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OpenDarwin 7.2.1 - man page for random (opendarwin section 4)

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

     random , urandom -- random data source devices.

     pseudo-device random

     The random device produces uniformly distributed random byte values of potentially high

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

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

     /dev/urandom is a compatibility nod to Linux. On Linux, /dev/urandom will produce lower
     quality output if the entropy pool drains, while /dev/random 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.

     The random device implements the Yarrow pseudo random number generator algorithm and main-
     tains its entropy pool.  Addditional entropy is fed to the generator regularly by the
     SecurityServer daemon from random jitter measurements of the kernel.  SecurityServer is also
     responsible for periodically 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 random device, though
     this is not required in a normal operating environment.

     Yarrow 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 SecurityServer system daemon fails for any reason, output quality will suffer over time
     without any explicit indication from the random device itself.

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


     A random device appeared in Linux operating system.

Darwin					September 6, 2001				   Darwin

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