191 research outputs found

    Symbolic Bisimulation for Probabilistic Systems

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    International audienceThe paper introduces symbolic bisimulations for a simple probabilistic π-calculus to overcome the infinite branching problem that still exists in checking ground bisimulations between probabilistic systems. Especially the definition of weak (symbolic) bisimulation does not rely on the random capability of adversaries and sug- gests a solution to the open problem on the axiomati- zation for weak bisimulation in the case of unguarded recursion. Furthermore, we present an efficient char- acterization of symbolic bisimulations for the calculus, which allows the ”on-the-fly” instantiation of bound names and dynamic construction of equivalence rela- tions for quantitative evaluation. This directly results in a local decision algorithm that can explore just a minimal portion of the state spaces of probabilistic pro- cesses in question

    PicNIc - Pi-calculus Non-Interference checker

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    PICNIC is a tool for verifying security properties of systems, namely non-interference properties of processes expressed as terms of the pi-calculus with two security levels and declassification primitives. More precisely, it checks whether inserting a process into two different high contexts no information leakage to the low level observers occurs. These properties are decidable over finite control processes, but decidability can be extended by compositionality also to some infinite state processes. Notably, PICNIC has been developed in Fresh OpsilaCaML, a dialect of CaML with native support for binders and fresh/local names; thus, this work can be seen also as a non-trivial case study about the applicability of these new programming languages

    Bisimulator 2.0: An On-the-Fly Equivalence Checker based on Boolean Equation Systems

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    International audienceEquivalence checking is a classical verification method determining if a finite-state concurrent system (protocol) satisfies its desired external behaviour (service) by comparing their underlying labeled transition systems (LTSs) modulo an appropriate equivalence relation. Local (or on-the-fly) equivalence checking explores the synchronous product of the LTSs incrementally, allowing an efficient detection of errors in complex systems. In this paper, we consider the technique based on translating the equivalence checking problem in terms of the local resolution of a boolean equation system (BES). We propose two enhancements of this technique in the case of equivalent LTSs: a new, faster BES encoding of weak equivalence relations, and a new local BES resolution algorithm with a good average complexity. These enhancements were incorporated into the BISIMULATOR 2.0 equivalence checker of the CADP toolbox, and led to significant performance improvements

    Up-To Techniques for Generalized Bisimulation Metrics

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    Bisimulation metrics allow us to compute distances between the behaviors of probabilistic systems. In this paper we present enhancements of the proof method based on bisimulation metrics, by extending the theory of up-to techniques to (pre)metrics on discrete probabilistic concurrent processes. Up-to techniques have proved to be a powerful proof method for showing that two systems are bisimilar, since they make it possible to build (and thereby check) smaller relations in bisimulation proofs. We define soundness conditions for up-to techniques on metrics, and study compatibility properties that allow us to safely compose up-to techniques with each other. As an example, we derive the soundness of the up-to-bisimilarity-metric-and-context technique. The study is carried out for a generalized version of the bisimulation metrics, in which the Kantorovich lifting is parametrized with respect to a distance function. The standard bisimulation metrics, as well as metrics aimed at capturing multiplicative properties such as differential privacy, are specific instances of this general definition

    Verification of Agent-Based Artifact Systems

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    Artifact systems are a novel paradigm for specifying and implementing business processes described in terms of interacting modules called artifacts. Artifacts consist of data and lifecycles, accounting respectively for the relational structure of the artifacts' states and their possible evolutions over time. In this paper we put forward artifact-centric multi-agent systems, a novel formalisation of artifact systems in the context of multi-agent systems operating on them. Differently from the usual process-based models of services, the semantics we give explicitly accounts for the data structures on which artifact systems are defined. We study the model checking problem for artifact-centric multi-agent systems against specifications written in a quantified version of temporal-epistemic logic expressing the knowledge of the agents in the exchange. We begin by noting that the problem is undecidable in general. We then identify two noteworthy restrictions, one syntactical and one semantical, that enable us to find bisimilar finite abstractions and therefore reduce the model checking problem to the instance on finite models. Under these assumptions we show that the model checking problem for these systems is EXPSPACE-complete. We then introduce artifact-centric programs, compact and declarative representations of the programs governing both the artifact system and the agents. We show that, while these in principle generate infinite-state systems, under natural conditions their verification problem can be solved on finite abstractions that can be effectively computed from the programs. Finally we exemplify the theoretical results of the paper through a mainstream procurement scenario from the artifact systems literature
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