Mélissa Rossi works as a cryptography expert in the French cybersecurity agency (ANSSI). She recently obtained her PhD from the Ecole Normale Supérieure (ENS) of Paris with an industrial funding from Thales and a partneship with ANSSI. Her subject was entitled « Extended Security of Lattice-based Cryptography ». Before that, she received a master’s degree in theoretical computer science from University Paris-Saclay and a master of science in engineering from Telecom Paristech.

Title of talk: Assessing residual security of lattice-based cryptography

Abstract: This talk will present a framework for cryptanalysis of lattice-based schemes, when side information —in the form of « hints »— about the secret is available. This presentation outlines a joint work with Dana Dachman-Soled, Léo Ducas and Huijing Gong that was presented in CRYPTO 2020 (https://eprint.iacr.org/2020/292).

This framework generalizes the primal lattice reduction attack, and allows the progressive integration of hints before running a final lattice reduction step. The techniques for integrating hints include sparsifying the lattice, projecting onto and intersecting with hyperplanes, and/or altering the distribution of the secret vector. The main contribution is to propose a toolbox and a methodology to integrate such hints into lattice reduction attacks and to predict the performance of those lattice attacks with side information.

While initially designed for side-channel information, this framework can also be used in other cases. For example, one can simply exploit constraints imposed by certain schemes (LAC, Round5, NTRU). Besides, I will present a way to use this framework combined with decryption failures information using a joint work with Jan-Pieter D’Anvers and Fernando Virdia presented in EUROCRYPT 2020 (https://eprint.iacr.org/2019/1399).