La semaine de l’IMB

Updatable Encryption (UE) allows ciphertexts to be updated under new keys without decryption, enabling efficient key rotation. Constructing post-quantum UE with strong security guarantees is challenging: the only known CCA-secure scheme, COM-UE, uses bitwise encryption, resulting in large ciphertexts and high computational costs.

We introduce DINE, a CCA-secure, isogeny-based post-quantum UE scheme that is both compact and efficient. Each encryption, decryption, or update requires only a few power-of-2 isogeny computations in dimension 2 to encrypt 28B messages, yielding 320B ciphertexts and 224B update tokens at NIST security level 1---significantly smaller than prior constructions. Our full C implementation demonstrates practical performances: updates in 7ms, encryptions in 48ms, and decryptions in 86ms.

Our design builds on recent advances in isogeny-based cryptography, combining high-dimensional isogeny representations with the Deuring correspondence. We also introduce new algorithms for the Deuring correspondence which may be of independent interest. Moreover, the security of our scheme relies on new problems that might open interesting perspectives in isogeny-based cryptography.

preprint: https://eprint.iacr.org/2025/1853

https://www.maths-vives.fr/projet/climaths/

Dans la théorie de la géométrie de l'information développée par Amari, l'information de Fisher permet de définir une métrique riemannienne sur une famille paramétrique de distributions de probabilités donnée. Cette métrique permet de comparer et d'interpoler entre des distributions d'une même famille, et est caractérisée par son indépendance par rapport aux statistiques exhaustives. Amari introduit également une famille de connections affines avec cette même propriété. Dans cet exposé, nous parlerons de la généralisation de ces objets au cadre non paramétrique, et des structures géométriques induites sur l'espace des mesures de probabilités.

After a quick overview of the general principles of Life Cycle Assessment (LCA), we will investigate how such a tool can be helpful to compare the environmental impact of different architectures of computer systems used for teaching purposes in higher education. In particular, we will see how to perform the life cycle inventory of the systems under studies from a practical standpoint. We will then review the main results from the life cycle impact assessment and discuss them as well as the limitations of this study.

Voir ici : lien conférence

La conjecture de Littlewood P(t)-adique est une version sur les corps de fonctions de la conjecture du même nom (datant des années 1930) en approximation diophantienne. Elle a été proposée par De Mathan et Teulié en 2004. Nous la réfutons ici sur lorsque le corps de base est de caractéristique congruente à 3 modulo 4. 

Toutes les notions utiles seront introduites au cours de l'exposé. Travail en commun avec Dzmitry Badziahin (University of Sydney)

We study the Vehicle Routing Problem with Stochastic Demands (VRPSD), which involves optimizing delivery routes for vehicles with limited capacity to serve customers whose demands are unknown when designing the routes. The routes are designed taking into account the possibility that a route may have too much demand for the capacity of a vehicle to be delivered, in that case recourse actions can be taken, inducing a cost. This problem seeks to minimize routing costs and the expected recourse costs.

The Vehicle Routing Problem with Stochastic Demands is relevant as it addresses the need for efficient logistics under uncertainty in transportation and supply chain management. As a result, research on this problem is very active, and recent advances in exact resolution methods allow for tackling larger instances more efficiently and with greater generality regarding the different hypotheses surrounding recourse and uncertainty modeling.

In this talk, we present the state-of-the-art methods for solving the VRPSD. We first provide a definition of the problem and list its various components that can vary, such as recourse actions and different ways to model uncertainty. Then, we present different methods from the literature to solve the VRPSD, with a focus on the Disaggregated L-shaped method.