On the function field sieve and the impact of higher splitting probabilities: Application to discrete logarithms in double-struck F 21971 and double-struck F23164

Abstract

In this paper we propose a binary field variant of the Joux-Lercier medium-sized Function Field Sieve, which results not only in complexities as low as Lqn(1/3,(4/9)1/3) for computing arbitrary logarithms, but also in an heuristic polynomial time algorithm for finding the discrete logarithms of degree one and two elements when the field has a subfield of an appropriate size. To illustrate the efficiency of the method, we have successfully solved the DLP in the finite fields with 21971 and 23164 elements, setting a record for binary fields. © 2013 International Association for Cryptologic Research.