Stéphanie Delaune , Steve Kremer and Mark D . Ryan Symbolic bisimulation for the applied pi calculus Research Report LSV - 07 - 14 April 2007

We propose a symbolic semantics for the finite applied pi calculus, which is a variant of the pi calculus with extensions for modelling cryptgraphic protocols. By treating inputs symbolically, our semantics avoids potentially infinite branching of execution trees due to inputs from the environment. Correctness is maintained by associating with each process a set of constraints on symbolic terms. Based on the semantics, we define a sound symbolic labelled bisimulation relation. This is an important step towards automation of observational equivalence for the finite applied pi calculus, e.g., for verification of anonymity or strong secrecy properties of protocols with a bounded number of sessions.