Analysing Protocol Subject to Guessing Attacks

In this paper we consider guessing attacks upon security protocols, where an intruder guesses one of the values used (typically a poorly-chosen password) and then seeks to verify that guess. We formalise such attacks, and in particular the way in which the guess is verified. We then describe how to model such attacks within the process algebra CSP, so that they can be detected using the model checker FDR, and illustrate our technique on some examples.