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
-
Verification of Rust Cryptographic Implementations with Aeneas
Orateur : Aymeric Fromherz - Inria
From secure communications to online banking, cryptography is the cornerstone of most modern secure applications. Unfortunately, cryptographic design and implementation is notoriously error-prone, with a long history of design flaws, implementation bugs, and high-profile attacks. To address this issue, several projects proposed the use of formal verification techniques to statically ensure the[…] -
On the average hardness of SIVP for module lattices of fixed rank
Orateur : Radu Toma - Sorbonne Université
In joint work with Koen de Boer, Aurel Page, and Benjamin Wesolowski, we study the hardness of the approximate Shortest Independent Vectors Problem (SIVP) for random module lattices. We use here a natural notion of randomness as defined originally by Siegel through Haar measures. By proving a reduction, we show it is essentially as hard as the problem for arbitrary instances. While this was[…] -
Endomorphisms via Splittings
Orateur : Min-Yi Shen - No Affiliation
One of the fundamental hardness assumptions underlying isogeny-based cryptography is the problem of finding a non-trivial endomorphism of a given supersingular elliptic curve. In this talk, we show that the problem is related to the problem of finding a splitting of a principally polarised superspecial abelian surface. In particular, we provide formal security reductions and a proof-of-concept[…]-
Cryptography
-