International Conference on the Theory and Application of Cryptology and Information Security

ASIACRYPT 2009: Advances in Cryptology – ASIACRYPT 2009 pp 542-559

Improved Cryptanalysis of Skein

  • Jean-Philippe Aumasson
  • Çağdaş Çalık
  • Willi Meier
  • Onur Özen
  • Raphael C. -W. Phan
  • Kerem Varıcı
Conference paper

DOI: 10.1007/978-3-642-10366-7_32

Volume 5912 of the book series Lecture Notes in Computer Science (LNCS)
Cite this paper as:
Aumasson JP., Çalık Ç., Meier W., Özen O., Phan R.C.W., Varıcı K. (2009) Improved Cryptanalysis of Skein. In: Matsui M. (eds) Advances in Cryptology – ASIACRYPT 2009. ASIACRYPT 2009. Lecture Notes in Computer Science, vol 5912. Springer, Berlin, Heidelberg

Abstract

The hash function Skein is the submission of Ferguson et al. to the NIST Hash Competition, and is arguably a serious candidate for selection as SHA-3. This paper presents the first third-party analysis of Skein, with an extensive study of its main component: the block cipher Threefish. We notably investigate near collisions, distinguishers, impossible differentials, key recovery using related-key differential and boomerang attacks. In particular, we present near collisions on up to 17 rounds, an impossible differential on 21 rounds, a related-key boomerang distinguisher on 34 rounds, a known-related-key boomerang distinguisher on 35 rounds, and key recovery attacks on up to 32 rounds, out of 72 in total for Threefish-512. None of our attacks directly extends to the full Skein hash. However, the pseudorandomness of Threefish is required to validate the security proofs on Skein, and our results conclude that at least 36 rounds of Threefish seem required for optimal security guarantees.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2009

Authors and Affiliations

  • Jean-Philippe Aumasson
    • 1
  • Çağdaş Çalık
    • 2
  • Willi Meier
    • 1
  • Onur Özen
    • 3
  • Raphael C. -W. Phan
    • 4
  • Kerem Varıcı
    • 5
  1. 1.FHNWWindischSwitzerland
  2. 2.Institute of Applied MathematicsMiddle East Technical UniversityAnkaraTurkey
  3. 3.EPFL IC LACALLausanneSwitzerland
  4. 4.Electronic and Electrical EngineeringLoughborough UniUK
  5. 5.Dept. of Electrical EngineeringK.U.LeuvenHeverleeBelgium