SMT Solvers as Efficient Tools for Automatic Time Properties Verification of Security Protocols

Abstract

This paper presents our next research related to the use of SMT techniques for the analysis of security protocols. The behaviours of users and their changing knowledge during an investigated protocol executions are modelled as networks of communicating timed automata. The time properties are defined as the reachability properties of some, properly indicated states in the product automaton. We can do it using specially described time conditions, that can express dependencies between defined as a reachability property of some, chosen states in automata network, the possibility of performing some desired protocol steps and filling time constraints that use generation time of timestamps and lifetimes or/and networks delays. For our experiments we use boolean and SMT encodings that are the basis for respectively, SAT-and SMT-based bounded model checking. For SMT, the runs in product automaton are translated into the quantifier-free first-order formula. So far, we have implemented a well known bounded model checking algorithm and evaluated it for Needham-Schroeder Public Key, Needham Schroeder Symmetric Key, Woo Lam Pi and Wide Mouth Frog protocols. Now we show the tests carried out for the group of four known from the literature security protocols. We also compared our new SMT-based approach with a previous, only SAT-based, technique. For experiments, we used Minisat SAT solver, Z3, Yices2, CVC4 and MathSAT SMT solvers.