arc4random(3) - NetBSD Manual Pages

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ARC4RANDOM(3)           NetBSD 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.

NetBSD 6.0.2                   February 4, 2011                   NetBSD 6.0.2