599 résultats
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An Automatic Security Protocol Verifier based on Resolution
Orateur : Bruno Blanchet - ENS
We present a technique for the verification of cryptographic protocols, based on an abstract representation of the protocol by a set of Horn clauses, and on a resolution algorithm on these clauses. This technique allows a flexible encoding of many cryptographic primitives. It can verify a wide range of security properties of the protocols, such as secrecy, authenticity, and limited cases of[…] -
Theta identities and Thomae formulas
Orateur : Yaacov Kopeliovich
In this talk we apply Thomae formulas to obtain algebraic relations satisfied by Riemann surfaces that are cyclic covers of the Sphere. We focus on the genus 2 case and then give an example of a higher genus case (g=4) that was not known before. The conjectural connection of these identities as well as Thomae formulas to the moduli action of the Braid group is explained.<br/> We present a[…] -
Bilinear Structures induced by the Lichtenbaum pairing and the
Orateur : Gerhard Frey - Essen University
Groups of prime order with a bilinear structure are interesting objects for public key cryptography. In the first part of the lecture we shall explain how the pairing on points of the Jacobian variety which is usually called "Tate-pairing" can be got in a p- adic setting by the Lichtenbaum pairing. On the one hand side this setting gives us more freedom for its computation which leads to[…] -
Blackbox Secret Sharing from Primitive Sets in Algebraic Number Fields
Orateur : Rolnald Cramer - CWI, Amsterdam & Mathematical Insitute, Leiden University
A {\em black-box} secret sharing scheme (BBSSS) for a given access structure works in exactly the same way over any finite Abelian group, as it only requires black-box access to group operations and to random group elements. In particular, there is no dependence on e.g.\ the structure of the group or its order. The expansion factor of a BBSSS is the length of a vector of shares (the number of[…] -
Relative rigid cohomology and the deformation method for elliptic curves
Orateur : Ralf Gerkmann - Universitat Mainz
By a well-known result of Dwork the zeta functions of the fibers in a one-parameter family of hypersurfaces can be described in terms of p-adic holomorphic functions. This result was used by A. Lauder in order to formulate a deter- ministic algorithm that computes the zeta function of a hypersurface in polynomial time. In this talk we describe a similiar method for elliptic curves which is based[…] -
Preuves de sécurité pour les systèmes de chiffrement à clé publique
Orateur : Robert Rolland - Université de Marseille
Cet exposé est un survol de l'état actuel de la théorie de la sécurité prouvée, en ce qui concerne le chiffrement à clé publique. Les principaux modèles d'adversaires ainsi que les principales fonctions de sécurité qu'on veut assurer sont présentés ainsi que les relations entre ces diverses notions. A partir du problème de Diffie-Hellman décisionnel, qu'on redéfinit sous[…]