arc4rand(9) [debian man page]

RANDOM(9)						   BSD Kernel Developer's Manual						 RANDOM(9)

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 num-
     bers 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, approxi-
     mately 16*((2**31)-1).

     The arc4rand() function uses the RC4 algorithm to generate successive pseudo-random bytes.  The arc4random() function uses arc4rand() to gen-
     erate 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().

BSD
								September 25, 2000							       BSD

Check Out this Related Man Page

RANDOM(3)						     Linux Programmer's Manual							 RANDOM(3)

NAME

       random, srandom, initstate, setstate - random number generator.

SYNOPSIS

       #include <stdlib.h>

       long int random(void);
       void srandom(unsigned int seed);
       char *initstate(unsigned int seed, char *state, size_t n);
       char *setstate(char *state);

DESCRIPTION

       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 RAND_MAX.  The period of this random number generator is very large, approx-
       imately 16*((2**31)-1).

       The  srandom()  function  sets  its  argument  as  the seed for a new sequence of pseudo-random integers to be returned by random().  These
       sequences are repeatable by calling srandom() with the same seed value.	If no seed value is provided, the random() function  is  automati-
       cally seeded with a value of 1.

       The  initstate() function allows a state array state to be initialized for use by random().  The size of the state array n is used by init-
       state() to decide how sophisticated a random number generator it should use -- the larger the state array, the better  the  random  numbers
       will  be.   seed  is  the  seed	for  the initialization, which specifies a starting point for the random number sequence, and provides for
       restarting at the same point.

       The setstate() function changes the state array used by the random() function.  The state array state is used for random number	generation
       until  the next call to initstate() or setstate().  state must first have been initialized using initstate() or be the result of a previous
       call of setstate().

RETURN VALUE

       The random() function returns a value between 0 and RAND_MAX.  The srandom() function returns no value.	 The  initstate()  and	setstate()
       functions return a pointer to the previous state array, or NULL on error.

ERRORS

       EINVAL A state array of less than 8 bytes was specified to initstate().

NOTES

       Current	"optimal"  values  for	the size of the state array n are 8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to the
       nearest known amount.  Using less than 8 bytes will cause an error.

CONFORMING TO

       BSD 4.3

SEE ALSO

       rand(3), srand(3)

GNU
								    2000-08-20								 RANDOM(3)

Linux and UNIX Man Pages

arc4rand(9) [debian man page]

Check Out this Related Man Page