In [[cryptography]], a '''one-way compression function''' is a function that transforms atwo fixed-length inputinputs into a fixed-length output.<ref>Handbook of Applied Cryptography by Alfred J. Menezes, Paul C. van Oorschot, Scott A. Vanstone. Fifth Printing (August 2001) page 328.</ref> The transformation is [[one-way function|"one-way"]], meaning that it is difficult given a particular output to compute inputs which compress to that output. One-way compression functions are not related to [[data compression]], which by definition can be inverted exactly (lossless compression) or approximately (lossy compression) to the original data.
