SAT-based model-checking of security protocols using planning graph analysis

In previous work we showed that automatic SAT-based model-checking techniques based on a reduction of protocol insecurity problems to satisfiability problems in propositional logic (SAT) can be used effectively to find attacks on security protocols. The approach results from the combination of a reduction of protocol insecurity problems to planning problems and well-known SAT-reduction techniques, called linear encodings, developed for planning. Experimental results confirmed the effectiveness of the approach but also showed that the time spent to generate the SAT formula largely dominates the time spent by the SAT solver to check its satisfiability. Moreover, the SAT instances generated by the tool get of unmanageable size on the most complex protocols. In this paper we explore the application of the Graphplan-based encoding technique to the analysis of security protocols and present experimental data showing that Graphplan-based encodings are considerably (i.e. up to 2 orders of magnitude) smaller than linear encodings. These results confirm the effectiveness of the SAT-based approach to the analysis of security protocols and pave the way to its application to large protocols arising in practical applications.