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ARC4RANDOM(3)         DragonFly Library Functions Manual         ARC4RANDOM(3)


arc4random, arc4random_buf, arc4random_uniform, arc4random_stir, arc4random_addrandom -- arc4 random number generator


Standard C Library (libc, -lc)


#include <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(uint8_t *dat, size_t datlen);


The arc4random() function uses the key stream generator employed by the arc4 cipher, which uses 256 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 constructions 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.


The following produces a drop-in replacement for the traditional rand() and random() functions using arc4random(): #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))


rand(3), random(3), srandomdev(3), urandom(4)


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. DragonFly 4.7 April 15, 1997 DragonFly 4.7

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