Safe simplifying transformations for security protocols or not just the Needham Schroeder pubic key protocol

Recent techniques for analyzing security protocols have tended to concentrate upon the small protocols that are typically found in the academic literature. However there is a huge gulf between these and most large commercial protocols: the latter typically have many more fields, and much higher levels of nested encryption. As a result, existing techniques are difficult to apply directly to these large protocols. In this paper we develop the notion of safe simplifying transformations: transformations that have the property of preserving insecurities; the effect of such transformations is that if we can verify the transformed protocol, then we will have verified the original protocol. We identify a number of such safe simplifying transformations, and use them in the analysis of a commercial protocol