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| | Cryptographic hash function - Wikipedia, the free encyclopedia |
 | | A message authentication code or MAC takes a message and a secret key and generates a "MAC tag", such that it is difficult for an attacker to generate a valid (message, tag) pair that doesn't match one they've already seen; they are used to prevent attackers forging messages, among other uses. |
 | | Determination of whether or not any changes have been made to a message (or a file), for example, can be accomplished by comparing message digests calculated before, and after, transmission (or any other event) (see Tripwire, a system using this property as a defense against malware and malfeasance). |
 | | Bits representing the length of the entire message are appended to the message and padded suitably as part of the last block. |
| en.wikipedia.org /wiki/Message_digest (1431 words) |
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