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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
     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 situ-
     ation, 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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