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random(4) [mojave man page]

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

NAME
random , urandom -- random data source devices. SYNOPSIS
pseudo-device random DESCRIPTION
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. The same random data is also available from getentropy(2). Using the getentropy(2) system call interface will provide resiliency to file descriptor exhaustion, chroot, or sandboxing which can make /dev/random unavailable. Additionally, the arc4random(3) API provides a fast userspace random number generator built on the random data source and is preferred over directly accessing the system's random device. /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. The kernel automatically seeds the algorithm with additional entropy during normal execution. FILES
/dev/random /dev/urandom HISTORY
A random device appeared in the Linux operating system. Darwin September 6, 2001 Darwin

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

NAME
random , urandom -- random data source devices. SYNOPSIS
pseudo-device random DESCRIPTION
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. OPERATION
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 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 envi- ronment. 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 regu- lar 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 seed- ing it into random directly before obtaining important random numbers. FILES
/dev/random /dev/urandom HISTORY
A random device appeared in the Linux operating system. Darwin September 6, 2001 Darwin

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