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2 événements

  • Cryptographie

    Jeudi 20 avril 11:00-12:00 - Gaëtan Leurent (Inria Paris)

    Breaking Symmetric Cryptosystems Using Quantum Algorithms

    Résumé : Due to Shor’s algorithm, quantum computers are a severe threat for public key cryptography. This motivated the cryptographic community to search for quantum-safe solutions. On the other hand, the impact of quantum computing on secret key cryptography is much less understood. The main known applicable result is Grover’s algorithm that gives a quadratic speed-up for exhaustive search. In this talk, we examine more closely the security of symmetric ciphers against quantum attacks, both against primitives, and against modes of operation.
    First we show that a quantum procedure called Simon’s algorithm can dramatically speed up several attacks. We consider a model where an adversary can query an oracle implementing a cryptographic primitive in a quantum superposition of different states. This model gives a lot of power to the adversary, but recent results show that it is nonetheless possible to build secure cryptosystems in it. We show that the most widely used modes of operation for authentication and authenticated encryption (e.g. CBC-MAC, PMAC, GMAC, GCM, and OCB) are completely broken in this security model.
    Next, we investigate quantum cryptanalysis techniques, because our trust in symmetric ciphers relies mostly on their ability to resist cryptanalysis techniques. More specifically, we consider quantum versions of differential and linear cryptanalysis. We show that it is usually possible to use quantum computations to obtain a quadratic speed-up for these attack techniques, but the situation must be nuanced : we don’t get a quadratic speed-up for all variants of the attacks.

    Lieu : Bât. Descartes, Salle Ératosthène

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  • jeunes

    Jeudi 20 avril 15:15-16:15 - Élise Barelli - INRIA

    Codes alternants géométriques pour le schéma de McEliece

    Résumé : Le schéma de chiffrement de McEliece est un système de chiffrement à clé publique basé sur l’utilisation de code correcteurs d’erreurs. En 1996, Janwa et Moreno ont proposé l’utilisation des codes géométriques pour ce schéma et en particulier les sous-codes sur un sous corps de codes géométriques, que nous notons codes alternants géométriques. On se demande si ces codes géométriques sont de bons candidats pour le schéma de McEliece et s’il est possible de construire des clés compactes à partir de ces codes.

    Lieu : Amphi H

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