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PI-1930

F. Cassez, J. Dubreil, H. Marchand. Dynamic Observers for the Synthesis of Opaque Systems. Research Report IRISA, No 1930, May 2009.

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Abstract

In this paper, we address the problem of synthesizing opaque systems. A secret predicate S over the runs of a system G is opaque to an external user having partial observability over G, if s/he can never infer from the observation of a run of G that the run belongs to S. We first investigate the case of static partial observability where the set of events the user can observe is fixed a priori. In this context, we show that checking whether a system is opaque is PSPACE-complete, which implies that computing an optimal static observer ensuring opacity is also a PSPACE-complete problem. Next, we introduce dynamic partial observability where the set of events the user can observe changes over time. We show how to check that a system is opaque w.r.t. to a dynamic observer and also address the corresponding synthesis problem: given a system G and secret states S, compute the set of dynamic observers under which S is opaque. Our main result is that the set of such observers can be finitely represented and can be computed in EXPTIME

Contact

Hervé Marchand http://people.rennes.inria.fr/Herve.Marchand/

BibTex Reference

@TechReport{PI-1930,
   Author = {Cassez, F. and Dubreil, J. and Marchand, H.},
   Title = {Dynamic Observers for the Synthesis of Opaque Systems},
   Number = {1930},
   Institution = {IRISA},
   Month = {May},
   Year = {2009}
}

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