rng man page on HP-UX

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random(7)							     random(7)

NAME
       random, urandom, rng - strong random number generator

SYNOPSIS
DESCRIPTION
       The character special files and provide an interface to the kernel-res‐
       ident random number generator, A from is potentially blocking.  A  from
       is  always  nonblocking.	  Data from can potentially have lower entropy
       than data from

       The module is a dynamically loadable kernel module (DLKM).  That is, it
       can  be	dynamically  unconfigured  or reconfigured by an administrator
       with root authority without rebooting the system.

       A sequence from has unlimited entropy.  In contrast, a sequence	gener‐
       ated  computationally  by a pseudorandom number generator, such as ran‐
       dom(3M), has limited entropy, derived only from its initial seed.   The
       module  should  be  considered a quality source for randomness.	It has
       passed extensive statistical  testing,  including  the  NIST  (National
       Institute of Standards and Technology) tests for randomness.

       The  module  uses  the  uncertainty  in	completion  times of interrupt
       threads triggered by external events.  The module extracts  a  sequence
       of  bits	 from  the  interrupt  time  stamps.  Any existing bit bias is
       removed to yield a sequence with uniform distribution of 0's  and  1's.
       The  resulting  sequence is divided between the holding buffers for the
       special files and For each on and data is  retrieved  from  the	corre‐
       sponding	 holding  buffer.   A  hash  function  based  on AES (Advanced
       Encryption Standard) is applied and the result is placed in the	buffer
       provided	 by the user.  All requests on the holding buffers are serial‐
       ized to ensure that returned random data is not shared between  differ‐
       ent requests even for simultaneous requests on a multiprocessor system.

       There  is  no  function	associated with either or and both devices are
       read-only by all users.	A single is defined for to facilitate indepen‐
       dent verification of production.

       The file contains the following definitions:

	      /* The maximum request size, for read() or ioctl(), in bytes   */
	      #define RNG_READMAX    256

	      /* ioctl() to retrieve data from the entropy collector directly*/
	      #define RNG_GETRAW     _IOR('Q', 0, uint8_t[RNG_READMAX])

       If a request is for more than RNG_READMAX bytes, it is treated as if it
       was for exactly bytes.  This holds for both and

   Specific Information About /dev/random
       When there are a large number of requests on within a short time inter‐
       val, the demand on the holding buffer can exceed the rate at which data
       is supplied by A on the device blocks the requesting thread if the ran‐
       dom  data  stored  in  the  holding  buffer  is too low to complete the
       request.	 The thread blocks until the holding buffer has	 been  updated
       with enough random data to complete the request.

       For  flags, only and have device-specific actions.  If neither of these
       flags is set, a on will block until the amount of data requested, up to
       bytes,  can  be	returned.   When  the requested number of bytes is not
       available and either of the above flags are set,	 returns  immediately.
       If the flag is set, returns -1 and errno is set to If is not set and is
       set, returns zero.

       The permits an application with superuser privilege to fetch  bytes  of
       data  directly from the holding buffer, after bias has been removed but
       before the AES hash.  This interface is not intended  to	 be  used  for
       cryptographic applications, rather, for statistical testing of the ran‐
       domness of the data in the holding buffer.  This blocks	for  the  same
       reason  as  a  read on If the requesting thread does not have superuser
       authority, is returned.

   Specific Information About /dev/urandom
       To address the limited random data collection rate problem, the	device
       is  strictly nonblocking.  The holding buffer is regularly updated with
       random data, yet a high number of reads can decrease the entropy in its
       holding	buffer.	  Under	 this conditions, the entropy of the data from
       will be slightly lower that the one from yet can still be considered  a
       good source of random numbers.

       There are no flags that result in device-specific actions with

ERRORS
       For	      was  set when was opened, and there is insufficient con‐
		      tent in the holding buffer to complete the request.

       For the	      the requesting thread did not have superuser authority.

AUTHOR
       The random number generator was developed by HP.

       For bias removal, the generator uses an algorithm by Dr.	 Yuval	Perez,
       University of California.

       The  secure  hashing  uses  an AES implementation provided by Dr. Brian
       Gladman, UK.

       The NIST statistical tests are available at

FILES
SEE ALSO
       random(3M).

								     random(7)
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