1.\" $NetBSD: rnd.9,v 1.12 2002/08/19 17:41:46 wiz Exp $ 2.\" 3.\" Copyright (c) 1997 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This documentation is derived from text contributed to The NetBSD 7.\" Foundation by S.P.Zeidler (aka stargazer). 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd October 20, 1997 38.Dt RND 9 39.Os 40.Sh NAME 41.Nm RND , 42.Nm rnd_attach_source , 43.Nm rnd_detach_source , 44.Nm rnd_add_data , 45.Nm rnd_add_uint32 46.Nd functions to make a device available for entropy collection 47.Sh SYNOPSIS 48.Fd #include \*[Lt]sys/rnd.h\*[Gt] 49.Ft void 50.Fn rnd_attach_source "rndsource_element_t *rnd_source" "char *devname" "u_int32_t source_type" "u_int32_t flags" 51.Ft void 52.Fn rnd_detach_source "rndsource_element_t *rnd_source" 53.Ft void 54.Fn rnd_add_data "rndsource_element_t *rnd_source" "void *data" "u_int32_t len" "u_int32_t entropy" 55.Ft void 56.Fn rnd_add_uint32 "rndsource_element_t *rnd_source" "u_int32_t datum" 57.Sh DESCRIPTION 58These 59.Nm 60functions make a device available for entropy collection for 61.Pa /dev/random . 62.Pp 63Ideally the first argument 64.Fa rnd_source 65of these functions gets included in the devices' entity struct, 66but any means to permanently (static) attach one such argument 67to one incarnation of the device is ok. Do not share 68.Fa rnd_source 69structures between two devices. 70.Pp 71.Bl -tag -width 8n 72.It Fn rnd_attach_source "rndsource_element_t *rnd_source" "char *devname" "u_int32_t source_type" "u_int32_t flags" 73This function announces the availability of a device for entropy collection. 74It must be called before the source struct pointed to by 75.Fa rnd_source 76is used in any of the following functions. 77.Pp 78.Fa devname 79is the name of the device. It is used to print a message (if the kernel is 80compiled with ``options RND_VERBOSE'') and also for status information printed 81with 82.Xr rndctl 8 . 83.Pp 84.Fa source_type 85is 86.Dv RND_TYPE_NET 87for network devices, 88.Dv RND_TYPE_DISK 89for physical disks, 90.Dv RND_TYPE_TAPE 91for a tape drive, and 92.Dv RND_TYPE_TTY 93for a tty. 94.Dv RND_TYPE_UNKNOWN 95is not to be used as a type. It is used internally to the rnd system. 96.Pp 97.Fa flags 98are the logical OR of 99.Dv RND_FLAG_NO_COLLECT 100(don't collect or estimate) 101.Dv RND_FLAG_NO_ESTIMATE 102(don't estimate) 103to control the default setting for collection and estimation. Note that 104devices of type 105.Dv RND_TYPE_NET 106default to 107.Dv RND_FLAG_NO_ESTIMATE . 108.Pp 109.It Fn rnd_detach_source "rndsource_element_t *rnd_source" 110This function disconnects the device from entropy collection. 111.It Fn rnd_add_uint32 "rndsource_element_t *rnd_source" "u_int32_t datum" 112This function adds the value of 113.Va datum 114to the entropy pool. No entropy is assumed to be collected from this value, 115it merely helps stir the entropy pool. All entropy is gathered from 116jitter between the timing of events. 117.Pp 118Note that using a constant for 119.Va datum 120does not weaken security, but it does 121not help. Try to use something that can change, such as an interrupt status 122register which might have a bit set for receive ready or transmit ready, 123or other device status information. 124.Pp 125To allow the system to gather the timing information accurately, this call 126should be placed within the actual hardware interrupt service routine. Care 127must be taken to ensure that the interrupt was actually serviced by the 128interrupt handler, since on some systems interrupts can be shared. 129.Pp 130This function loses nearly all usefulness if it is called from a scheduled 131software interrupt. If that is the only way to add the device as an entropy 132source, don't. 133.Pp 134If it is desired to mix in the 135.Va datum 136and to add in a timestamp, but not to actually estimate entropy from a source 137of randomness, passing 138.Dv NULL 139for 140.Va rnd_source 141is permitted, and the device does not need to be attached. 142.It Fn rnd_add_data "rndsource_element_t *rnd_source" "void *data" "u_int32_t len" "u_int32_t entropy" 143adds (hopefully) random 144.Fa data 145to the entropy pool. 146.Fa len 147is the number of bytes in 148.Fa data 149and 150.Fa entropy 151is an "entropy quality" measurement. 152If every bit of 153.Fa data 154is known to be random, 155.Fa entropy 156is the number of bits in 157.Fa data . 158.Pp 159Timing information is also used to add entropy into the system, using 160inter-event timings. 161.Pp 162If it is desired to mix in the 163.Va data 164and to add in a timestamp, but not to actually estimate entropy from a source 165of randomness, passing 166.Dv NULL 167for 168.Va rnd_source 169is permitted, and the device does not need to be attached. 170.El 171.\" .Sh ERRORS 172.Sh FILES 173These functions are declared in src/sys/sys/rnd.h and defined in 174src/sys/dev/rnd.c. 175.Sh SEE ALSO 176.Xr rnd 4 , 177.Xr rndctl 8 178.Sh HISTORY 179The random device was introduced in 180.Nx 1.3 . 181.Sh AUTHORS 182This implementation was written by Michael Graff \*[Lt]explorer@flame.org\*[Gt] 183using ideas and algorithms gathered from many sources, including 184the driver written by Ted Ts'o. 185.Sh BUGS 186The only good sources of randomness are quantum mechanical, and most 187computers avidly avoid having true sources of randomness included. 188Don't expect to surpass "pretty good". 189