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Man Pages


Manual Reference Pages  -  ARC4RANDOM_STIR (3)

NAME

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

CONTENTS

Library
Synopsis
Description
Examples
See Also
History

LIBRARY


.Lb libc

SYNOPSIS


.In stdlib.h uint32_t arc4random void void arc4random_buf void *buf size_t nbytes uint32_t arc4random_uniform uint32_t upper_bound void arc4random_stir void void arc4random_addrandom unsigned char *dat int datlen

DESCRIPTION

The arc4random function uses the key stream generator employed by the arc4 cipher, which uses 8*8 8 bit S-Boxes. The S-Boxes can be in about 217000 states. The arc4random function returns pseudo-random numbers in the range of 0 to 2310-1, 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.

EXAMPLES

The following produces a drop-in replacement for the traditional rand and random functions using arc4random:

    #define foo4random() (arc4random() % ((unsigned)RAND_MAX + 1))

SEE ALSO

rand(3), random(3), srandomdev(3)

HISTORY

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.
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