NAME

       arc4random, arc4random_uniform, arc4random_buf - cryptographically-secure pseudorandom number generator

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       uint32_t arc4random(void);
       uint32_t arc4random_uniform(uint32_t upper_bound);
       void arc4random_buf(void buf[.n], size_t n);

DESCRIPTION

       These functions give cryptographically-secure pseudorandom numbers.

       arc4random() returns a uniformly-distributed value.

       arc4random_uniform() returns a uniformly-distributed value less than upper_bound (see BUGS).

       arc4random_buf() fills the memory pointed to by buf, with n bytes of pseudorandom data.

       The  rand(3)  and  drand48(3)  families  of  functions  should  only  be  used  where  the quality of the
       pseudorandom numbers is not a concern and there's a need for repeatability of the  results.   Unless  you
       meet both of those conditions, use the arc4random() functions.

RETURN VALUE

       arc4random() returns a pseudorandom number.

       arc4random_uniform()  returns  a  pseudorandom  number  less  than upper_bound for valid input, or 0 when
       upper_bound is invalid.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                                     │ Attribute     │ Value   │
       ├──────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │arc4random(), arc4random_uniform(), arc4random_buf()                          │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       BSD.

HISTORY

       OpenBSD 2.1, FreeBSD 3.0, NetBSD 1.6, DragonFly 1.0, libbsd, glibc 2.36.

BUGS

       An upper_bound of 0 doesn't make sense in a call to arc4random_uniform().  Such a  call  will  fail,  and
       return  0.   Be careful, since that value is not less than upper_bound.  In some cases, such as accessing
       an array, using that value could result in Undefined Behavior.

SEE ALSO

       getrandom(3), rand(3), drand48(3), random(7)