[linux-2.6-block.git] / Documentation / hw_random.txt

Introduction:

	The hw_random framework is software that makes use of a
	special hardware feature on your CPU or motherboard,
	a Random Number Generator (RNG).  The software has two parts:
	a core providing the /dev/hw_random character device and its
	sysfs support, plus a hardware-specific driver that plugs
	into that core.

	To make the most effective use of these mechanisms, you
	should download the support software as well.  Download the
	latest version of the "rng-tools" package from the
	hw_random driver's official Web site:

		http://sourceforge.net/projects/gkernel/

	Those tools use /dev/hw_random to fill the kernel entropy pool,
	which is used internally and exported by the /dev/urandom and
	/dev/random special files.

Theory of operation:

	CHARACTER DEVICE.  Using the standard open()
	and read() system calls, you can read random data from
	the hardware RNG device.  This data is NOT CHECKED by any
	fitness tests, and could potentially be bogus (if the
	hardware is faulty or has been tampered with).  Data is only
	output if the hardware "has-data" flag is set, but nevertheless
	a security-conscious person would run fitness tests on the
	data before assuming it is truly random.

	The rng-tools package uses such tests in "rngd", and lets you
	run them by hand with a "rngtest" utility.

	/dev/hw_random is char device major 10, minor 183.

	CLASS DEVICE.  There is a /sys/class/misc/hw_random node with
	two unique attributes, "rng_available" and "rng_current".  The
	"rng_available" attribute lists the hardware-specific drivers
	available, while "rng_current" lists the one which is currently
	connected to /dev/hw_random.  If your system has more than one
	RNG available, you may change the one used by writing a name from
	the list in "rng_available" into "rng_current".

==========================================================================

	Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
	Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
	Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>


About the Intel RNG hardware, from the firmware hub datasheet:

	The Firmware Hub integrates a Random Number Generator (RNG)
	using thermal noise generated from inherently random quantum
	mechanical properties of silicon. When not generating new random
	bits the RNG circuitry will enter a low power state. Intel will
	provide a binary software driver to give third party software
	access to our RNG for use as a security feature. At this time,
	the RNG is only to be used with a system in an OS-present state.

Intel RNG Driver notes:

	* FIXME: support poll(2)

	NOTE: request_mem_region was removed, for three reasons:
	1) Only one RNG is supported by this driver, 2) The location
	used by the RNG is a fixed location in MMIO-addressable memory,
	3) users with properly working BIOS e820 handling will always
	have the region in which the RNG is located reserved, so
	request_mem_region calls always fail for proper setups.
	However, for people who use mem=XX, BIOS e820 information is
	-not- in /proc/iomem, and request_mem_region(RNG_ADDR) can
	succeed.

Driver details:

	Based on:
	Intel 82802AB/82802AC Firmware Hub (FWH) Datasheet
		May 1999 Order Number: 290658-002 R

	Intel 82802 Firmware Hub: Random Number Generator
	Programmer's Reference Manual
		December 1999 Order Number: 298029-001 R

	Intel 82802 Firmware HUB Random Number Generator Driver
	Copyright (c) 2000 Matt Sottek <msottek@quiknet.com>

	Special thanks to Matt Sottek.  I did the "guts", he
	did the "brains" and all the testing.
Commit	Line	Data
1da177e4 LT	1	Introduction:
1da177e4 LT	2
537878d2	3	The hw_random framework is software that makes use of a
1da177e4	4	special hardware feature on your CPU or motherboard,
537878d2 DB	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.
1da177e4	9
537878d2	10	To make the most effective use of these mechanisms, you
1da177e4 LT	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
537878d2 DB	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.
1da177e4 LT	20
	21	Theory of operation:
	22
537878d2	23	CHARACTER DEVICE. Using the standard open()
1da177e4 LT	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
537878d2 DB	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
	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.
1da177e4	61
537878d2	62	Intel RNG Driver notes:
1da177e4 LT	63
	64	* FIXME: support poll(2)
	65
6375bcf7	66	NOTE: request_mem_region was removed, for three reasons:
1da177e4 LT	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.