Roles in cryptographic protocols

In protocols for the distribution of symmetric keys, a principal will usually either take on the role as a session key provider or as a session key user. A principal taking on the role as session key user may also act as the master or the slave. Methods for the analysis of cryptographic protocols that fail to properly handle multiple roles are demonstrated to yield undependable results. A protocol, KP, similar to the Needham and Schroeder symmetric key distribution protocol (1978) is presented. An example is provided to show how a multirole flaw in KP can be utilized by an adversary to obtain a session key. Using a method due to M. Burrows et al. (1989) and P. Bieber (1990) it is shown that KP seems to be suitable for secure key distribution. The approach due to P. Bieber is then modified to facilitate the detection of the class of multirole flaws