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Entropy (computing)
In computing, entropy is the randomness collected by an operating system or application for use in cryptography or other uses that require random data. This randomness is often collected from hardware sources, either pre-existing ones such as mouse movements or specially provided randomness generators.
== Linux kernel ==
The Linux kernel generates entropy from keyboard timings, mouse movements, and IDE timings and makes the random character data available to other operating system processes through the special files /dev/random and /dev/urandom. This capability was introduced in Linux version 1.3.30.〔(random(4) - Linux man page ) (die.net)〕
There are some Linux kernel patches allowing one to use more entropy sources.〔(Robotic Tendencies » Missing entropy )〕 The (audio_entropyd ) project, which is included in some operating systems such as Fedora, allows audio data to be used as an entropy source.〔(Fedora Package Database - audio-entropyd )〕 Also available are (video_entropyd ) which calculates random data from a video-source and (entropybroker ) which includes these three and can be used to distribute the entropy data to systems not capable of running any of these (e.g. virtual machines). Furthermore one can use the HAVEGE algorithm through haveged to pool entropy.〔(【引用サイトリンク】url=http://www.issihosts.com/haveged/ )〕 In some systems, network interrupts can be used as an entropy source as well.〔(Entropy and Random Devices | LinuxLink by TimeSys - Your Embedded Linux Resource )〕
On systems using the Linux kernel, programs needing significant amounts of random data from /dev/urandom cannot co-exist with programs reading little data from /dev/random, as /dev/urandom depletes /dev/random whenever it is being read.〔(High-Entropy Randomness Generator )〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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