Paper 2010/282

Pseudo-Linear Approximations for ARX Ciphers: With Application to Threefish

Kerry A. McKay and Poorvi L. Vora

Abstract

The operations addition modulo 2^n and exclusive-or have recently been combined to obtain an efficient mechanism for nonlinearity in block cipher design. In this paper, we show that ciphers using this approach may be approximated by pseudo-linear expressions relating groups of contiguous bits of the round key, round input, and round output. The bias of an approximation can be large enough for known plaintext attacks. We demonstrate an application of this concept to a reduced-round version of the Threefish block cipher, a component of the Skein entry in the secure hash function competition.

Metadata
Available format(s)
PDF
Category
Secret-key cryptography
Publication info
Published elsewhere. Unknown where it was published
Keywords
ThreefishSkeinARX cipherlinear cryptanalysis
Contact author(s)
kerry @ gwu edu
History
2010-08-06: last of 3 revisions
2010-05-12: received
See all versions
Short URL
https://ia.cr/2010/282
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2010/282,
      author = {Kerry A.  McKay and Poorvi L.  Vora},
      title = {Pseudo-Linear Approximations for ARX Ciphers: With Application to Threefish},
      howpublished = {Cryptology ePrint Archive, Paper 2010/282},
      year = {2010},
      note = {\url{https://eprint.iacr.org/2010/282}},
      url = {https://eprint.iacr.org/2010/282}
}
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