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. MD4 is also used to compute NT-hash password digests on Microsoft Windows NT, XP and Vista.
MD4 was designed to be fast, which meant taking a few risks regarding security. By 1992 weaknesses had been found which led Rivest to produce a strengthened, but slower, version known as MD5. In 1998, Dobbertin [1, 2] found the first MD4 collisions, and he gave an algorithm for generating such collisions, with a work factor that is approximately equal to the computation of 2^20 MD4 hashes.