NAME    [Toc]    [Back]

     random, srandom, urandom, prandom,  arandom  -  random  data
source devices

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <dev/rndvar.h>
     #include <dev/rndioctl.h>

DESCRIPTION    [Toc]    [Back]

     The  various  random devices produce random output data with
different random
 qualities.  Entropy data is collected from system activity (like disk
     and  network  device  interrupts  and  such),  and  then run
through various
     hash or message digest functions to generate the output.

     /dev/random    This device is reserved for future support of
hardware
                    random generators.

     /dev/srandom    Strong random data.  This device returns reliable random
                    data.  If sufficient entropy is not currently
available
                    (i.e., the entropy pool quality starts to run
low), the
                    driver pauses while more of such data is collected.  The
                    entropy  pool  data  is converted into output
data using MD5.

     /dev/urandom   Same as above, but does not guarantee the data to be
                    strong.   The  entropy pool data is converted
into output
                    data using MD5.  When the entropy pool quality runs low,
                    the driver will continue to output data.

     /dev/prandom   Simple pseudo-random generator.

     /dev/arandom    As  required,  entropy pool data re-seeds an
ARC4 generator,
                    which then generates high-quality pseudo-random output data.


                    The  arc4random(3)  function  in userland libraries seeds itself
 from this  device,  providing  a  second
level of ARC4
                    hashed data.

FILES    [Toc]    [Back]

     /dev/random
     /dev/srandom
     /dev/urandom
     /dev/prandom
     /dev/arandom

SEE ALSO    [Toc]    [Back]

     arc4random(3), md5(3), random(3), amdpm(4), pchb(4), md5(9),
random(9)

HISTORY    [Toc]    [Back]

     A random device first appeared in  Linux  operating  system.
This is a
     cloned interface.

     ARC4 routines added by David Mazieres.

BUGS    [Toc]    [Back]

     No randomness testing suite provided.

OpenBSD      3.6                          March      25,     1996