## Linux and UNIX Man Pages

Test Your Knowledge in Computers #267
Difficulty: Easy
In 1935, at the age of 22, Alan Turning was elected a fellow of King's on the strength of a dissertation in which he proved the central limit theorem.
True or False?

# arc4random_uniform(3) [freebsd man page]

```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 *buf, size_t nbytes);

uint32_t
arc4random_uniform(uint32_t upper_bound);

void
arc4random_stir(void);

void

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 (2**1700) states.  The arc4random() function returns pseudo-random numbers 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.

EXAMPLES
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)

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.

BSD								  April 15, 1997							       BSD```

## Check Out this Related Man Page

```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 *buf, size_t nbytes);

uint32_t
arc4random_uniform(uint32_t upper_bound);

void
arc4random_stir(void);

void

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 (2**1700) states.  The arc4random() function returns pseudo-random numbers 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.

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

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