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742 résultats

• • Séminaire

  • Cryptographie

  The probability that a F_q-hypersurface is smooth

  • 27 juin 2008

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

  Orateur : Jeroen Demeyer - Universiteit Gent

  Consider the projective space P^n over a finite field F_q. A hypersurface is defined by one homogenous equation with coefficients in F_q. For d going to infinity, we show that the probability that a hypersurface of degree d is nonsingular approaches 1/\zeta_{P^n (n+1)}. This is analogous to the well-known fact that the probability that an integer is squarefree equals 1/\zeta(2) = 6/\pi^2. This[…]

• • Séminaire

  • Cryptographie

  Explicit Serre-Tate theory and applications

  • 26 octobre 2007

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

  Orateur : 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[…]

• • Séminaire

  • Cryptographie

  Forward-Secure Signatures in Untrusted Update Environments:

  • 18 avril 2008

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

  Orateur : 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[…]

• • Séminaire

  • Cryptographie

  Délégation de déchiffrement en cryptographie asymétrique

  • 11 janvier 2008

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

  Orateur : Damien Vergnaud - ENS

  In 1998, Blaze, Bleumer, and Strauss proposed a cryptographic primitive called proxy re-encryption, in which a proxy transforms - without seeing the corresponding plaintext - a ciphertext computed under Alice's public key into one that can be opened using Bob's secret key. Recently, an appropriate definition of chosen-ciphertext security and a construction fitting this model were put forth by[…]

• • Séminaire

  • Cryptographie

  Nouveaux résultats en signature basée sur des codes correcteurs d'erreurs

  • 30 mai 2008

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

  Orateur : Pierre-Louis Cayrel - Limoges

  Je présenterai dans un premier temps la cryptographie basée sur les codes correcteurs d'erreurs (schéma de McEliece, Niederreiter) puis je détaillerai le schéma d'identification et de signature de Stern présenté à CRYPTO en 1993 et le schéma de signature de Courtois-Finiasz-Sendrier (ASIACRYPT 2001). Je présenterai ensuite 3 travaux récents sur ce sujet :<br/> - une construction sécurisée du[…]

• • Séminaire

  • Cryptographie

  Point counting in families of hyperelliptic curves

  • 23 juin 2006

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

  Orateur : 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[…]