Extending the GHS Weil Descent Attack

  • Steven D. Galbraith
  • Florian Hess
  • Nigel P. Smart
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 2332)


In this paper we extend the Weil descent attack due to Gaudry, Hess and Smart (GHS) to a much larger class of elliptic curves. This extended attack applies to fields of composite degree over F 2. The principle behind the extended attack is to use isogenies to find an elliptic curve for which the GHS attack is effective. The discrete logarithm problem on the target curve can be transformed into a discrete logarithm problem on the isogenous curve.

A further contribution of the paper is to give an improvement to an algorithm of Galbraith for constructing isogenies between elliptic curves, and this is of independent interest in elliptic curve cryptography. We show that a larger proportion than previously thought of elliptic curves over F 2155 should be considered weak.


Elliptic Curve Elliptic Curf Discrete Logarithm Endomorphism Ring Hyperelliptic Curve 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2002

Authors and Affiliations

  • Steven D. Galbraith
    • 1
  • Florian Hess
    • 2
  • Nigel P. Smart
    • 2
  1. 1.Mathematics DepartmentRoyal Holloway University of LondonEghamUK
  2. 2.Department of Computer ScienceUniversity of BristolBristolUK

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