Pseudorandom function family

A pseudo-random function is a family of efficiently computable functions that are virtually indistinguishable from a random oracle.

A family of functions is a mapping between nonempty finite quantities K, X, Y. For each key is given by a mapping. A random oracle is an algorithm that ( uniformly distributed ) returns for each input X of a randomly drawn from output Y, with the restriction that once a certain function value is fixed, ie with the same request, the same answer is given. Such a function family F is called pseudo- random if every efficient algorithm for a ( uniformly distributed ) random drawn and not known to him of k, between a random oracle and only negligible can distinguish better ( in k) than by installments.

From a cryptographically secure random number generator can be constructed by the method of Goldreich, Goldwasser and Micali a pseudo-random function.