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• • Séminaire

  • Cryptographie

  Gröbner Bases Techniques in Post-Quantum Cryptography

  • 12 juin 2015

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

  Orateur : Ludovic Perret - LIP6

  After the publication of Shor's algorithm, it became evident the most popular public-key cryptographic systems that rely on the integer factorization problem or on the discrete logarithm problem would be easily solvable using large enough quantum computers (if such quantum computers are ever built). That triggered a vivid interest in the research of cryptographic algorithms (mostly public-key[…]

• • Séminaire

  • Cryptographie

  Sanitization of FHE Ciphertexts

  • 12 février 2016

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

  Orateur : Damien Stehlé - ENS Lyon

  By definition, fully homomorphic encryption (FHE) schemes support homomorphic decryption, and all known FHE constructions are bootstrapped from a Somewhat Homomorphic Encryption (SHE) scheme via this technique. Additionally, when a public key is provided, ciphertexts are also re-randomizable, e.g. by adding to them fresh encryptions of~$0$. From those two operations we devise an algorithm to[…]

• • Séminaire

  • Cryptographie

  Multilinear Maps from Obfuscation

  • 21 octobre 2016

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

  Orateur : Pooya Farshim - ENS Paris

  We provide constructions of multilinear groups equipped with natural hard problems from indistinguishability obfuscation, homomorphic encryption, and NIZKs. This complements known results on the constructions of indistinguishability obfuscators from multilinear maps in the reverse direction.<br/> We provide two distinct, but closely related constructions and show that multilinear analogues of the[…]

• • Séminaire

  • Cryptographie

  Bornes de Weil généralisées pour le nombre de points d'une courbe projective lisse définie sur un corps fini.

  • 16 janvier 2015

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

  Orateur : Emmanuel Hallouin - Université de Toulouse 2

  Je commencerai par rappeler l'esprit de la preuve initiale de Weil pour la majoration du nombre de points d'une courbe projective lisse définie sur un corps fini. En particulier, j'insisterai sur le fait qu'elle découle de contraintes euclidiennes dans un espace euclidien bien choisi. Ensuite je montrerai comment cette borne de Weil peut être vue comme la borne d'ordre 1 d'une classe de bornes de[…]

• • Séminaire

  • Cryptographie

  How to find low-weight polynomial multiples.

  • 13 juin 2014

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

  Orateur : Carl Löndahl - Université de Lund

  We present an improved algorithm for finding low-weight multiples of polynomials over the binary field using coding heoretic methods. The associated code defined by the given olynomial has a cyclic structure, allowing an algorithm to earch for shifts of the sought minimum-weight odeword. Therefore, a code with higher dimension is onstructed, having a larger number of low-weight codewords nd[…]

• • Séminaire

  • Cryptographie

  Cryptanalysis of Round-Reduced PRINCE and TWINE

  • 27 mars 2015

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

  Orateur : Patrick Derbez - Luxembourg

  NXP Semiconductors and its academic partners challenged the cryptographic community with finding practical attacks on the block cipher they designed, PRINCE. In the first part of this talk we present new attacks on round-reduced PRINCE including the ones which won the challenge in the 6 and 8-round categories --- the highest for which winners were identified. Our first attacks rely on a meet-in[…]