RHQC: post-quantum ratcheted key exchange from coding assumptions

Julien Juaneda; Marina Dehez-Clementi; Jean-Christophe Deneuville; Jérôme Lacan

Paper 2025/481

RHQC: post-quantum ratcheted key exchange from coding assumptions

Julien Juaneda , TéSA, Fédération ENAC ISAE-SUPAERO ONERA, University of Toulouse

Marina Dehez-Clementi

, Fédération ENAC ISAE-SUPAERO ONERA, University of Toulouse

Jean-Christophe Deneuville

, Fédération ENAC ISAE-SUPAERO ONERA, University of Toulouse

Jérôme Lacan

, Fédération ENAC ISAE-SUPAERO ONERA, University of Toulouse

Abstract

Key Exchange mechanisms (KE or KEMs) such as the Diffie-Hellman protocol have proved to be a cornerstone conciliating the efficiency of symmetric encryption and the practicality of public key primitives. Such designs however assume the non-compromission of the long term asymmetric key in use. To relax this strong security assumption, and allow for modern security features such as Perfect Forward Secrecy (PFS) or Post Compromise Security (PCS), Ratcheted-KE (RKE) have been proposed. This work proposes to turn the Hamming Quasi-Cyclic (HQC) cryptosystem into such a Ratcheted-KE, yielding the first code-based such construction. Interestingly, our design allows indifferently one party to update the key on-demand rather than the other, yielding a construction called bi-directional RKE, which compares favorably to generic transformations. Finally, we prove that the resulting scheme satisfies the usual correctness and key-indistinguishability properties, and suggest concrete sets of parameters, assuming different real-life use cases.

Note: Submitted to an International Conference, currently under review.

Metadata

Available format(s): PDF
Category: Public-key cryptography
Publication info: Preprint.
Keywords: Ratcheted Key Exchange Coding Perfect Forward Secrecy Post-Compromise Security Post-Quantum
Contact author(s): julien juaneda @ isae-supaero fr
marina dehez-clementi @ isae-supaero fr
jean-christophe deneuville @ enac fr
jerome lacan @ isae-supaero fr
History: 2025-03-14: approved; 2025-03-13: received; See all versions
Short URL: https://ia.cr/2025/481
License: CC BY

BibTeX

@misc{cryptoeprint:2025/481,
      author = {Julien Juaneda  and Marina Dehez-Clementi and Jean-Christophe Deneuville and Jérôme Lacan},
      title = {{RHQC}: post-quantum ratcheted key exchange from coding assumptions},
      howpublished = {Cryptology {ePrint} Archive, Paper 2025/481},
      year = {2025},
      url = {https://eprint.iacr.org/2025/481}
}