MD4


The MD4 Message-Digest Algorithm is a cryptographic hash function developed by Ronald Rivest in 1990. The digest length is 128 bits. The algorithm has influenced later designs, such as the MD5, SHA-1 and RIPEMD algorithms. The initialism "MD" stands for "Message Digest."
The security of MD4 has been severely compromised. The first full collision attack against MD4 was published in 1995 and several newer attacks have been published since then. As of 2007, an attack can generate collisions in less than 2 MD4 hash operations. A theoretical preimage attack also exists.
A variant of MD4 is used in the to provide a unique identifier for a file in the popular eDonkey2000 / eMule P2P networks. MD4 was also used by the rsync protocol
MD4 is used to compute NTLM password-derived key digests on Microsoft Windows NT, XP, Vista, 7, 8, and 10.

Security

Weaknesses in MD4 were demonstrated by Den Boer and Bosselaers in a paper published in 1991. The first full-round MD4 collision attack was found by Hans Dobbertin in 1995, which took only seconds to carry out at that time. In August 2004, Wang et al. found a very efficient collision attack, alongside attacks on later hash function designs in the MD4/MD5/SHA-1/RIPEMD family. This result was improved later by Sasaki et al., and generating a collision is now as cheap as verifying it.
In 2008, the preimage resistance of MD4 was also broken by Gaëtan Leurent, with a 2102 attack.. In 2010 Guo et al published a 299.7 attack.
In 2011, RFC 6150 stated that RFC 1320 is historic.

MD4 hashes

The 128-bit MD4 hashes are typically represented as 32-digit hexadecimal numbers. The following demonstrates a 43-byte ASCII input and the corresponding MD4 hash:
MD4
= 1bee69a46ba811185c194762abaeae90
Even a small change in the message will result in a completely different hash, e.g. changing d to c:
MD4
= b86e130ce7028da59e672d56ad0113df
The hash of the zero-length string is:
MD4 = 31d6cfe0d16ae931b73c59d7e0c089c0

MD4 test vectors

The following test vectors are defined in RFC 1320
MD4 = 31d6cfe0d16ae931b73c59d7e0c089c0
MD4 = bde52cb31de33e46245e05fbdbd6fb24
MD4 = a448017aaf21d8525fc10ae87aa6729d
MD4 = d9130a8164549fe818874806e1c7014b
MD4 = d79e1c308aa5bbcdeea8ed63df412da9
MD4 = 043f8582f241db351ce627e153e7f0e4
MD4 = e33b4ddc9c38f2199c3e7b164fcc0536

MD4 collision example

Let:
k1 = 839c7a4d7a92cb678a5d59eea5a7573c8a74deb366c3dc20a083b69f5d2a3bb3719dc69891e9f95e809fd7e8b23ba6318ed45e51fe39708bf9427e9c3e8b9
k2 = 839c7a4d7a92cb678a5d59eea5a7573c8a74deb366c3dc20a083b69f5d2a3bb3719dc69891e9f95e809fd7e8b23ba6318ed45e51fe39708bf9427e9c3e8b9
k1 ≠ k2, but MD4 = MD4 = 4d7e6a1defa93d2dde05b45d864c429b
Note that two hex-digits of k1 and k2 define one byte of the input string, whose length is 64 bytes.

Collision attacks