Abstract

Abstract. We investigate the composition of protocols that share a common secret. This situation arises when users employ the same password on different services. More precisely we study whether resistance against guessing attacks composes when a same password is used. We model guessing attacks using a common definition based on static equivalence in a cryptographic process calculus close to the applied pi calculus. We show that resistance against guessing attacks composes in the presence of a passive attacker. However, composition does not preserve resistance against guessing attacks for an active attacker. We therefore propose a simple syntactic criterion under which we show this composition to hold. Finally, we present a protocol transformation that ensures this syntactic criterion and preserves resistance against guessing attacks. 1

Citations