Cryptographic Hash
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Cryptographic Hash

A hash function is an algorithm that maps a large data object (usually of a variable size) onto a small data object of fixed size. Cryptographic hash functions are used to produce a message digest which is an integral part of secure e-mail. They generate a checksum for the message, thus affirming or denying the integrity of the message itself.

Alice sends a message to Bob and attaches a message digest containing the hash result for the message. Bob computes a new hash result from the received message and compares it with the received hash result. If they are identical, Bob knows that the message received is exactly the same as the message sent; that is, it has not been altered in any way. If the two hash results are different, then Bob knows that the message from Alice has been compromised.

A cryptographic hash function has a number of specific attributes:

* it must be 'one-way'; that is, it must be computationally infeasible to generate the input (the original message) from the hash result
* it must be collision free