Description
Continuous group key agreements (CGKAs) are a class of protocols that can provide strong security guarantees to secure group messaging protocols such as Signal and MLS. Protection against device compromise is provided by commit messages: at a regular rate, each group member may refresh their key material by uploading a commit message, which is then downloaded and processed by all the other members. In practice, propagating commit messages dominates the bandwidth consumption of existing CGKAs. We propose Chained CmPKE, a CGKA with an asymmetric bandwidth cost: in a group of N members, a commit message costs O(N) to upload and O(1) to download, for a total bandwidth cost of O(N). In contrast, TreeKEM costs Ω(log N) in both directions, for a total cost Ω(N logN). Our protocol relies on generic primitives, and is therefore readily post-quantum.<br/> We go one step further and propose post-quantum primitives that are tailored to Chained CmPKE, which allows us to cut the growth rate of uploaded commit messages by two or three orders of magnitude compared to naive instantiations. Finally, we realize a software implementation of Chained CmPKE. Our experiments show that even for groups with a size as large as N=2^10, commit messages can be computed and processed in less than 100 ms.<br/> This talk is based on joint work with Keitaro Hashimoto, Shuichi Katsumata, Eamonn Postlethwaite and Bas Westerbaan. Link to the full article: https://eprint.iacr.org/2021/1407.<br/> lien: https://univ-rennes1-fr.zoom.us/j/97066341266?pwd=RUthOFV5cm1uT0ZCQVh6QUcrb1drQT09
Prochains exposés
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Module Learning With Errors and Structured Extrapolated Dihedral Cosets
Orateur : Jinwei Zheng - Télécom Paris
The Module Learning With Errors (MLWE) problem is the fundamental hardness assumption underlying the key encapsulation and signature schemes ML-KEM and ML-DSA, which have been selected by NIST for post-quantum cryptography standardization. Understanding its quantum hardness is crucial for assessing the security of these standardized schemes. Inspired by the equivalence between LWE and[…]-
Cryptography
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European Cyber Week: atelier cryptographie post-quantique
Dans la continuité des éditions 2021, 2022 et 2024, la DGA — en partenariat avec CREACH LABS et avec le soutien de l'ANSSI, de l'IRISA, de l'IRMAR et du Pôle d'Excellence Cyber — organise la 4e édition de l'atelier consacré à la cryptographie post-quantique dans le cadre de l'European Cyber Week 2026. Attention, il faut s'inscrire (gratuitement) au préalable — s'inscrire à la conférence Les[…] -
Post-quantum day of the cryptography seminar
A scientific day devoted to post-quantum cryptography, held in the wake of the European Cyber Week, with talks more technical than those presented at the ECW.