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655 results
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Seminar
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Cryptography
Bases normales elliptiques pour les corps finis (avec Reynald Lercier)
Speaker : Jean-Marc Couveignes - Université Toulouse I
Les bases normales permettent de calculer rapidement l'action de Frobenius pour les extensions de corps finis : l'action de Galois se réduit à une permutation cyclique des coordonnées. En revanche, dans de telles bases, la multiplication est souvent difficile.<br/> Les périodes de Gauss permettent de construire des bases normales où la multiplication est assez facile. Mais elle n'existent pas pour[…] -
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Seminar
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Cryptography
The probability that a F_q-hypersurface is smooth
Speaker : 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[…] -
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Seminar
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Cryptography
Explicit Serre-Tate theory and applications
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[…] -
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Seminar
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Cryptography
Forward-Secure Signatures in Untrusted Update Environments:
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[…] -
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Seminar
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Cryptography
Délégation de déchiffrement en cryptographie asymétrique
Speaker : 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[…] -
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Seminar
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Cryptography
Nouveaux résultats en signature basée sur des codes correcteurs d'erreurs
Speaker : 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[…] -