have not to be ``polluted'' by the erroneous behavior of faulty processes. This paper considers the consensus agreement problem in a setting where some processes can behave arbitrarily (Byzantine behavior). In such a context it is possible that Byzantine processes collude to direct the correct processes to decide on a ``bad'' value (a value proposed only by faulty processes). The paper has several contributions. It presents a family of consensus algorithms in which no bad value is ever decided by correct processes. These processes always decide a value they have proposed or a default value "bottom". These algorithms are called intrusion-free consensus algorithms. To that end, each consensus algorithm is based on an appropriate underlying broadcast algorithm. One of these abstractions, called "validated broadcast" is new and allows the design of a resilience-optimal consensus algorithm (i.e., it copes with up to tCet article présente un famille de protocoles de diffusion offrant de plus en plus de garanties dans un système réparti asynchrone où une partie (au plus t) des n processus du système peuvent exhiber un comportement byzantin. Cet article montre quelles sont les conditions exigées par chaque primitive pour qu'elle soit implémentable et de plus donne le coût de chacune d'elles en termes de nombre d'étapes de communication nécessitées et de nombres de messages échangés