[Resource Topic] 2011/598: New Subexponential Algorithms for Factoring in $SL(2,\fq)$

Welcome to the resource topic for 2011/598

Title:
New Subexponential Algorithms for Factoring in SL(2,\fq)

Authors: Jean-Charles Faugère, Ludovic Perret, Christophe Petit, Guénaël Renault

Abstract:

Cayley hash functions are a particular kind of cryptographic hash functions with very appealing properties. Unfortunately, their security is related to a mathematical problem whose hardness is not very well understood, the {factorization problem in finite groups}. Given a group G, a set of generators \gen for this group and an element g\in G, the factorization problem asks for a ``short’’ representation of g as a product of the generators. In this paper, we provide a new algorithm for solving this problem for the group G:=\G. We first reduce the problem to the resolution of a particular kind of multivariate equation over \fq. Then, we introduce a dedicated approach to solve this equation with Gröbner bases. We provide a complexity analysis of our approach that is of independent interest from the point of view of Gröbner basis algorithms. Finally, we give the first subexponential time algorithm computing polynomial-length factorizations of any element g with respect to any generator set \gen of \G. Previous algorithms only worked for specific generator sets, ran in exponential time or produced factorizations that had at least a subexponential length. In practice, our algorithm beats the birthday-bound complexity of previous attacks for medium and large values of n.

ePrint: https://eprint.iacr.org/2011/598

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