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Message Digest 5 (MD5) is a hash function used in cryptography. Developed by Ronald Rivest in 1991, Message Digest 5 produces a 128-bit resulting hash value. Similar to other message-digest algorithms, it was largely developed for digital signature applications which make use of a large compressed file in a secure fashion.
Although it is still widely used, security of the function is severely compromised and as a result most applications, especially ones related to the U.S. government, require the SHA-2 family of hash functions for cryptography. Message Digest 5 is considered to be broken and unsuitable for further use according to the U.S. Department of Homeland Security.
Details of the Message Digest 5 algorithm are provided in RFC 1321. The algorithm of Message Digest 5 makes use of a message of any length and outputs a 128-bit message digest of the input. The Message Digest 5 algorithm does not need any large substitution tables and is an extension of the Message Digest 4 algorithm. Compared to Message Digest 4, Message Digest 5 is more conservative in design but is slower. The steps involved in the Message Digest 5 algorithm are appending of padding bits, appending representation of padded message to the original message, initialization of message digest buffer, processing of message in 16-word blocks and finally outputting the result. Compared to Message Digest 4, Message Digest 5 is slightly more complex.
On a 32-bit machine, Message Digest 5 performs much faster compared to other message digest algorithms. Message Digest 5 is simple to implement when compared with similar digest algorithms. The difficulty of coming up with same message digest from two different messages are on the order of 264 operations.