A mathematical transformation of data of arbitrary length into a fixed-length string. The mathematical properties of the transformation ensure that the reversion of the hashing is computationally hard and that similar data yield dissimilar hashes. The output of a hash function—called a hash, message digest, or digital fingerprint—is used for authentication and message integrity purposes.
In cryptography, an algorithm that generates a fixed string of numbers from a text message. The "one-way" means that it is extremely difficult to turn the fixed string back into the text message. One-way hash functions are used for creating digital signatures for message and code authentication. See digital signature, MD5 and SHA.