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MD4 is a message digest algorithm (the fourth in a series) designed by Professor Ronald Rivest of MIT in 1990. It implements a cryptographic hash function for use in message integrity checks. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA and RIPEMD algorithms.

Weaknesses in MD4 were demonstrated by Den Boer and Bosselaers in a paper published in 1991. In August 2004, researchers reported generating collisions in MD4 using "hand calculation" (collision attack, not preimage attack), alongside attacks on later hash function designs in the MD4/MD5/SHA/RIPEMD family. The average runtime for a collision attack is 5 seconds on a modern computer (ref: http://stachliu.com/research_collisions.html ).

A variant of MD4 is used in the ed2k URI scheme to provide a unique indentifier for a file in the popular eDonkey2000 / eMule P2P networks.

MD4 hashes

The 128-bit (16-byte) MD4 hashes (also termed message digests) are typically represented as 32-digit hexadecimal numbers. The following demonstrates a 43-byte ASCII input and the corresponding MD4 hash:

MD4("The quick brown fox jumps over the lazy dog") 
 = 1bee69a46ba811185c194762abaeae90

Even a small change in the message will (with overwhelming probability) result in a completely different hash, e.g. changing d to c:

MD4("The quick brown fox jumps over the lazy cog") 
 = b86e130ce7028da59e672d56ad0113df

The hash of the zero-length string is:

MD4("") = 31d6cfe0d16ae931b73c59d7e0c089c0

See also

• MD2
• MD5

References

• Hans Dobbertin, 1998. Cryptanalysis of MD4. J. Cryptology 11(4): 253–271
• Hans Dobbertin: Cryptanalysis of MD4. Fast Software Encryption 1996: 53–69

External links

• Using Lepton's crack to break a MD4 hash password
• RFC 1320 - Description of MD4 by Ron Rivest
• An Attack on the Last Two Rounds of MD4
• A collision attack on MD4 (Presented at Eurocrypt 2005. Requires about ${\displaystyle 2^{14}}$ MD4 computations. Demonstrates "Theoretical Pre-image Attack on MD4" and "Second Pre-Image Attack for Weak Messages".)
• On the Security of Encryption Modes of MD4, MD5 and HAVAL ("MD4 can be broken by related-key boomerang attacks in real time. The attacks have been experimentally tested and run in milliseconds on a PC.")
• Improved Collision Attack on MD4 ("We were able to find collisions with probability almost 1, and the average complexity to find a collision is upper bounded by three times of MD4 hash operations.")
• Paj's Home: Cryptography — by Paj in JavaScript. Also supports MD5, and SHA-1. Released under the BSD License. Contains links to several other implementations.
• MD4 PHP Implementation — based on Paj's JavaScript implementation.

Collisions

• Fast MD4 Collision Generator

• Cryptographic hash functions