MD4 and MD5 are the initial members of the MD4 type hash functions. Both were designed by Rivest [1, 2]. They take variable length input messages and hash them to fixed-length outputs. Both operate on 512-bit message blocks divided into 32-bit words and produce a message digest of 128 bits. First, the message is padded according to the so-called Merkle-Damgård strengthening technique (see hash functionsfor more details). Next, the message is processed block by block by the underlying compression function. This function initializes four 32-bit chaining variables to a fixed value prior to hashing the first message block, and to the current hash value for the following message blocks. Each step of the compression function updates in turn one of the chaining variables according to one message word. Both compression functions are organised into rounds of 16 steps each. MD4 has three such rounds, while MD5 consists of 4 rounds. In each round every message word is used just once in updating...
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Bosselaers, A. (2005). Md4-Md5. In: van Tilborg, H.C.A. (eds) Encyclopedia of Cryptography and Security. Springer, Boston, MA . https://doi.org/10.1007/0-387-23483-7_249
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