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