Formal Models and Techniques for Analyzing Security Protocols: A Tutorial

International audienceSecurity protocols are distributed programs that aim at securing communications by the means of cryptography. They are for instance used to secure electronic payments, home banking and more recently electronic elections. Given The financial and societal impact in case of failure, and the long history of design flaws in such protocol, formal verification is a necessity. A major difference from other safety critical systems is that the properties of security protocols must hold in the presence of an arbitrary adversary. The aim of this paper is to provide a tutorial to some modern approaches for formally modeling protocols, their goals and automatically verifying them

Security protocols, constraint systems, and group theories

When formally analyzing security protocols it is often important to express properties in terms of an adversary’s inability to distinguish two protocols. It has been shown that this problem amounts to deciding the equivalence of two constraint systems, i.e., whether they have the same set of solutions. In this paper we study this equivalence problem when cryptographic primitives are modeled using a group equational theory, a special case of monoidal equational theories. The results strongly rely on the isomorphism between group theories and rings. This allows us to reduce the problem under study to the problem of solving systems of equations over rings. We provide several new decidability and complexity results, notably for equational theories which have applications in security protocols, such as exclusive or and Abelian groups which may additionally admit a unary, homomorphic symbol