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DesignersRonald Rivest, Benjamin Agre, Dan Bailey, Sarah Cheng, Christopher Crutchfield, Yevgeniy Dodis, Kermin Fleming, Asif Khan, Jayant Krishnamurthy, Yuncheng Lin, Leo Reyzin, Emily Shen, Jim Sukha, Eran Tromer, Yiqun Lisa Yin
First published2008
SeriesMD2, MD4, MD5, MD6
Digest sizesVariable, 0<d≤512 bits
StructureMerkle tree
RoundsVariable. Default, Unkeyed=40+[d/4], Keyed=max(80,40+(d/4)) [1]
Best public cryptanalysis
Key-recovery attack of a 14-round MD6 function in 222 operations.[2]

The MD6 Message-Digest Algorithm is a cryptographic hash function. It uses a Merkle tree-like structure to allow for immense parallel computation of hashes for very long inputs. Authors claim a performance of 28 cycles per byte for MD6-256 on an Intel Core 2 Duo and provable resistance against differential cryptanalysis.[3] The source code of the reference implementation was released under MIT license.[4]

Speeds in excess of 1 GB/s have been reported to be possible for long messages on 16-core CPU architecture.[1]

In December 2008, Douglas Held of Fortify Software discovered a buffer overflow in the original MD6 hash algorithm's reference implementation. This error was later made public by Ron Rivest on 19 February 2009, with a release of a corrected reference implementation in advance of the Fortify Report.[5]

MD6 was submitted to the NIST SHA-3 competition. However, on July 1, 2009, Rivest posted a comment at NIST that MD6 is not yet ready to be a candidate for SHA-3 because of speed issues, a "gap in the proof that the submitted version of MD6 is resistant to differential attacks", and an inability to supply such a proof for a faster reduced-round version,[6] although Rivest also stated at the MD6 website that it is not withdrawn formally.[7] MD6 did not advance to the second round of the SHA-3 competition. In September 2011, a paper presenting an improved proof that MD6 and faster reduced-round versions are resistant to differential attacks[8] was posted to the MD6 website.[9]

See also[edit]


  1. ^ a b Ronald L. Rivest; et al. "The MD6 Hash Function" (PDF). Archived from the original (PDF) on 2017-08-12. Retrieved 2024-01-29.
  2. ^ Aumasson, Jean-Philippe; Dinur, Itai; Meier, Willi; Shamir, Adi (2009). "Cube Testers and Key Recovery Attacks on Reduced-Round MD6 and Trivium". Fast Software Encryption. Vol. 5665. Berlin, Heidelberg: Springer Berlin Heidelberg. p. 1–22. doi:10.1007/978-3-642-03317-9_1. ISBN 978-3-642-03316-2.
  3. ^ Ronald L. Rivest. "The MD6 hash function A proposal to NIST for SHA-3". Archived from the original on 2020-11-09. Retrieved 2008-10-07. (Microsoft PowerPoint file)
  4. ^ readme.txt
  5. ^ "Fortify-SHA-3-Report" (PDF). Archived from the original (PDF) on 2012-02-22.
  6. ^ Rivest, Ronald (July 1, 2009). "OFFICIAL COMMENT: MD6". Retrieved September 27, 2011.
  7. ^ Schneier, Bruce (July 1, 2009). "MD6 Withdrawn from SHA-3 Competition". Retrieved July 9, 2009.
  8. ^ Heilman, Ethan (July 10, 2011). "Restoring the Differential Resistance of MD6". Retrieved September 27, 2011.
  9. ^ Heilman, Ethan (September 2011). "Improved Differential Analysis". Retrieved September 27, 2011.

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