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Seminar
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Cryptography
A Concrete Treatment of Efficient Continuous Group Key Agreement via Multi-Recipient PKEs
Speaker : Thomas Prest - PQShield
Continuous group key agreements (CGKAs) are a class of protocols that can provide strong security guarantees to secure group messaging protocols such as Signal and MLS. Protection against device compromise is provided by commit messages: at a regular rate, each group member may refresh their key material by uploading a commit message, which is then downloaded and processed by all the other members[…] -
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Seminar
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Cryptography
Middle-Product Learning with Rounding Problem and its Applications
Speaker : Katharina Boudgoust - Univ Rennes, CNRS, IRISA
This talk focuses on a new variant of the Learning With Errors (LWE) problem, a fundamental computational problem used in lattice-based cryptography.<br/> At Crypto17, Roşca et al. introduced the Middle-Product LWE problem (MP-LWE), whose hardness is based on the hardness of the Polynomial LWE (P-LWE) problem parameterized by a large set of polynomials, making it more secure against the possible[…] -
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Seminar
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Cryptography
Soutenance de thèse: Autour de la sécurité des messageries instantanées: des solutions pour des applications multi-appareils et les communications de groupe.
Speaker : Céline Duguey - DGA-Rennes
Les applications de messagerie instantanée sécurisée, telles WhatsApp ou Signal, sont devenues incontournables pour nos communications quotidiennes.<br/> Elles apportent une sécurité caractérisée notamment par le chiffrement de bout en bout, la confidentialité persistante ou encore la sécurité après compromission. Mais ces propriétés sont généralement limitées aux communications deux à deux. L[…] -
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Seminar
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Cryptography
Computing isogenies from modular equations in genus 2
Speaker : 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:[…] -
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Seminar
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Cryptography
Key recovery from partial information
Speaker : Gabrielle De Michelli - UC San Diego
The security of deployed protocols not only relies on the hardness of the underlying mathematical problem but also on the implementation of the algorithms involved. Many fast modular exponentiation algorithms have piled up over the years and some implementations have brought vulnerabilities that are exploitable by side-channel attacks, in particular cache attacks.<br/> In this talk, we consider[…] -
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Seminar
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Cryptography
Constant time implementation of rank based cryptography
Speaker : Nicolas Aragon - IRISA
Since the start of the NIST standardization project for post-quantum cryptography in 2017, rank metric based cryptography is becoming more popular as an alternative to code-based cryptography in the Hamming metric.<br/> While rank based cryptography has always been competitive in terms of keys and ciphertexts sizes, the lack of maturity in the implementations of these cryptosystems made them[…] -