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 (variance in fan noise or HDD), either pre-existing ones such as mouse movements or specially provided randomness generators. A lack of entropy can have a negative impact on performance and security. The Linux kernel generates entropy from keyboard timings, mouse movements, and integrated drive electronics (IDE) timings and makes the random character data available to other operating system processes through the s /dev/random and /dev/urandom. This capability was introduced in Linux version 1.3.30. There are some Linux kernel patches allowing one to use more entropy sources. The audio_entropyd project, which is included in some operating systems such as Fedora, allows audio data to be used as an entropy source. 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. In some systems, network interrupts can be used as an entropy source as well. OpenBSD security features OpenBSD has integrated cryptography as one of its main goals and has always worked on increasing its entropy for encryption but also for randomising many parts of the OS, including various internal operations of its kernel. Around 2011, two of the random devices were dropped and linked into a single source as it could produce hundreds of megabytes per second of high quality random data on an average system. This made depletion of random data by userland programs impossible on OpenBSD once enough entropy has initially been gathered. A driver ported from the Linux kernel has been made available for the Hurd kernel. /dev/random and /dev/urandom have been available as Sun packages or patches for Solaris since Solaris 2.