Oracle-Assisted Static Diffie-Hellman Is Easier Than Discrete Logarithms

  • Authors:
  • Antoine Joux;Reynald Lercier;David Naccache;Emmanuel Thomé

  • Affiliations:
  • DGA and Université de Versailles, UVSQ PRISM, Versailles CEDEX, France F-78035;DGA/CELAR, La Roche Marguerite, F-35174 Bruz, France and, IRMAR, Université de Rennes 1, Rennes, France F-35042;École normale supérieure, Équipe de cryptographie, Paris CEDEX 05, France F-75230;LORIA, CACAO --- bâtiment A, INRIA Lorraine, Villiers-lès-Nancy CEDEX, France F-54602

  • Venue:
  • Cryptography and Coding '09 Proceedings of the 12th IMA International Conference on Cryptography and Coding
  • Year:
  • 2009

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Abstract

This paper extends Joux-Naccache-Thomé's e -th root algorithm to the static Diffie-Hellman problem (sdhp ). The new algorithm can be adapted to diverse finite fields by customizing it with an nfs -like core or an ffs -like core. In both cases, after a number of non-adaptive sdhp oracle queries, the attacker builds-up the ability to solve new sdhp instances unknown before the query phase . While sub-exponential, the algorithm is still significantly faster than all currently known dlp and sdhp resolution methods. We explore the applicability of the technique to various cryptosystems.The attacks were implemented in ${\mathbb F}_{2^{1025}}$ and also in ${\mathbb F}_{p}$, for a 516-bit p .