106 lines
3.7 KiB
ReStructuredText
106 lines
3.7 KiB
ReStructuredText
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Hardware random number generators
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=================================
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Introduction
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============
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The hw_random framework is software that makes use of a
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special hardware feature on your CPU or motherboard,
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a Random Number Generator (RNG). The software has two parts:
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a core providing the /dev/hwrng character device and its
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sysfs support, plus a hardware-specific driver that plugs
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into that core.
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To make the most effective use of these mechanisms, you
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should download the support software as well. Download the
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latest version of the "rng-tools" package from the
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hw_random driver's official Web site:
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http://sourceforge.net/projects/gkernel/
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Those tools use /dev/hwrng to fill the kernel entropy pool,
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which is used internally and exported by the /dev/urandom and
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/dev/random special files.
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Theory of operation
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===================
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CHARACTER DEVICE. Using the standard open()
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and read() system calls, you can read random data from
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the hardware RNG device. This data is NOT CHECKED by any
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fitness tests, and could potentially be bogus (if the
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hardware is faulty or has been tampered with). Data is only
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output if the hardware "has-data" flag is set, but nevertheless
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a security-conscious person would run fitness tests on the
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data before assuming it is truly random.
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The rng-tools package uses such tests in "rngd", and lets you
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run them by hand with a "rngtest" utility.
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/dev/hwrng is char device major 10, minor 183.
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CLASS DEVICE. There is a /sys/class/misc/hw_random node with
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two unique attributes, "rng_available" and "rng_current". The
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"rng_available" attribute lists the hardware-specific drivers
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available, while "rng_current" lists the one which is currently
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connected to /dev/hwrng. If your system has more than one
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RNG available, you may change the one used by writing a name from
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the list in "rng_available" into "rng_current".
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==========================================================================
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Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
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- Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
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- Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
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About the Intel RNG hardware, from the firmware hub datasheet
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=============================================================
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The Firmware Hub integrates a Random Number Generator (RNG)
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using thermal noise generated from inherently random quantum
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mechanical properties of silicon. When not generating new random
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bits the RNG circuitry will enter a low power state. Intel will
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provide a binary software driver to give third party software
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access to our RNG for use as a security feature. At this time,
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the RNG is only to be used with a system in an OS-present state.
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Intel RNG Driver notes
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======================
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FIXME: support poll(2)
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.. note::
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request_mem_region was removed, for three reasons:
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1) Only one RNG is supported by this driver;
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2) The location used by the RNG is a fixed location in
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MMIO-addressable memory;
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3) users with properly working BIOS e820 handling will always
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have the region in which the RNG is located reserved, so
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request_mem_region calls always fail for proper setups.
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However, for people who use mem=XX, BIOS e820 information is
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**not** in /proc/iomem, and request_mem_region(RNG_ADDR) can
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succeed.
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Driver details
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==============
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Based on:
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Intel 82802AB/82802AC Firmware Hub (FWH) Datasheet
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May 1999 Order Number: 290658-002 R
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Intel 82802 Firmware Hub:
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Random Number Generator
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Programmer's Reference Manual
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December 1999 Order Number: 298029-001 R
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Intel 82802 Firmware HUB Random Number Generator Driver
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Copyright (c) 2000 Matt Sottek <msottek@quiknet.com>
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Special thanks to Matt Sottek. I did the "guts", he
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did the "brains" and all the testing.
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