Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

There are cryptographic processes that can produce unique "fingerprints" of messages that prove to the receiving party that the messages have not been altered. Some part of the message, such as the header text, is run through a one-way hashing function, which produces an output that serves as a unique identification for the message. The output is called a message digest. When a person receives such a message, they can run a similar hash function to create a message digest that should exactly match the digest sent with the message. If the digests do not match, the message should be considered invalid. This indicates message alteration, which changes the results of the hash and produces a different message digest.

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