MD4 Explanation

(Source from Wikipedia.org)

MD4 (Message-Digest algorithm 4) 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. MD4 is also used to compute NT-hash password digests on Microsoft Windows NT, XP, Vista and 7^{[citation needed]}.

One MD4 operation : MD4 consists of 48 of these operations, grouped in three rounds of 16 operations. F is a nonlinear function; one function is used in each round. M_i denotes a 32-bit block of the message input, and K_i denotes a 32-bit constant, different for each operation.

Weaknesses in MD4 were demonstrated by Den Boer and Bosselaers in a paper published in 1991. The first collision attack was found by Hans Dobbertin in 1996. In August 2004, Wang et al. found a very efficient collision attack, alongside attacks on later hash function designs in the MD4/MD5/SHA/RIPEMD family. This result was improved later by Sasaki et al., and generating a collision is now as cheap as verifying it (a few microseconds).
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 is also used by the rsync protocol.