- stretch 0.8.3-1
|ARC4RANDOM(3)||Library Functions Manual||ARC4RANDOM(3)|
char *dat, int
DESCRIPTION¶This family of functions provides higher quality data than those described in rand(3), random(3), and rand48(3).
Use of these functions is encouraged for almost all random number consumption because the other interfaces are deficient in either quality, portability, standardization, or availability. These functions can be called in almost all coding environments, including pthreads(3) and chroot(2).
High quality 32-bit pseudo-random numbers are generated very quickly. On each call, a cryptographic pseudo-random number generator is used to generate a new result. One data pool is used for all consumers in a process, so that consumption under program flow can act as additional stirring. The subsystem is re-seeded from the kernel random number subsystem using getentropy(2) on a regular basis, and also upon fork(2).
arc4random() function returns a single
arc4random_buf() function fills the
region buf of length nbytes with
arc4random_uniform() will return a single
32-bit value, uniformly distributed but less than
upper_bound. This is recommended over constructions
arc4random() % upper_bound” as
it avoids "modulo bias" when the upper bound is not a power of
two. In the worst case, this function may consume multiple iterations to
ensure uniformity; see the source code to understand the problem and
arc4random_stir() function reads data
from getentropy(2) and uses it to re-seed the subsystem
There is no need to call
arc4random() functions family, since
they automatically initialize themselves.
RETURN VALUES¶These functions are always successful, and no return value is reserved to indicate an error.
SEE ALSO¶rand(3), rand48(3), random(3)
HISTORY¶These functions first appeared in OpenBSD 2.1.
The original version of this random number generator used the RC4 (also known as ARC4) algorithm. In OpenBSD 5.5 it was replaced with the ChaCha20 cipher, and it may be replaced again in the future as cryptographic techniques advance. A good mnemonic is “A Replacement Call for Random”.
|July 19, 2014||Linux 4.9.0-9-amd64|