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655 results
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Seminar
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Cryptography
Courbes elliptiques et attaques par canaux cachés
Speaker : Marc Joye - Gem+
Provable security becomes more and more popular in the cryptographic community. As exemplified by the NESSIE project, it is now common to see it as an attribute of a cryptosystem. Provable security is at the protocol level; a harder task may be to evaluate the security of a cryptosystem at the implementation level. Rather than considering a cryptosystem as a black-box, we may assume that some[…] -
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Seminar
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Cryptography
Packings on the Grassmann manifold: an interesting approach for non coherent space-time coding
Speaker : Jean-Claude Belfiore - ENST
The need of high data rates on the radio channel (WiFi and its future for example) explains the increasing number of researchers working on space-time codes. Preparing Wireless IP systems, some companies and some researchers are promoting the use of non coherent space-time codes.<br/> We show that designing a non coherent space-time code is equivalent to finding some good packings on the Grassmann[…] -
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Seminar
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Cryptography
Sur le calcul du corps de définition d'un point de torsion d'une jacobienne d'une courbe de genre quelconque
Speaker : Bas Edixhoven - Leiden University
En commençant par un calcul explicite sur une courbe elliptique, j'expliquerai ma stratégie pour calculer le corps de définition d'un point de torsion d'une jacobienne d'une courbe de genre quelconque. En gros, cette stratégie consiste à calculer le polynôme minimal d'une coordonnée d'un tel point par une approximation (complexe ou p-adique) avec une précision suffisante. J'expliquerai comment la[…] -
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Seminar
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Cryptography
Efficient arithmetic on (hyper-)elliptic curves over finite fields
Speaker : Tanja Lange - Ruhr-Universität Bochum
The talk will be concerned with arithmetic on elliptic and hyperelliptic curves. We show how fast the arithmetic can get by clever choices of the coordinates and present special kinds of curves which allow even faster arithmetic using the Frobenius endomorphism. For elliptic curves this has been used to achieve fast arithmetic for the past years. However, so far arithmetic in the ideal class group[…] -
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Seminar
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Cryptography
Calculs explicites autour du revêtement modulaire d'une courbe elliptique définie sur Q
Speaker : Christophe Delaunay
Dans cet exposé, nous montrerons comment donner une étude concrète du revêtement modulaire d'une courbe elliptique définie sur Q, f: X_0(N) \rightarrow E. Pour cela, nous utiliserons le point de vue analytique de f qui est plus adapté pour nos calculs. En particulier, nous expliquerons comment calculer le degré de cette application et nous donnerons une étude plus ou moins expérimentale des points[…] -
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Seminar
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Cryptography
Constructive Galois Theory
Speaker : Juergen Klueners - Universität Kassel
In constructive Galois theory, there are two main questions: the direct problem and the inverse problem. For the inverse problem the question is whether it is possible to find a polynomial such that the Galois group of that polynomial is a given finite group. In this talk, we will focus on the direct problem. Given a polynomial f we explain how to compute the Galois group of this polynomial. The[…] -