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    • Seminar

    • Cryptography

    On the hardness of the NTRU problem

    • October 08, 2021

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Alice Pellet-Mary - CNRS, Institut Mathématiques de Bordeaux

    The NTRU problem is an algorithmic problem over structured lattices that was introduced by Hoffstein, Pipher, and Silverman more than 20 years ago, and which has been used to construct various cryptographic primitives. However, its relation to other lattice problems is still not well understood.<br/> In this talk, we will describe different variants of the NTRU problem, and study how they compare[…]
    • Seminar

    • Cryptography

    Implicit proofs of membership

    • March 13, 2020

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Olivier Blazy - Université Limoges

    Smooth hash proof systems have been introduced by Cramer and shoup to build compact efficient cca2 encryption in the standard model. Since then, they found applications in a broad range of protocols from oblivious transfer to authenticated key exchange, passing by witness examples.<br/> In this talk, we will start by a panorama of languages that can be managed by such a primitive and then show how[…]
    • Seminar

    • Cryptography

    A Concrete Treatment of Efficient Continuous Group Key Agreement via Multi-Recipient PKEs

    • November 19, 2021

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Thomas Prest - PQShield

    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[…]
    • Seminar

    • Cryptography

    Middle-Product Learning with Rounding Problem and its Applications

    • April 17, 2020

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Katharina Boudgoust - Univ Rennes, CNRS, IRISA

    This talk focuses on a new variant of the Learning With Errors (LWE) problem, a fundamental computational problem used in lattice-based cryptography.<br/> At Crypto17, Roşca et al. introduced the Middle-Product LWE problem (MP-LWE), whose hardness is based on the hardness of the Polynomial LWE (P-LWE) problem parameterized by a large set of polynomials, making it more secure against the possible[…]
    • Seminar

    • Cryptography

    Soutenance de thèse: Conception de courbes elliptiques et applications

    • December 16, 2021

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Rémi Clarisse - Rennes

    Le thème de la sécurité de l’information est prédominant dans nos vies actuelles. En particulier, les utilisateurs de service, plus précisément en ligne, s’attendent de plus en plus à ce que leurs données à caractère personnel soient traitées dignement et avec leur consentement. Cela incite donc à concevoir des systèmes se pliant à de telles exigences. Le recours à la cryptographie permet de[…]
    • Seminar

    • Cryptography

    Computing isogenies from modular equations in genus 2

    • January 10, 2020

    • IRMAR - Université de Rennes - Campus Beaulieu Bat. 22, RDC, Rennes - Amphi Lebesgue

    Speaker : Jean Kieffer - Université Bordeaux 1

    Given two l-isogenous elliptic curves, a well-known algorithm of Elkies uses modular polynomials to compute this isogeny explicitly. In this work, we generalize his ideas to Jacobians of genus 2 curves. Our algorithms works for both l-isogenies and (in the RM case) cyclic isogenies, and uses Siegel or Hilbert type modular equations respectively. This has applications for point counting in genus 2:[…]