One way function

A one way function is a computable bijective function f with the following properties:

The computation of is tractable (which generally means that a polynomial algorithm for the computation is known, see complexity theory).

The computation of the inverse function is not tractable (i.e. no polynomial algorithm is known or exists).

An example of a one way function is the discrete logarithm.

One way functions are useful in cryptography, e.g. for digital signatures.