RANDOM(4) BSD Kernel Interfaces Manual RANDOM(4)

NAME
     rraannddoomm , uurraannddoomm - random data source devices.

SYNOPSIS
     ppsseeuuddoo-ddeevviiccee rraannddoomm

DESCRIPTION
     The rraannddoomm device produces uniformly distributed random byte values of
     potentially high quality.

     To obtain random bytes, open //ddeevv//rraannddoomm for reading and read from it.

     To add entropy to the random generation system, open //ddeevv//rraannddoomm for
     writing and write data that you believe to be somehow random.

     //ddeevv//uurraannddoomm is a compatibility nod to Linux. On Linux, //ddeevv//uurraannddoomm will
     produce lower quality output if the entropy pool drains, while
     //ddeevv//rraannddoomm will prefer to block and wait for additional entropy to be
     collected.  With Yarrow, this choice and distinction is not necessary,
     and the two devices behave identically. You may use either.

OOPPEERRAATTIIOONN
     The rraannddoomm device implements the YYaarrrrooww pseudo random number generator
     algorithm and maintains its entropy pool.  Addditional entropy is fed to
     the generator regularly by the SSeeccuurriittyySSeerrvveerr daemon from random jitter
     measurements of the kernel.  SSeeccuurriittyySSeerrvveerr is also responsible for peri-
     odically saving some entropy to disk and reloading it during startup to
     provide entropy in early system operation.

     You may feed additional entropy to the generator by writing it to the
     rraannddoomm device, though this is not required in a normal operating environ-
     ment.

LLIIMMIITTAATTIIOONNSS AANNDD WWAARRNNIINNGGSS
     YYaarrrrooww is a fairly resilient algorithm, and is believed to be resistant
     to non-root.  The quality of its output is however dependent on regular
     addition of appropriate entropy. If the SSeeccuurriittyySSeerrvveerr system daemon
     fails for any reason, output quality will suffer over time without any
     explicit indication from the rraannddoomm device itself.

     Paranoid programmers can counter-act this risk somewhat by collecting
     entropy of their choice (e.g. from keystroke or mouse timings) and seed-
     ing it into rraannddoomm directly before obtaining important random numbers.

FILES     /dev/random
     /dev/urandom

HISTORY     A rraannddoomm device appeared in Linux operating system.

Darwin                         September 6, 2001                        Darwin