| 1 | =================================
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| 2 | Hardware random number generators
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| 3 | =================================
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| 4 |
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| 5 | Introduction
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| 6 | ============
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| 7 |
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| 8 | The hw_random framework is software that makes use of a
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| 9 | special hardware feature on your CPU or motherboard,
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| 10 | a Random Number Generator (RNG). The software has two parts:
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| 11 | a core providing the /dev/hwrng character device and its
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| 12 | sysfs support, plus a hardware-specific driver that plugs
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| 13 | into that core.
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| 14 |
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| 15 | To make the most effective use of these mechanisms, you
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| 16 | should download the support software as well. Download the
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| 17 | latest version of the "rng-tools" package from:
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| 18 |
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| 19 | https://github.com/nhorman/rng-tools
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| 20 |
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| 21 | Those tools use /dev/hwrng to fill the kernel entropy pool,
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| 22 | which is used internally and exported by the /dev/urandom and
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| 23 | /dev/random special files.
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| 24 |
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| 25 | Theory of operation
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| 26 | ===================
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| 27 |
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| 28 | CHARACTER DEVICE. Using the standard open()
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| 29 | and read() system calls, you can read random data from
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| 30 | the hardware RNG device. This data is NOT CHECKED by any
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| 31 | fitness tests, and could potentially be bogus (if the
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| 32 | hardware is faulty or has been tampered with). Data is only
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| 33 | output if the hardware "has-data" flag is set, but nevertheless
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| 34 | a security-conscious person would run fitness tests on the
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| 35 | data before assuming it is truly random.
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| 36 |
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| 37 | The rng-tools package uses such tests in "rngd", and lets you
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| 38 | run them by hand with a "rngtest" utility.
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| 39 |
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| 40 | /dev/hwrng is char device major 10, minor 183.
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| 41 |
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| 42 | CLASS DEVICE. There is a /sys/class/misc/hw_random node with
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| 43 | two unique attributes, "rng_available" and "rng_current". The
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| 44 | "rng_available" attribute lists the hardware-specific drivers
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| 45 | available, while "rng_current" lists the one which is currently
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| 46 | connected to /dev/hwrng. If your system has more than one
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| 47 | RNG available, you may change the one used by writing a name from
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| 48 | the list in "rng_available" into "rng_current".
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| 49 |
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| 50 | ==========================================================================
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| 51 |
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| 52 |
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| 53 | Hardware driver for Intel/AMD/VIA Random Number Generators (RNG)
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| 54 | - Copyright 2000,2001 Jeff Garzik <[email protected]>
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| 55 | - Copyright 2000,2001 Philipp Rumpf <[email protected]>
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| 56 |
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| 57 |
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| 58 | About the Intel RNG hardware, from the firmware hub datasheet
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| 59 | =============================================================
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| 60 |
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| 61 | The Firmware Hub integrates a Random Number Generator (RNG)
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| 62 | using thermal noise generated from inherently random quantum
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| 63 | mechanical properties of silicon. When not generating new random
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| 64 | bits the RNG circuitry will enter a low power state. Intel will
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| 65 | provide a binary software driver to give third party software
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| 66 | access to our RNG for use as a security feature. At this time,
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| 67 | the RNG is only to be used with a system in an OS-present state.
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| 68 |
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| 69 | Intel RNG Driver notes
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| 70 | ======================
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| 71 |
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| 72 | FIXME: support poll(2)
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| 73 |
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| 74 | .. note::
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| 75 |
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| 76 | request_mem_region was removed, for three reasons:
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| 77 |
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| 78 | 1) Only one RNG is supported by this driver;
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| 79 | 2) The location used by the RNG is a fixed location in
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| 80 | MMIO-addressable memory;
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| 81 | 3) users with properly working BIOS e820 handling will always
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| 82 | have the region in which the RNG is located reserved, so
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| 83 | request_mem_region calls always fail for proper setups.
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| 84 | However, for people who use mem=XX, BIOS e820 information is
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| 85 | **not** in /proc/iomem, and request_mem_region(RNG_ADDR) can
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| 86 | succeed.
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| 87 |
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| 88 | Driver details
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| 89 | ==============
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| 90 |
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| 91 | Based on:
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| 92 | Intel 82802AB/82802AC Firmware Hub (FWH) Datasheet
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| 93 | May 1999 Order Number: 290658-002 R
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| 94 |
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| 95 | Intel 82802 Firmware Hub:
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| 96 | Random Number Generator
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| 97 | Programmer's Reference Manual
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| 98 | December 1999 Order Number: 298029-001 R
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| 99 |
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| 100 | Intel 82802 Firmware HUB Random Number Generator Driver
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| 101 | Copyright (c) 2000 Matt Sottek <[email protected]>
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| 102 |
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| 103 | Special thanks to Matt Sottek. I did the "guts", he
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| 104 | did the "brains" and all the testing.
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