Analyzing NSPK with the Applied Pi Calculus

We present a framework for describing and analyzing cryptography protocols based on the Applied Pi calculus. The Needham-Schroeder Publick Key protocol (NSPK for short) and its fixed version by Lowe are modeled in this framework. Authentication is analyzed with the bisimulation method. We get that NSPK is insecure even with only one corrupted party while the fixed version is secure as long as there are two honest parties.