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Mathematics of Computation

Published by the American Mathematical Society since 1960 (published as Mathematical Tables and other Aids to Computation 1943-1959), Mathematics of Computation is devoted to research articles of the highest quality in computational mathematics.

ISSN 1088-6842 (online) ISSN 0025-5718 (print)

The 2020 MCQ for Mathematics of Computation is 1.78.

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Faster individual discrete logarithms in finite fields of composite extension degree
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by Aurore Guillevic HTML | PDF
Math. Comp. 88 (2019), 1273-1301 Request permission

Abstract:

Computing discrete logarithms in finite fields is a main concern in cryptography. The best algorithms in large and medium characteristic fields (e.g., $\rm {GF}(p^2)$, $\rm {GF}(p^{12})$) are the Number Field Sieve and its variants (special, high-degree, tower). The best algorithms in small characteristic finite fields (e.g., $\rm {GF}(3^{6 \cdot 509})$) are the Function Field Sieve, Joux’s algorithm, and the quasipolynomial-time algorithm. The last step of this family of algorithms is the individual logarithm computation. It computes a smooth decomposition of a given target in two phases: an initial splitting, then a descent tree. While new improvements have been made to reduce the complexity of the dominating relation collection and linear algebra steps, resulting in a smaller factor basis (database of known logarithms of small elements), the last step remains at the same level of difficulty. Indeed, we have to find a smooth decomposition of a typically large element in the finite field. This work improves the initial splitting phase and applies to any nonprime finite field. It is very efficient when the extension degree is composite. It exploits the proper subfields, resulting in a much more smooth decomposition of the target. This leads to a new trade-off between the initial splitting step and the descent step in small characteristic. Moreover it reduces the width and the height of the subsequent descent tree.
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Additional Information
  • Aurore Guillevic
  • Affiliation: Inria Nancy–Grand Est, Équipe Caramba, 615 rue du jardin botanique, CS 20101, 54603 Villers-lès-Nancy Cedex, France
  • MR Author ID: 963265
  • Email: aurore.guillevic@inria.fr
  • Received by editor(s): July 26, 2017
  • Received by editor(s) in revised form: February 26, 2018
  • Published electronically: September 6, 2018
  • © Copyright 2018 American Mathematical Society
  • Journal: Math. Comp. 88 (2019), 1273-1301
  • MSC (2010): Primary 11T71
  • DOI: https://doi.org/10.1090/mcom/3376
  • MathSciNet review: 3904147