Faster Multicollisions

  • Authors:
  • Jean-Philippe Aumasson

  • Affiliations:
  • FHNW, Windisch, Switzerland

  • Venue:
  • INDOCRYPT '08 Proceedings of the 9th International Conference on Cryptology in India: Progress in Cryptology
  • Year:
  • 2008

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Abstract

Joux’s multicollision attack is one of the most striking results on hash functions and also one of the simplest: it computes a kcollision on iterated hashes in time [log2 k&]·2n/2, whereas k!1/k ·2n(k−1)/k was thought to be optimal. Kelsey and Schneier improved this to 3 · 2n/2 if storage 2n/2 is available and if the compression functions admits easily found fixed-points. This paper presents a simple technique that reduces this cost to 2n/2 and negligible memory, when the IV can be chosen by the attacker. Additional benefits are shorter messages than the Kelsey/Schneier attack and cost-optimality.