523 résultats
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Cryptanalysis of code-based cryptosystems using the square-code distinguisher
Orateur : Mathieu Lequesne - INRIA
Many code-based cryptosystems have been proposed recently, especially in response to the call for post-quantum cryptography standardization issued by the National Institute of Standards and Technologie. Most code-based cryptosystem rely on the same idea: an error-correcting code with some special structural properties (including good error-correction capacity) serves as the private key. This code[…] -
Constant time techniques for lattice based cryptography
Orateur : Melissa Rossi - École normale supérieure, CNRS, PSL University, Inria
NIST’s post-quantum cryptography competition has entered in its second phase, the time has come to focus more closely on practical aspects of the candidates. On the lattice-based side, certain schemes chose to implement discrete Gaussian distributions which allow better parameters and security reductions. However, this advantage has also proved to be their Achilles’ heel, as discrete Gaussians[…] -
The Revival of Quadratic Fields Cryptography
Orateur : Guilhem Castagnos - Université Bordeaux 1
More than 30 years ago, Buchmann and Williams proposed using ideal class groups of imaginary quadratic fields in cryptography with a Diffie-Hellman style key exchange protocol. After several twists, there has been in recent years a new interest in this area. This rebirth is mainly due to two features. First, class groups of imaginary quadratic fields allow the design of cryptographic protocols[…] -
Computing isogenies from modular equations in genus 2
Orateur : Jean Kieffer - Université Bordeaux 1
Given two l-isogenous elliptic curves, a well-known algorithm of Elkies uses modular polynomials to compute this isogeny explicitly. In this work, we generalize his ideas to Jacobians of genus 2 curves. Our algorithms works for both l-isogenies and (in the RM case) cyclic isogenies, and uses Siegel or Hilbert type modular equations respectively. This has applications for point counting in genus 2:[…] -
Divisible E-Cash from Constrained Pseudo-Random Functions
Orateur : Olivier Sanders - Orange
Electronic cash (e-cash) is the digital analogue of regular cash which aims at preserving users' privacy. Following Chaum's seminal work, several new features were proposed for e-cash to address the practical issues of the original primitive. Among them, divisibility has proved very useful to enable efficient storage and spendings. Unfortunately, it is also very difficult to achieve and, to date,[…] -
Lattice-based signatures: from construction to implementation
Orateur : Pauline Bert - soutenance de thèse, amphi P de l'ISTIC, 14h
Lattice-based cryptography is one of the major line of research to build post-quantum public key primitives. In this thesis, we discuss about digital signatures constructions and their implementation. We first describe a Fiat-Shamir transformation from an identification scheme using rejection sampling to a digital signature secure in the random oracle model. Then we describe an identity-based[…]