arc4random_buf man page on OpenBSD

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ARC4RANDOM(3)		  OpenBSD Programmer's Manual		 ARC4RANDOM(3)

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

     #include <stdlib.h>


     arc4random_buf(void *buf, size_t nbytes);

     arc4random_uniform(u_int32_t upper_bound);


     arc4random_addrandom(u_char *dat, int datlen);

     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 random(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 random(4) versus the fast but poor quality interfaces described in
     rand(3), random(3), and drand48(3).

     arc4random_buf() 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 using sysctl(3) from
     kern.arandom and uses it to permute the S-Boxes via

     There is no need to call arc4random_stir() before using arc4random(),
     since arc4random() automatically initializes itself.

     These functions are always successful, and no return value is reserved to
     indicate an error.

     rand(3), rand48(3), random(3)

     An algorithm called RC4 was designed by RSA Data Security, Inc.  It was
     considered a trade secret.	 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. could do nothing about the release of the `Alleged RC4'
     algorithm.	 Since RC4 was trademarked, the cipher is now referred to as

     These functions first appeared in OpenBSD 2.1.

OpenBSD 4.9		       December 23, 2008		   OpenBSD 4.9

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