Message Digest Algorithms
Message Digest algorithms produce a “digest” or cryptographic residue from any message (file). Regardless of the size of the message, the output is a short 128 to 512 bit binary value (depending on Message Digest Algorithm) that “characterizes” the message. Message Digest algorithms do not use keys. A given message (with a given Message Digest algorithm) will always produce exactly the same digest. Any change at all in a message (even a single bit in a 10MB message) will produce a completely different digest.