Chapter

Advances in Cryptology – CRYPTO 2011

Volume 6841 of the series Lecture Notes in Computer Science pp 724-742

Inverting HFE Systems Is Quasi-Polynomial for All Fields

  • Jintai DingAffiliated withSouth China University of TechnologyDepartment of Mathematical Sciences, University of Cincinnati
  • , Timothy J. HodgesAffiliated withDepartment of Mathematical Sciences, University of Cincinnati

Abstract

In this paper, we present and prove the first closed formula bounding the degree of regularity of an HFE system over an arbitrary finite field. Though these bounds are not necessarily optimal, they can be used to deduce

  1. 1

    if D, the degree of the corresponding HFE polynomial, and q, the size of the corresponding finite field, are fixed, inverting HFE system is polynomial for all fields;

     
  2. 2

    if D is of the scale O(n α ) where n is the number of variables in an HFE system, and q is fixed, inverting HFE systems is quasi-polynomial for all fields.

     

We generalize and prove rigorously similar results by Granboulan, Joux and Stern in the case when q = 2 that were communicated at Crypto 2006.