Root/Documentation/hw_random.txt

1Introduction:
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/hw_random 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/hw_random to fill the kernel entropy pool,
18    which is used internally and exported by the /dev/urandom and
19    /dev/random special files.
20
21Theory 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/hw_random 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/hw_random. 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
52About 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
62Intel RNG Driver notes:
63
64    * FIXME: support poll(2)
65
66    NOTE: request_mem_region was removed, for two 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
76Driver 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.
91

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