Title

The Number Field Sieve For Integers Of Low Weight

Abstract

We define the weight of an integer N to be the smallest w such that N can be represented as E-i=1(w) epsilon(i)2(ci), with epsilon(i), ... , epsilon(w) is an element of {1, -1}. Since arithmetic modulo a prime of low weight is particularly efficient, it is tempting to use such primes in cryptographic protocols. In this paper we consider the difficulty of the discrete logarithm problem modulo a prime N of low weight, as well as the difficulty of factoring an integer N of low weight. We describe a version of the number field sieve which handles both problems. In the case that w = 2, the method is the same as the special number field sieve, which runs conjecturally in time exp(((32/9)(1/3) + o(1))(log N)(1/3)(log log N)(2/3)) for N -> infinity. For fixed w > 2, we conjecture that there is a constant xi less than (32/9)(1/3)((2w - 3)/(w - 1))(1/3) such that the running time of the algorithm is at most exp((xi + o(1))(log N)(1/3)(log log N)(2/3)) for N -> infinity. We further conjecture that no xi less than (32/9)(1/3)((root 2w - 2 root 2 + 1)/(w - 1))(2/3) has this property. Our analysis reveals that on average the method performs significantly better than it does in the worst case. We consider all the examples given in a recent paper of Koblitz and Menezes and demonstrate that in every case but one, our algorithm runs faster than the standard versions of the number field sieve.

Publisher

American Mathematical Society

Publication Date

1-1-2010

Publication Title

Mathematics Of Computation

Department

Mathematics

Document Type

Article

DOI

10.1090/S0025-5718-09-02198-X

Keywords

Discrete logarithm, Integer factorization, Number field sieve, Mathematics, applied

Language

English

Format

text

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