Abstract
The Signal protocol is used by billions of people for instant messaging in applications such as Facebook Messenger, Google Messages, Signal, Skype, and WhatsApp. However, advances in quantum computing threaten the security of the cornerstone of this protocol: the Diffie-Hellman key exchange. There actually are resistant alternatives, called post-quantum secure, but replacing the Diffie-Hellman key exchange with these new primitives requires a deep revision of the associated security proof. While the security of the current Signal protocol has been extensively studied with hand-written proofs and computer-verified symbolic analyses, its quantum-resistant variants lack symbolic security analyses.
In this work, we present the first symbolic security model for post-quantum variants of the Signal protocol. Our model focuses on the core state machines of the two main sub-protocols of Signal: the X3DH handshake, and the so-called double ratchet protocol. Then we show, with an automated proof using the Tamarin prover, that instantiated with the Hashimoto-Katsumata-Kwiatkowski-Prest post-quantum Signal’s handshake from PKC’21, and the Alwen-Coretti-Dodis KEM-based double ratchet from EUROCRYPT’19, the resulting post-quantum Signal protocol has equivalent security properties to its current classical counterpart.
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Acknowledgement
We wish to thanks Matthieu Giraud and Renaud Dubois for help on the Tamarin prover as well as helping discussions on the subject and the reviewers for highlighting some typos. First and last authors were supported by ANRT under the program CIFRE N\(^{\circ }\) 2021/0645 and N\(^{\circ }\) 2019/1583.
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Beguinet, H., Chevalier, C., Ricosset, T., Senet, H. (2024). Formal Verification of a Post-quantum Signal Protocol with Tamarin. In: Ben Hedia, B., Maleh, Y., Krichen, M. (eds) Verification and Evaluation of Computer and Communication Systems. VECoS 2023. Lecture Notes in Computer Science, vol 14368. Springer, Cham. https://doi.org/10.1007/978-3-031-49737-7_8
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