Application to key cycles

Abstract. The Maude-NRL Protocol Analyzer (Maude-NPA) is a tool and inference system for reasoning about the security of cryptographic protocols in which the cryptosystems satisfy different equational properties. It both extends and provides a formal framework for the original NRL Protocol Analyzer, which limited itself to an equational theory ∆ of convergent rewrite rules. In this paper we extend our framework to include theories of the form ∆ ⊎ B, where B is the theory of associativity and commutativity and ∆ is convergent modulo B. Order-sorted B-unification plays a crucial role; to obtain this functionality we describe a sort propagation algorithm that filters out unsorted B-unifiers provided by the CiME unification tool. We show how extensions of some of the state reduction techniques of the original NRL Protocol Analyzer can be applied in this context. We illustrate the ideas and capabilities of the Maude-NPA with an example involving the Diffie-Hellman key agreement protocol. 1

Web services send and receive messages in XML syntax with some parts hashed, encrypted or signed, according to the WS-Security standard. In this paper we introduce a model to formally describe the protocols that underly these services, their security properties and the rewriting attacks they might be subject to. Unlike other protocol models (in symbolic analysis) ours can handle non-deterministic receive/send actions and unordered sequence of XML nodes. Then to detect the attacks we have to consider the services as combining multiset operators and cryptographic ones and we have to solve specific satisfiability problems in the combined theory. By non-trivial extension of the combination techniques of [3] we obtain a decision procedure for insecurity of Web services with messages built using encryption, signature, and other cryptographic primitives. This combination technique allows one to decide insecurity in a modular way by reducing the associated constraint solving problems to problems in simpler theories.

c t i v it y e p o r t

e p o r t 2009 Table of contents

c t i v it y e p o r t 2007 Table of contents

Thèmes COM et NUM et SYM apport de recherche