Year: 2019
Type: dissertation
Abstract: Lattice-based cryptography is a promising area for constructing cryptographic primitives that are plausibly secure even in the presence of quantum computers. A fundamental problem related to lattices is the shortest vector problem (or SVP), which asks to find a shortest non-zero vector in a lattice. This problem is believed to be intractable, even quantumly. Structured lattices, for example ideal lattices or module lattices (the latter being a generalization of the former), are often used to improve the efficiency of lattice-based primitives. The security of most of the schemes based on structured lattices is related to SVP in module lattices, and a very small number of schemes can also be impacted by SVP in ideal lattices.In this thesis, we first focus on the problem of finding short vectors in ideal and module lattices.We propose an algorithm which, after some exponential pre-computation, performs better on ideal lattices than the best known algorithm for arbitrary lattices. We also present an algorithm to find short vectors in rank 2 modules, provided that we have access to some oracle solving the closest vector problem in a fixed lattice. The exponential pre-processing time and the oracle call make these two algorithms unusable in practice.The main scheme whose security might be impacted by SVP in ideal lattices is the GGH13multilinear map. This protocol is mainly used today to construct program obfuscators, which should render the code of a program unintelligible, while preserving its functionality. In a second part of this thesis, we focus on the GGH13 map and its application to obfuscation. We first study the impact of statistical attacks on the GGH13 map and on its variants. We then study the security of obfuscators based on the GGH13 map and propose a quantum attack against multiple such obfuscators. This quantum attack uses as a subroutine an algorithm to find a short vector in an ideal lattice related to a secret element of the GGH13 map.
Author: Alice Pellet-Mary
Language: French
Subfield: Artificial Intelligence
Field: Computer Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2995933985
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