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655 results

    • Seminar

    • Cryptography

    Explicit Serre-Tate theory and applications

    • October 26, 2007

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

    Speaker : Robert Carls - University of Ulm

    This talk is about joint work with David Lubicz. By a classical result of Serre and Tate the deformation space of an ordinary abelian variety is given by a formal torus. In Serre-Tate coordinates the problem of canonical lifting is trivial. Unfortunately, in general it is difficult to compute the Serre-Tate parameters of a given abelian variety. Alternatively, one may use canonical coordinates[…]
    • Seminar

    • Cryptography

    Forward-Secure Signatures in Untrusted Update Environments:

    • April 18, 2008

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

    Speaker : Benoit Libert - UCL

    Forward-secure signatures (FSS) prevent forgeries for past time periods when an attacker obtains full access to the signer's storage. To simplify the integration of these primitives into standard security architectures, Boyen, Shacham, Shen and Waters recently introduced the concept of forward-secure signatures with untrusted updates where private keys are additionally protected by a second factor[…]
    • Seminar

    • Cryptography

    Identification de diffusion illicite : le fingerprinting et les codes centrés

    • December 22, 2006

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

    Speaker : Fabien Galand - IRISA

    Dans le contexte de la distribution de contenu numérique, il est souvent souhaitable de pouvoir tracer l'origine des copies. Par exemple, lors de la vente de vidéos, l'acheteur n'est pas autorisé à redistribuer ce qu'il vient d'acheter. Lorsqu'il le fait, on souhaite pouvoir, à partir d'une des copies diffusées, l'identifier comme étant à l'origine de cette distribution illicite. Pour résoudre ce[…]
    • Seminar

    • Cryptography

    An l-adic CM construction for genus 2

    • June 01, 2007

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

    Speaker : David Kohel - University of Sydney

    We recall recent work on CM constructions using canonical lifts of the Frobenius isogeny: for p = 2 with Gaudry, Houtmann, Ritzenthaler, and Weng, and generalisation to p = 3 with Carls and Lubicz. I will explain how to extend this to (l,l)-isogenies for l = 2, 3 coprime to the characteristic.
    • Seminar

    • Cryptography

    Point counting in families of hyperelliptic curves

    • June 23, 2006

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

    Speaker : Hendrik Hubrechts - Leuven University

    Let p be a small prime number, F a field of characteristic p and extension degree n, and E a hyperelliptic curve over F. In cryptography one tries to exploit the hardness of determining a discrete logarithm on the jacobian of such curves. In order to achieve this it is important to know what the size of this jacobian is. This parameter can be deduced from the zeta function of the curve.<br/> We[…]
    • Seminar

    • Cryptography

    Efficient Intrusion-Resilient Signatures Without Random Oracle

    • February 02, 2006

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

    Speaker : Benoit Libert - Université Catholique de Louvain

    Intrusion-resilient signatures are key-evolving protocols that extend the concepts of forward-secure and key-insulated signatures. As in the latter schemes, time is divided into distinct periods where private keys are periodically updated while public keys remain fixed. Private keys are stored in both a user and a base; signature operations are performed by the user while the base is involved in[…]