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In cryptography, a pseudorandom function family, abbreviated PRF, is a collection of efficiently-computable functions which emulate a random oracle in the following way: no efficient algorithm can distinguish (with significant advantage) between a function chosen randomly from the PRF family and a random oracle (a function whose outputs are fixed completely at random). Pseudorandom functions are vital tools in the construction of cryptographic primitives, especially secure encryption schemes. Pseudorandom functions are not to be confused with pseudorandom generators (PRGs). The guarantee of a PRG is that a ''single'' output appears random if the input was chosen at random. On the other hand, the guarantee of a PRF is that ''all its outputs'' appear random, regardless of how the corresponding inputs were chosen, as long as the ''function'' was drawn at random from the PRF family. A pseudorandom function family can be constructed from any pseudorandom generator, using, for example, the "GGM" construction given by Goldreich, Goldwasser, and Micali.〔Oded Goldreich, Shafi Goldwasser, Silvio Micali (1986) "How to Construct Random Functions", ''Journal of the ACM'', vol.33, no.4, p.792-807. ; (preprint ); (web page and preprint )〕 ==Random functions== A PRF is an efficient (i.e. computable in polynomial time) deterministic function that maps two distinct sets (domain and range). Essentially a true random function would just be composed of a look-up table filled with random entries. However, in practice a PRF has only one input d (domain) and a hidden random seed (range) which when run multiple times with the same input, always outputs the same value. Nonetheless, given an arbitrary input the output looks random due to the random seed. A PRF is considered to be good if its behavior is indistinguishable from a true random function. Therefore, given a true random function and a PRF, there should be no efficient method of determining if the output was produced by a true random function or the PRF. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「pseudorandom function family」の詳細全文を読む スポンサード リンク
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