VLSM: Validating Labelled State Transition and Message Production Systems
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In this paper we introduce the notion of a validating labelled state transition and message production system (VLSM), a tool for formal analysis and specification of faulty distributed systems. We give theories of VLSM composition, state equivocation, message equivocation, and validators. Then we show that the traces of equivocation-limited compositions of validators are precisely the traces of honest components in the context of limited Byzantine faults in an asynchronous network without a guarantee of eventual message arrival. This result shows that the validation strategies of honest nodes can restrict the effect that Byzantine nodes have on them enough that we can express all of their possible faulty traces in terms of equivocation over valid transitions, circumventing the need for Byzantine fault analysis altogether. Our definitions and results have been formalised and machine-checked in the Coq proof assistant.
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