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Linux/Documentation/hw_random.txt

  1 Introduction:
  2 
  3         The hw_random framework is software that makes use of a
  4         special hardware feature on your CPU or motherboard,
  5         a Random Number Generator (RNG).  The software has two parts:
  6         a core providing the /dev/hwrng character device and its
  7         sysfs support, plus a hardware-specific driver that plugs
  8         into that core.
  9 
 10         To make the most effective use of these mechanisms, you
 11         should download the support software as well.  Download the
 12         latest version of the "rng-tools" package from the
 13         hw_random driver's official Web site:
 14 
 15                 http://sourceforge.net/projects/gkernel/
 16 
 17         Those tools use /dev/hwrng to fill the kernel entropy pool,
 18         which is used internally and exported by the /dev/urandom and
 19         /dev/random special files.
 20 
 21 Theory of operation:
 22 
 23         CHARACTER DEVICE.  Using the standard open()
 24         and read() system calls, you can read random data from
 25         the hardware RNG device.  This data is NOT CHECKED by any
 26         fitness tests, and could potentially be bogus (if the
 27         hardware is faulty or has been tampered with).  Data is only
 28         output if the hardware "has-data" flag is set, but nevertheless
 29         a security-conscious person would run fitness tests on the
 30         data before assuming it is truly random.
 31 
 32         The rng-tools package uses such tests in "rngd", and lets you
 33         run them by hand with a "rngtest" utility.
 34 
 35         /dev/hwrng is char device major 10, minor 183.
 36 
 37         CLASS DEVICE.  There is a /sys/class/misc/hw_random node with
 38         two unique attributes, "rng_available" and "rng_current".  The
 39         "rng_available" attribute lists the hardware-specific drivers
 40         available, while "rng_current" lists the one which is currently
 41         connected to /dev/hwrng.  If your system has more than one
 42         RNG available, you may change the one used by writing a name from
 43         the list in "rng_available" into "rng_current".
 44 
 45 ==========================================================================
 46 
 47         Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
 48         Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
 49         Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
 50 
 51 
 52 About the Intel RNG hardware, from the firmware hub datasheet:
 53 
 54         The Firmware Hub integrates a Random Number Generator (RNG)
 55         using thermal noise generated from inherently random quantum
 56         mechanical properties of silicon. When not generating new random
 57         bits the RNG circuitry will enter a low power state. Intel will
 58         provide a binary software driver to give third party software
 59         access to our RNG for use as a security feature. At this time,
 60         the RNG is only to be used with a system in an OS-present state.
 61 
 62 Intel RNG Driver notes:
 63 
 64         * FIXME: support poll(2)
 65 
 66         NOTE: request_mem_region was removed, for three reasons:
 67         1) Only one RNG is supported by this driver, 2) The location
 68         used by the RNG is a fixed location in MMIO-addressable memory,
 69         3) users with properly working BIOS e820 handling will always
 70         have the region in which the RNG is located reserved, so
 71         request_mem_region calls always fail for proper setups.
 72         However, for people who use mem=XX, BIOS e820 information is
 73         -not- in /proc/iomem, and request_mem_region(RNG_ADDR) can
 74         succeed.
 75 
 76 Driver details:
 77 
 78         Based on:
 79         Intel 82802AB/82802AC Firmware Hub (FWH) Datasheet
 80                 May 1999 Order Number: 290658-002 R
 81 
 82         Intel 82802 Firmware Hub: Random Number Generator
 83         Programmer's Reference Manual
 84                 December 1999 Order Number: 298029-001 R
 85 
 86         Intel 82802 Firmware HUB Random Number Generator Driver
 87         Copyright (c) 2000 Matt Sottek <msottek@quiknet.com>
 88 
 89         Special thanks to Matt Sottek.  I did the "guts", he
 90         did the "brains" and all the testing.

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