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Vérification de propriétés d'indistinguabilité pour les protocoles cryptographiques

Abstract : This thesis presents methods to verify cryptographic protocolsin the symbolic model: formal methods allowto verify that small distributed programssatisfy equivalence properties.Those properties state that an attackercannot decide what scenario is beeing played.Strong secrecy, and privacy type properties, like anonymityand unlinkeability, can be modelled through this formalism.Moreover, protocols are executed simultaneouslyby an unbounded number of agents, for an unbounded numberof sessions,which leads to indecidability results.So, we have either to consider an arbitrary number of sessions,and search for semi-decision proceduresand decidable classes;or to establish decision procedures for a finite numberof sessions.When we started the work presented in this thesis,the existing equivalence checkers in the bounded modelwere highly limited. They could only handlea~very small number of sessions (sometimes no more than three).This thesis presents efficient decision proceduresfor bounded verification of equivalence properties.Our first step is to provide small attack results.First, for deterministic processes, there existsan attack if, and ony if, there is a well-typed attack,assuming that there is no confusion between variable types.Second, when there exists a flaw,the attacker needs at most three constants to find it.Then, our second step is to translatethe indistinguishability problem as a reachability problemin a planning system. We solve this second problemthrough planning graph algorithm and SAT encoding.In a final step, we present the implementation ofthe SAT-Equiv tool, which allows us to evaluate our approach.In particular, a benchmark with comparable tools provesthe efficiency of SAT-Equiv.
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Submitted on : Monday, December 10, 2018 - 10:53:05 AM
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Antoine Dallon. Vérification de propriétés d'indistinguabilité pour les protocoles cryptographiques. Autre [cs.OH]. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLN044⟩. ⟨tel-01949500⟩

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