A computational group theoretic symmetry reduction package for the SPIN model checker

Symmetry reduced model checking is hindered by two problems: how to identify state space symmetry when systems are not fully symmetric, and how to determine equivalence of states during search. We present TopSpin, a fully automatic symmetry reduction package for the Spin model checker. TopSpin uses the Gap computational algebra system to effectively detect state space symmetry from the associated Promela specification, and to choose an efficient symmetry reduction strategy by classifying automorphism groups as a disjoint/wreath product of subgroups. We present encouraging experimental results for a variety of Promela examples

Probabilistic Anonymity

The concept of anonymity comes into play in a wide range of situations, varying from voting and anonymous donations to postings on bulletin boards and sending mails. A formal definition of this concept has been given in literature in terms of nondeterminism. In this paper, we investigate a notion of anonymity based on probability theory, and we we discuss the relation with the nondeterministic one. We then formulate this definition in terms of observables for processes in the probabilistic $pi$-calculus, and propose a method to verify automatically the anonymity property. We illustrate the method by using the example of the dining cryptographers

A Framework for Analyzing Probabilistic Protocols and Its Application to the Partial Secrets Exchange

We propose a probabilistic variant of the pi-calculus as a framework to specify randomized security protocols and their intended properties. In order to express an verify the correctness of the protocols, we develop a probabilistic version of the testing semantics. We then illustrate these concepts on an extended example: the Partial Secret Exchange, a protocol which uses a randomized primitive, the Oblivious Transfer, to achieve fairness of information exchange between two parties

Concurrency, σ-algebras, and probabilistic fairness ∗

We extend previous constructions of probabilities for a prime event structure E by allowing arbitrary confusion. Our study builds on results related to fairness in event structures that are of interest per se. Executions of E are captured by the set Ω of maximal configurations. We show that the information collected by observing only fair executions of E is confined in some σ-algebra F0, contained in the Borel σ-algebra F of Ω. Equality F0 = F holds when confusion is finite (formally, for the class of locally finite event structures), but inclusion F0 ⊆ F is strict in general. We show the existence of an increasing chain F0 ⊆ F1 ⊆ F2 ⊆... of subσ-algebras of F that capture the information collected when observing executions of increasing unfairness. We show that, if the event structure unfolds a 1-safe net, then unfairness remains quantitatively bounded, that is, the above chain reaches F in finitely many steps. The construction of probabilities typically relies on a Kolmogorov extension argument. Such arguments can achieve the construction of probabilities on the σ-algebra F0 only, while one is interested in probabilities defined on the entire Borel σ-algebra F. We prove that, when the event structure unfolds a 1-safe net, then unfair executions all belong to some set of F0 of zero probability. Whence F0 = F modulo 0 always holds, whereas F0 = F in general. This yields a new construction of Markovian probabilistic nets, carrying a natural interpretation that “unfair executions possess zero probability”