Equivalence Properties by Typing in Cryptographic Branching Protocols

Véronique Cortier (1) , Niklas Grimm (2) , Joseph Lallemand (1) , Matteo Maffei (2)

1 PESTO - Proof techniques for security protocols
2 TU Wien - Vienna University of Technology = Technische Universität Wien

Recently, many tools have been proposed for automatically analysing, in symbolic models, equivalence of security protocols. Equivalence is a property needed to state privacy properties or game-based properties like strong secrecy. Tools for a bounded number of sessions can decide equivalence but typically suffer from efficiency issues. Tools for an unbounded number of sessions like Tamarin or ProVerif prove a stronger notion of equivalence (diff-equivalence) that does not properly handle protocols with else branches. Building upon a recent approach, we propose a type system for reasoning about branching protocols and dynamic keys. We prove our type system to entail equivalence , for all the standard primitives. Our type system has been implemented and shows a significant speedup compared to the tools for a bounded number of sessions, and compares similarly to ProVerif for an unbounded number of sessions. Moreover, we can also prove security of protocols that require a mix of bounded and unbounded number of sessions, which ProVerif cannot properly handle.

Domaines: Cryptographie et sécurité [cs.CR]

Véronique Cortier, Niklas Grimm, Joseph Lallemand, Matteo Maffei. Equivalence Properties by Typing in Cryptographic Branching Protocols. [Research Report] Université de Lorraine, CNRS, Inria, LORIA; TU Wien. 2018. ⟨hal-01715957⟩