International Association for Cryptologic Research (IACR)
Doi
Abstract
The selection of polynomials to represent number fields crucially determines the efficiency of the Number Field Sieve
(NFS) algorithm for solving the discrete logarithm in a finite field. An important recent work due to Barbulescu et al. builds upon
existing works to propose two new methods for polynomial selection when the target field is a non-prime field. These methods are
called the generalised Joux-Lercier (GJL) and the Conjugation methods. In this work, we propose a new method (which we denote
as A) for polynomial selection for the NFS algorithm in fields FQ, with Q=pn and n>1.
The new method both subsumes and generalises the GJL and the Conjugation methods and provides new trade-offs for both n composite
and n prime. Let us denote the variant of the (multiple) NFS algorithm using the polynomial selection method ``{X} by (M)NFS-{X}.
Asymptotic analysis is performed for both the NFS-A and the MNFS-A algorithms.
In particular, when p=LQ(2/3,cp), for cp∈[3.39,20.91], the complexity of NFS-A is better than the complexities
of all previous algorithms whether classical or MNFS. The MNFS-A algorithm provides lower complexity compared to
NFS-A algorithm; for cp∈(0,1.12]∪[1.45,3.15], the complexity of MNFS-A
is the same as that of the MNFS-Conjugation and for cp∈/(0,1.12]∪[1.45,3.15], the complexity of MNFS-A
is lower than that of all previous methods