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X-WR-CALNAME:GREYC UMR CNRS 6072 - Groupe de Recherche en Informatique, Image, et Instrumentation de Caen
X-ORIGINAL-URL:https://www.greyc.fr
X-WR-CALDESC:évènements pour GREYC UMR CNRS 6072 - Groupe de Recherche en Informatique, Image, et Instrumentation de Caen
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TZID:Europe/Paris
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DTSTART:20250330T010000
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DTSTART:20251026T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250416T140000
DTEND;TZID=Europe/Paris:20250416T150000
DTSTAMP:20260421T102655
CREATED:20250404T100723Z
LAST-MODIFIED:20250404T100753Z
UID:11821-1744812000-1744815600@www.greyc.fr
SUMMARY:Kévin Carrier - Combinatorial Attacks On The Decoding Problem
DESCRIPTION:The decoding problem is fundamental in post-quantum cryptography. It can be broadly described as essentially solving a linear system with a non-linear constraint on the solution. Phrased this way\, the problem applies to both code-based and lattice-based cryptography. For example\, the linear system may be defined over FF_q\, with the non-linear constraint being a condition on the Hamming weight of the solution (McEliece\, BIKE\, HQC\, Wave\, SDitH…) or even a condition on the subgroup in which the solution resides (CROSS). The system may also be defined over FF_q^m\, with the non-linear constraint being a condition on the rank of the vector space spanned by the solution vectors (Mirath\, Ryde). In lattice-based cryptography\, the system is generally defined over ZZ_q\, with the non-linear constraint being a condition on the Euclidean length of the solution (Kyber\, Falcon\, Dilithium\, Hawk…). The list above is far from exhaustive and can extend to other areas such as Fully Homomorphic Encryption (FHE) or the blind code recognition problem (reverse of telecomunication). \nCombinatorial techniques for solving the decoding problem (in both codes and lattices) can be classified into two categories: primal attacks and dual attacks. Primal attacks aim to recover a set of information about the solution\, essentially a compressed description of the solution. Exhaustive search can then be accelerated using techniques like the Birthday Paradox (collision search). More recently\, techniques based on nearest-neighbor searches have emerged and significantly sped up primal attacks. The nearest-neighbor problem involves finding close pairs in a list. The notion of closeness can be extended to adapt to the non-linear constraint of the original decoding problem. However\, this requires adapting known techniques to these different variants of the nearest-neighbor problem. \nIt turns out that primal decoding techniques are often more effective when there are few equations in the system relative to the number of unknowns. Therefore\, when the number of equations is close to the number of unknowns\, is it possible to reduce the problem to another decoding problem where the number of equations is smaller? One approach to this is to dualize the decoding problem: instead of searching for a solution in a specific subspace\, could we reduce the problem to finding a solution in the orthogonal/dual subspace? Some recent attacks\, known as dual attacks\, offer an initial attempt at such a reduction. However\, dual attacks are a topic of controversy. In particular\, the recent dual attack by Matzov\, which claims to significantly lower the security level of Kyber\, a lattice-based cryptosystem currently being standardized by NIST\, has not been widely accepted. The analysis behind this attack relies on a set of assumptions that\, in certain scenarios\, have been shown to contradict established theorems or well-tested heuristics. Nonetheless\, we present new techniques for analyzing dual attacks. Specifically\, we avoid the same independence assumption made in Matzov’s work\, allowing us to reassess the complexity of dual attacks on Kyber and demonstrate that its security levels fall below the NIST requirements.
URL:https://www.greyc.fr/event/kevin-carrier-combinatorial-attacks-on-the-decoding-problem/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250422T104500
DTEND;TZID=Europe/Paris:20250422T114500
DTSTAMP:20260421T102655
CREATED:20250416T143631Z
LAST-MODIFIED:20250416T143631Z
UID:11824-1745318700-1745322300@www.greyc.fr
SUMMARY:Séminaire Algorithmique : Josselin Guéneron (GREYC) « Repeated Stochastic Coalition Formation: representations and algorithmic approaches »
DESCRIPTION:Coalition formation is a cooperative game theory framework in which a set of agents\, required to perform implicit or explicit tasks\, must be divided into subgroups (called coalitions)\, according to collective criteria and a utility function describing the utility of each coalition. This is equivalent to a problem of partitioning the set of agents. The classic problem is to find a coalition structure (i.e. partitioning) that maximizes social welfare (sum of the utilities generated by the coalitions). A number of algorithmic approaches exist\, based on the exploration of a representation of the solution space\, in the form of an exhaustive lattice or integer partitions. However\, the classical approach to coalition formation assumes that agents have perfect knowledge of the utilities of coalitions\, and that these are deterministic\, which is not representative of the actual application problems we may encounter. \nWe are therefore interested in exploring algorithmic solutions for a stochastic and repeated context of coalition formation\, where agents have no a priori knowledge of utilities\, which are now stochastic. In this context\, classical representations (lattices\, integer partitions) and algorithms show limitations. We are exploring approaches based on Monte-Carlo tree search methods\, as well as the search for a suitable representation.
URL:https://www.greyc.fr/event/seminaire-algorithmique-josselin-gueneron-greyc-repeated-stochastic-coalition-formation-representations-and-algorithmic-approaches/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250429T104500
DTEND;TZID=Europe/Paris:20250429T114500
DTSTAMP:20260421T102655
CREATED:20250416T143759Z
LAST-MODIFIED:20250416T143759Z
UID:11826-1745923500-1745927100@www.greyc.fr
SUMMARY:Séminaire Algorithmique : Nicolas Bitar (LAMFA\, Univ. Picardie)\, « Subshifts of finite type and quasi-isometries beyond groups »
DESCRIPTION:In 1964\, R. Berger proved the existence of strongly aperiodic subshifts of finite type (SFT) on $\mathbb{Z}^2$\, and used them to prove the undecidability of the Domino Problem. With the goal of understanding what aspects of $\mathbb{Z}^2$ account for this result\, there has been an effort in recent years to characterize the groups with undecidable Domino Problem\, and groups that admit strongly aperiodic SFTs. A key result in this direction is a result by Cohen that states that both the decidability of the Domino Problem and the existence of strongly aperiodic SFTs are quasi-isometry invariants for finitely presented groups. In this talk\, I will explain how to generalize this result to new structures called blueprints. I will show how this generalizes results from the literature that use structures other than groups\, and use the result to show that the Domino Problem for multidimensional geometric tilings is undecidable.\n\nThis is joint work with Sebastián Barbieri.
URL:https://www.greyc.fr/event/seminaire-algorithmique-nicolas-bitar-lamfa-univ-picardie-subshifts-of-finite-type-and-quasi-isometries-beyond-groups/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250429T140000
DTEND;TZID=Europe/Paris:20250429T150000
DTSTAMP:20260421T102655
CREATED:20250429T091630Z
LAST-MODIFIED:20250429T091630Z
UID:11840-1745935200-1745938800@www.greyc.fr
SUMMARY:Tristan Benoît - Approche multimodale pour la génération de noms de fonctions à partir du code binaire
DESCRIPTION:La compréhension du code binaire est cruciale en rétro-ingénierie. Usuellement\, des bases de fonctions servent à identifier dans un binaire les fonctions proches de références connues. Cependant\, souvent les projections sous-jacentes traitent chaque code source séparément. En revanche\, les modèles de langage récents permettent de projeter le code binaire et sa description textuelle dans un même espace vectoriel\, et d’associer des codes binaires ayant des fonctionnalités proches. \nPlus simplement\, il est aussi possible de générer une description sémantique ou un nom de fonction directement\, sans rechercher une fonction proche. Plusieurs méthodes reposent sur des architectures de type transformer\, et visent à traduire du langage binaire vers le langage naturel. Notre nouvelle méthode\, BLens\, inspirée des architectures multimodales pour le sous-titrage d’images\, utilise différentes projections de l’état de l’art et les découpe en morceaux pour améliorer la génération des noms. Après un pré-entraînement basé sur une double tâche multimodale (« contrastive captioning »)\, un nouveau décodeur est ensuite ajouté pour la génération des noms. \nNous montrerons que cette approche surpasse les méthodes existantes\, y compris lors de la nomination de fonctions inédites. Nous discuterons aussi des défis liés à l’évaluation des résultats et à la généralisation\, face à la spécificité ou la réutilisation des codes sources. Enfin\, nous présenterons des pistes futures\, comme l’intégration de modules capables de détecter automatiquement des types ou de suggérer des noms de variables\, pour des annotations complètes et adaptées à l’usage des spécialistes.
URL:https://www.greyc.fr/event/tristan-benoit-approche-multimodale-pour-la-generation-de-noms-de-fonctions-a-partir-du-code-binaire/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250430T140000
DTEND;TZID=Europe/Paris:20250430T150000
DTSTAMP:20260421T102655
CREATED:20250424T135623Z
LAST-MODIFIED:20250424T135623Z
UID:11838-1746021600-1746025200@www.greyc.fr
SUMMARY:Mengce Zheng - Lattice-based solving strategy using Coppersmith's techniques and its applications
DESCRIPTION:Lattice-based cryptanalysis using Coppersmith’s techniques has emerged as a powerful approach to compromising the security of several cryptographic algorithms under specific conditions. This talk will provide an exploration of the lattice-based solving strategy\, which leverages lattice basis reduction to find small roots of polynomial equations modulo an integer. This method is then used for examining its practical applications in RSA cryptanalysis\, including small private key attacks\, factoring with known bits attacks\, etc. The talk will also discuss recent advancements in lattice-based cryptanalysis\, such as automated analysis and optimized attack bounds.
URL:https://www.greyc.fr/event/mengce-zheng-lattice-based-solving-strategy-using-coppersmiths-techniques-and-its-applications/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
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