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arc4random(3) [netbsd man page]

ARC4RANDOM(3)						   BSD Library Functions Manual 					     ARC4RANDOM(3)

NAME
arc4random, arc4random_buf, arc4random_uniform, arc4random_stir, arc4random_addrandom -- arc4 random number generator LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <stdlib.h> uint32_t arc4random(void); void arc4random_buf(void *buffer, size_t length); uint32_t arc4random_uniform(uint32_t upper_bound); void arc4random_stir(void); void arc4random_addrandom(u_char *dat, int datlen); DESCRIPTION
The arc4random() function provides a high quality 32-bit pseudo-random number very quickly. arc4random() seeds itself on a regular basis from the kernel strong random number subsystem described in rnd(4). On each call, an ARC4 generator is used to generate a new result. The arc4random() function uses the ARC4 cipher key stream generator, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2**1700) states. arc4random() fits into a middle ground not covered by other subsystems such as the strong, slow, and resource expensive random devices described in rnd(4) versus the fast but poor quality interfaces described in rand(3), random(3), and drand48(3). The arc4random_buf() function fills the buffer with length bytes of ARC4-derived random data. The arc4random_uniform() function returns a uniformly distributed random number less than upper_bound avoiding modulo bias when the upper bound is not a power of two. The arc4random_stir() function reads data from /dev/urandom and uses it to permute the S-Boxes via arc4random_addrandom(). There is no need to call arc4random_stir() before using arc4random(), since arc4random() automatically initializes itself. SEE ALSO
rand(3), rand48(3), random(3) HISTORY
An algorithm called RC4 was designed by RSA Data Security, Inc. It was considered a trade secret, but not trademarked. Because it was a trade secret, it obviously could not be patented. A clone of this was posted anonymously to USENET and confirmed to be equivalent by several sources who had access to the original cipher. Because of the trade secret situation, RSA Data Security, Inc. can do nothing about the release of the ARC4 algorithm. Since RC4 used to be a trade secret, the cipher is now referred to as ARC4. These functions first appeared in OpenBSD 2.1. BSD
February 4, 2011 BSD

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ARC4RANDOM(3)						   BSD Library Functions Manual 					     ARC4RANDOM(3)

NAME
arc4random, arc4random_buf, arc4random_uniform, arc4random_stir, arc4random_addrandom -- arc4 random number generator LIBRARY
Utility functions from BSD systems (libbsd, -lbsd) SYNOPSIS
#include <bsd/stdlib.h> u_int32_t arc4random(void); void arc4random_buf(void *buf, size_t nbytes); u_int32_t arc4random_uniform(u_int32_t upper_bound); void arc4random_stir(void); void arc4random_addrandom(unsigned char *dat, int datlen); DESCRIPTION
The arc4random() function uses the key stream generator employed by the arc4 cipher, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about (2**1700) states. The arc4random() function returns pseudo-random numbers in the range of 0 to (2**32)-1, and therefore has twice the range of rand(3) and random(3). arc4random_buf() function fills the region buf of length nbytes with ARC4-derived random data. arc4random_uniform() will return a uniformly distributed random number less than upper_bound. arc4random_uniform() is recommended over con- structions like ``arc4random() % upper_bound'' as it avoids "modulo bias" when the upper bound is not a power of two. The arc4random_stir() function reads data from /dev/urandom and uses it to permute the S-Boxes via arc4random_addrandom(). There is no need to call arc4random_stir() before using arc4random() functions family, since they automatically initialize themselves. EXAMPLES
The following produces a drop-in replacement for the traditional rand() and random() functions using arc4random(): #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1)) SEE ALSO
rand(3), random(3), srandomdev(3) HISTORY
RC4 has been designed by RSA Data Security, Inc. It was posted anonymously to the USENET and was confirmed to be equivalent by several sources who had access to the original cipher. Since RC4 used to be a trade secret, the cipher is now referred to as ARC4. BSD
April 15, 1997 BSD

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