[Cryptography] Mac OS 10.7.5 Random Numbers
frantz at pwpconsult.com
Sat Feb 1 01:06:27 EST 2014
The man page for random/urandom on MacOS is an interesting contribution to the random
XXXXX:~ yyyyy$ man random
RANDOM(4) BSD Kernel Interfaces Manual RANDOM(4)
random , urandom -- random data source devices.
The random device produces uniformly distributed random byte values of
potentially high quality.
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 maintains its entropy pool. Additional 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
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.
LIMITATIONS AND WARNINGS
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 counteract 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 the Linux operating system.
Darwin September 6, 2001 Darwin
Cheers - Bill
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