An improved algebraic attack on Hamsi-256

Itai Dinur, Adi Shamir

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations


Hamsi is one of the 14 second-stage candidates in NIST's SHA-3 competition. The only previous attack on this hash function was a very marginal attack on its 256-bit version published by Thomas Fuhr at Asiacrypt 2010, which is better than generic attacks only for very short messages of fewer than 100 32-bit blocks, and is only 26 times faster than a straightforward exhaustive search attack. In this paper we describe a different algebraic attack which is less marginal: It is better than the best known generic attack for all practical message sizes (up to 4 gigabytes), and it outperforms exhaustive search by a factor of at least 512. The attack is based on the observation that in order to discard a possible second preimage, it suffices to show that one of its hashed output bits is wrong. Since the output bits of the compression function of Hamsi-256 can be described by low degree polynomials, it is actually faster to compute a small number of output bits by a fast polynomial evaluation technique rather than via the official algorithm.

Original languageEnglish
Title of host publicationFast Software Encryption - 18th International Workshop, FSE 2011, Revised Selected Papers
Number of pages19
StatePublished - 11 Jul 2011
Externally publishedYes
Event18th International Workshop on Fast Software Encryption, FSE 2011 - Lyngby, Denmark
Duration: 13 Feb 201116 Feb 2011

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume6733 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference18th International Workshop on Fast Software Encryption, FSE 2011


  • Algebraic attacks
  • Hamsi
  • hash functions
  • second preimages

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Computer Science (all)


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