Faster 2-regular information-set decoding

  • Authors:
  • Daniel J. Bernstein;Tanja Lange;Christiane Peters;Peter Schwabe

  • Affiliations:
  • Department of Computer Science, University of Illinois at Chicago, Chicago, IL;Department of Mathematics and Computer Science, Technische Universiteit Eindhoven, Eindhoven, The Netherlands;Department of Mathematics and Computer Science, Technische Universiteit Eindhoven, Eindhoven, The Netherlands;Institute of Information Science, Academia Sinica, Taipei, Taiwan

  • Venue:
  • IWCC'11 Proceedings of the Third international conference on Coding and cryptology
  • Year:
  • 2011

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Abstract

Fix positive integers B and w. Let C be a linear code over F2 of length Bw. The 2-regular-decoding problem is to find a nonzero code-word consisting of w length-B blocks, each of which has Hamming weight 0 or 2. This problem appears in attacks on the FSB (fast syndrome-based) hash function and related proposals. This problem differs from the usual information-set-decoding problems in that (1) the target code-word is required to have a very regular structure and (2) the target weight can be rather high, so that there are many possible codewords of that weight. Augot, Finiasz, and Sendrier, in the paper that introduced FSB, presented a variant of information-set decoding tuned for 2-regular decoding. This paper improves the Augot-Finiasz-Sendrier algorithm in a way that is analogous to Stern's improvement upon basic information-set decoding. The resulting algorithm achieves an exponential speedup over the previous algorithm.