Skein (hash function)

<h2 id="history">History</h2>
<p>Skein was created by <a href="/facts/Bruce_Schneier/kWxPFPmQ">Bruce Schneier</a>, <a href="/facts/Niels_Ferguson/hCX1IMQb">Niels Ferguson</a>, <a href="/facts/Stefan_Lucks/C8E8YPgn">Stefan Lucks</a>, Doug Whiting, <a href="/facts/Mihir_Bellare/uRjcPYqu">Mihir Bellare</a>, Tadayoshi Kohno, <a href="/facts/Jon_Callas/5DwK2DTU">Jon Callas</a> and Jesse Walker.
</p><p>Skein is based on the <a href="/facts/Threefish/xGnFbEtW">Threefish</a> <a href="/facts/Tweakable_block_cipher/MJywAyfQ">tweakable</a> <a href="/facts/Block_cipher/MJywAyfQ">block cipher</a> compressed using Unique Block Iteration (UBI) chaining mode, a variant of the <a href="/facts/Matyas%E2%80%93Meyer%E2%80%93Oseas/Rog6N1KR">Matyas–Meyer–Oseas</a> hash mode,<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> while leveraging an optional low-overhead argument-system for flexibility.
</p><p>Skein's algorithm and a <a href="/facts/Reference_implementation/k9B97xel">reference implementation</a> was given to <a href="/facts/Public_domain/YWKMDKw4">public domain</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h2 id="functionality">Functionality</h2>
<p>Skein supports internal state sizes of 256, 512 and 1024 bits, and arbitrary output sizes.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p><p>The authors claim 6.1 <a href="/facts/Cycles_per_byte/Dc39822I">cycles per byte</a> for any output size on an <a href="/facts/Intel_Core_2/9gJP9o8p">Intel Core 2</a> Duo in 64-bit mode.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>
</p><p>The core of Threefish is based on a MIX function that transforms 2 64-bit words using a single addition, rotation by a constant and XOR. The UBI chaining mode combines an input chaining value with an arbitrary length input string and produces a fixed size output.
</p><p>Threefish's <a href="/facts/Nonlinearity/4aYItALC">nonlinearity</a> comes entirely from the combination of addition operations and <a href="/facts/Exclusive_or/FHyr7hGQ">exclusive-ORs</a>; it does not use <a href="/facts/S-box/9xKgnLCF">S-boxes</a>.  The function is optimized for 64-bit processors, and the Skein paper defines optional features such as randomized <a href="/facts/Hash_function/rk6MlCt3">hashing</a>, <a href="/facts/Parallelizable/CQq7nQsJ">parallelizable</a> <a href="/facts/Merkle_tree/uGFY5mNA">tree hashing</a>, a <a href="/facts/Stream_cipher/BxU0aWmJ">stream cipher</a>, personalization, and a <a href="/facts/Key_derivation_function/3jL2jTTb">key derivation function</a>.
</p>
<h2 id="cryptanalysis">Cryptanalysis</h2>
<p>In October 2010, an attack that combines <a href="/facts/Rotational_cryptanalysis/9QXVCK9z">rotational cryptanalysis</a> with the <a href="/facts/Rebound_attack/Spny6WKz">rebound attack</a> was published. The attack finds rotational collisions for 53 of 72 rounds in Threefish-256, and 57 of 72 rounds in Threefish-512. It also affects the Skein hash function.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> This is a follow-up to the earlier attack published in February, which breaks 39 and 42 rounds respectively.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>
</p><p>The Skein team tweaked the <a href="/facts/Key_schedule/H2klHRyU">key schedule</a> constant for round 3 of the NIST hash function competition, to make this attack less effective, even though they believe the hash would still be secure without these tweaks.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
</p>
<h2 id="examples-of-skein-hashes">Examples of Skein hashes</h2>
<p>Hash values of empty string.
</p>
Skein-256-256("")
c8877087da56e072870daa843f176e9453115929094c3a40c463a196c29bf7ba
Skein-512-256("")
39ccc4554a8b31853b9de7a1fe638a24cce6b35a55f2431009e18780335d2621
Skein-512-512("")
bc5b4c50925519c290cc634277ae3d6257212395cba733bbad37a4af0fa06af41fca7903d06564fea7a2d3730dbdb80c1f85562dfcc070334ea4d1d9e72cba7a

<p>Even a small change in the message will (with overwhelming probability) result in a mostly different hash, due to the <a href="/facts/Avalanche_effect/hpYX5zu5">avalanche effect</a>. For example, adding a period to the end of the sentence:
</p>
Skein-512-256("<a href="/facts/The_quick_brown_fox_jumps_over_the_lazy_dog/LqNhzP4z">The quick brown fox jumps over the lazy dog</a>")
b3250457e05d3060b1a4bbc1428bc75a3f525ca389aeab96cfa34638d96e492a
Skein-512-256("<a href="/facts/The_quick_brown_fox_jumps_over_the_lazy_dog/LqNhzP4z">The quick brown fox jumps over the lazy dog</a>.")
41e829d7fca71c7d7154ed8fc8a069f274dd664ae0ed29d365d919f4e575eebb
Skein-512-512("<a href="/facts/The_quick_brown_fox_jumps_over_the_lazy_dog/LqNhzP4z">The quick brown fox jumps over the lazy dog</a>")
94c2ae036dba8783d0b3f7d6cc111ff810702f5c77707999be7e1c9486ff238a7044de734293147359b4ac7e1d09cd247c351d69826b78dcddd951f0ef912713
Skein-512-512("<a href="/facts/The_quick_brown_fox_jumps_over_the_lazy_dog/LqNhzP4z">The quick brown fox jumps over the lazy dog</a>.")
658223cb3d69b5e76e3588ca63feffba0dc2ead38a95d0650564f2a39da8e83fbb42c9d6ad9e03fbfde8a25a880357d457dbd6f74cbcb5e728979577dbce5436

<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.skein-hash.info/">Official Skein website</a> (dead, <a href="https://web.archive.org/web/20210401000151/http://www.skein-hash.info/">Wayback Machine archive</a>)</li>
<li><a href="https://www.schneier.com/skein.html">Bruce Schneier's Skein webpage</a></li></ul>
<h3>Implementations</h3>
<ul><li><a href="http://www.skein-hash.info/SPARKSkein-release">SPARKSkein</a> – an implementation of Skein in <a href="/facts/SPARK_(programming_language)/rQB6QTvf">SPARK</a>, with proofs of type-safety</li>
<li><a href="/facts/Botan_(programming_library)/IehRkvcn">Botan</a> contains a C++ implementation of Skein-512</li>
<li><a href="https://web.archive.org/web/20090913132131/http://www.sriramkrishnan.com/blog/2009/08/nskein-skein-implementation-net.html">nskein</a> – a .NET implementation of Skein with support for all block sizes</li>
<li><a href="http://packages.python.org/pyskein/">pyskein</a> Skein module for Python</li>
<li><a href="https://github.com/jedisct1/PHP-Skein-Hash">PHP-Skein-Hash</a> Skein hash for PHP on GitHub</li>
<li><a href="https://metacpan.org/module/Digest::Skein">Digest::Skein</a>, an implementation in C and Perl</li>
<li><a href="https://code.google.com/p/skeinfish/">skeinfish</a> A C# implementation of Skein and Threefish (based on version 1.3)</li>
<li><a href="http://www.h2database.com/skein/index.html">Java, Scala, and Javascript implementations of Skein 512-512 (based on version 1.3)</a></li>
<li><a href="https://web.archive.org/web/20081214181836/http://www.xs4all.nl/~warper/">A Java implementation of Skein (based on version 1.1)</a></li>
<li><a href="http://www.skein-hash.info/node/30">An implementation of Skein in Ada</a></li>
<li><a href="https://github.com/basho/skerl">skerl</a>, Skein hash function for Erlang, via NIFs</li>
<li><a href="http://sourceforge.net/p/skeinbash/home/Home/">Skein 512-512 implemented in Bash</a></li>
<li><a href="http://hackage.haskell.org/package/cryptohash">Skein implemented in Haskell</a></li>
<li><a href="http://cryptography.gmu.edu/athena/index.php?id=source_codes">VHDL source code</a> developed by the Cryptographic Engineering Research Group (CERG) at <a href="/facts/George_Mason_University/rWKeeMrh">George Mason University</a></li>
<li><a href="http://www.coderslagoon.com/#skeinr">skeinr</a> Skein implemented in Ruby</li>
<li><a href="http://www.syntax-k.de/projekte/fhreefish/">fhreefish</a> An efficient implementation of Skein-256 for 8-bit Atmel AVR microcontrollers, meeting the performance estimates outlined in the official specification</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"NIST Selects Winner of Secure Hash Algorithm (SHA-3) Competition". NIST. 2012-10-02. Retrieved 2012-10-02. <a href="https://www.nist.gov/itl/csd/sha-100212.cfm" target="_blank">https://www.nist.gov/itl/csd/sha-100212.cfm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Ferguson; et al. (2010-10-01). "The Skein Hash Function Family" (PDF). Archived from the original (PDF) on 2014-08-24. Retrieved 2010-12-15. {{cite journal}}: Cite journal requires |journal= (help) <a href="https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf" target="_blank">https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>http://www.skein-hash.info/sites/default/files/skein1.3.pdf Archived 2014-08-24 at the Wayback Machine p. 6 <a href="http://www.skein-hash.info/sites/default/files/skein1.3.pdf" target="_blank">http://www.skein-hash.info/sites/default/files/skein1.3.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>skein_NIST_CD_121508.zip Archived 2016-06-10 at the Wayback Machine on skein-hash.info, skein.c "Implementation of the Skein hash function. Source code author: Doug Whiting, 2008. This algorithm and source code is released to the public domain." <a href="http://www.skein-hash.info/sites/default/files/skein_NIST_CD_121508.zip" target="_blank">http://www.skein-hash.info/sites/default/files/skein_NIST_CD_121508.zip</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Now From Bruce Schneier, the Skein Hash Function". Slashdot. 2008-10-31. Retrieved 2008-10-31. <a href="http://it.slashdot.org/article.pl?sid=08/10/31/1426215" target="_blank">http://it.slashdot.org/article.pl?sid=08/10/31/1426215</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>"Paper describing the hash function, Version 1.3 (2010-10-01)" (PDF). Archived from the original (PDF) on 2014-08-24. Retrieved 2010-12-15. <a href="https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf" target="_blank">https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Dmitry Khovratovich; Ivica Nikolic; Christian Rechberger (2010-10-20). "Rotational Rebound Attacks on Reduced Skein". Cryptology ePrint Archive. <a href="http://eprint.iacr.org/2010/538" target="_blank">http://eprint.iacr.org/2010/538</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Dmitry Khovratovich & Ivica Nikolić (2010). "Rotational Cryptanalysis of ARX" (PDF). University of Luxembourg. Archived from the original (PDF) on 2013-01-26. Retrieved 2010-10-25. {{cite journal}}: Cite journal requires |journal= (help) <a href="https://web.archive.org/web/20130126083241/http://www.skein-hash.info/sites/default/files/axr.pdf" target="_blank">https://web.archive.org/web/20130126083241/http://www.skein-hash.info/sites/default/files/axr.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>Ferguson; et al. (2010-10-01). "The Skein Hash Function Family" (PDF). Archived from the original (PDF) on 2014-08-24. Retrieved 2010-12-15. {{cite journal}}: Cite journal requires |journal= (help) <a href="https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf" target="_blank">https://web.archive.org/web/20140824053109/http://www.skein-hash.info/sites/default/files/skein1.3.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
</ol>

Skein (hash function) open-in-new

Skein (hash function)