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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク pseudorandom generator ： ウィキペディア英語版 pseudorandom generator In theoretical computer science and cryptography, a pseudorandom generator (PRG) for a class of statistical tests is a deterministic procedure that maps a random seed to a longer pseudorandom string such that no statistical test in the class can distinguish between the output of the generator and the uniform distribution. The random seed is typically a short binary string drawn from the uniform distribution. Many different classes of statistical tests have been considered in the literature, among them the class of all Boolean circuits of a given size. It is not known whether good pseudorandom generators for this class exist, but it is known that their existence is in a certain sense equivalent to (unproven) circuit lower bounds in computational complexity theory. Hence the construction of pseudorandom generators for the class of Boolean circuits of a given size rests on currently unproven hardness assumptions. ==Definition== Let $\backslash mathcal\; A\; =\; \backslash ^$ *\} be a class of functions. These functions are the ''statistical tests'' that the pseudorandom generator will try to fool, and they are usually algorithms. Sometimes the statistical tests are also called ''adversaries''. A function $G:\; \backslash ^\backslash ell\backslash to\backslash ^n$ with $\backslash ell\; \backslash leq\; n$ is a ''pseudorandom generator'' against $\backslash mathcal\; A$ with ''bias'' $\backslash epsilon$ if, for every $A$ in $\backslash mathcal\; A$, the statistical distance between the distributions $A(G(U\_\backslash ell))$ and $A(U\_n)$ is at most $\backslash epsilon$, where $U\_k$ is the uniform distribution on $\backslash ^k$. The quantity $\backslash ell$ is called the ''seed length'' and the quantity $n-\backslash ell$ is called the ''stretch'' of the pseudorandom generator. A pseudorandom generator against a family of adversaries $(\backslash mathcal\; A\_n)\_$ with bias $\backslash epsilon(n)$ is a family of pseudorandom generators $(G\_n)\_$, where $G\_n\; :\; \backslash ^\backslash to\backslash ^n$ is a pseudorandom generator against $\backslash mathcal\; A\_n$ with bias $\backslash epsilon(n)$ and seed length $\backslash ell(n)$. In most applications, the family $\backslash mathcal\; A$ represents some model of computation or some set of algorithms, and one is interested in designing a pseudorandom generator with small seed length and bias, and such that the output of the generator can be computed by the same sort of algorithm. 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 generator」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.