path: root/Documentation/hw_random.txt
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authorLinus Torvalds <>2005-04-16 15:20:36 -0700
committerLinus Torvalds <>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/hw_random.txt
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+ Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
+ Copyright 2000,2001 Jeff Garzik <>
+ Copyright 2000,2001 Philipp Rumpf <>
+ The hw_random device driver is software that makes use of a
+ special hardware feature on your CPU or motherboard,
+ a Random Number Generator (RNG).
+ In order to make effective use of this device driver, 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:
+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.
+Theory of operation:
+ Character driver. 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.
+ /dev/hwrandom is char device major 10, minor 183.
+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.