Skein

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Skein
Skein
developer Bruce Schneier, Stefan Lucks, Niels Ferguson, Doug Whiting, Mihir Bellare, Tadayoshi Kohno, Jon Callas, Jesse Walker
Released October 2010 (Version 1.3)
Derived from Block cipher Threefish
Certification SHA-3 finalist
Length of the hash value (bit) variable, 256 and 512 are common
construction Unique block iteration,
similar to HAIFA construction
Round 72

Skein (English for " strand ") is a family of cryptographic hash functions and was developed by Niels Ferguson , Stefan Lucks, Bruce Schneier , Doug Whiting, Mihir Bellare , Tadayoshi Kohno, Jon Callas and Jesse Walker. Skein was a contestant for the future SHA-3 standard , in which he reached the finalist round in December 2010.

construction

The Unique Block Iteration (UBI) construction method was developed especially for Skein, replacing the Merkle-Damgård construction that was used previously . UBI works in a similar way to the HAIFA construction . The message is expanded and divided into blocks that are processed one after the other. Each message block is entered into a compression function together with a linkage value and some administrative data, including a counter for the message bits that have already been processed, which supplies the next linkage value. The last concatenation value is finalized by another call to the compression function, which results in the hash value.

Skein uses a Matyas – Meyer – Oseas compression function based on the Threefish block encryption . The message block is entered as plain text and the concatenation value with the administration data as a key / tweak. The next concatenation value is created by XORing plain text and ciphertext. Threefish encrypts in 72 rounds with a block size of 256 or 512 bits. For the block size 1024 bits, 80 rounds are used.

The design is optimized to achieve high performance on 64-bit processors . With a block size of 512 bits, the computing effort on an Intel Core 2 Duo is around 6 cycles per byte.

weaknesses

At the second SHA-3 conference, Dmitry Khovratovich, Ivica Nikolié and Christian Rechberger showed a possible weakness in threefish and the compression function of skein. The authors then adjusted the algorithm slightly.

Web links

Individual evidence

  1. ↑ Ferguson et al .: The Skein Hash Function Family , October 1, 2010, online (PDF; 479 kB)
  2. ↑ http://csrc.nist.gov/groups/ST/hash/sha-3/Round2/Aug2010/documents/papers/RECHBERGER_rot-rebound.pdf
  3. ↑ http://www.schneier.com/blog/archives/2010/09/more_skein_news.html