Cortier, V., Grimm, N., Lallemand, J., & Maffei, M. (2018). Equivalence Properties by Typing in Cryptographic Branching Protocols. In L. Bauer & R. Küsters (Eds.), Principles of Security and Trust (pp. 160–187). Springer LNCS. https://doi.org/10.1007/978-3-319-89722-6_7
Recently, many tools have been proposed for automatically analysing, in symbolic models, equivalence of security protocols. Equiv- alence 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 rea- soning 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.
