NAME

       arc4rand, arc4random, random, read_random, srandom — supply pseudo-random numbers

SYNOPSIS

       #include <sys/libkern.h>

       void
       srandom(u_long seed);

       u_long
       random(void);

       void
       arc4rand(void *ptr, u_int length, int reseed);

       u_int32_t
       arc4random(void);

       #include <sys/random.h>

       int
       read_random(void *buffer, int count);

DESCRIPTION

       The  random()  function  will  by default produce a sequence of numbers that can be duplicated by calling
       srandom() with ‘1’ as the seed.  The srandom() function may be called with any arbitrary  seed  value  to
       get  slightly  more  unpredictable  numbers.   It  is important to remember that the random() function is
       entirely predictable, and is therefore not of use where knowledge of the sequence of numbers  may  be  of
       benefit to an attacker.

       The  arc4rand()  function  will  return  very  good  quality  random  numbers, slightly better suited for
       security-related purposes.  The random numbers from arc4rand() are seeded from the entropy device  if  it
       is  available.  Automatic reseeds happen after a certain timeinterval and after a certain number of bytes
       have been delivered.  A forced reseed can be forced by passing a non-zero value in the reseed argument.

       The read_random() function is used to return entropy directly from the entropy  device  if  it  has  been
       loaded.   If  the  entropy  device  is  not  loaded,  then  the buffer is filled with output generated by
       random().  The buffer is filled with no more than count bytes.  It is advised that read_random()  is  not
       used; instead use arc4rand()

       All  the bits generated by random(), arc4rand() and read_random() are usable.  For example, ‘random()&01’
       will produce a random binary value.

       The arc4random() is a convenience function which calls  arc4rand()  to  return  a  32  bit  pseudo-random
       integer.

RETURN VALUES

       The  random()  function  uses  a non-linear additive feedback random number generator employing a default
       table of size 31 long integers to return  successive  pseudo-random  numbers  in  the  range  from  0  to
       (2**31)−1.  The period of this random number generator is very large, approximately 16*((2**31)−1).

       The  arc4rand()  function  uses  the  RC4  algorithm  to  generate  successive  pseudo-random bytes.  The
       arc4random() function uses arc4rand() to generate pseudo-random numbers in the range from 0 to (2**32)−1.

       The read_random() function returns the number of bytes placed in buffer.

AUTHORS

       Dan Moschuk wrote arc4random().
       Mark R V Murray wrote read_random().

Debian                                         September 25, 2000                                      RANDOM(9)