Information Security Seminar 

06/10/2009, 16:15 — 17:15 — Room P4.35, Mathematics Building
Bruno Montalto, ETH Zurich, Switzerland

Deciding Security Against Offline Guessing Attacks under Equational Theories

Offline guessing (or dictionary) attacks are one of the most common vulnerabilities of security protocols. Previous formalizations of offline guessing attacks are essentially extensions of the standard Dolev-Yao model for security protocol analysis with inference rules which model the attacker's guessing capability, such as those proposed by Lowe. However, as pointed out by Vigano et. al., such a set of rules is specialized to a particular set of cryptographic primitives and intruder capabilities, and it is difficult to convince oneself of its completeness. In line with this work, we propose a symbolic method based on equational theories and provide a simple yet general definition of offline guessing attack in our model. We also show that, for a particular but relevant class of equational theories, the problem of deciding whether an attacker can mount an offline guessing attack from a set of terms learned during protocol execution is decidable in polynomial-time, mimicking a result by Delaune and Jacquemard for Lowe's model.