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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 num- bers 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.


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 anony- mously 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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