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- 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:
- 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 <>
- Copyright 2000,2001 Philipp Rumpf <>
-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 two 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 <>
- Special thanks to Matt Sottek. I did the "guts", he
- did the "brains" and all the testing.