1.\" $OpenBSD: random.4,v 1.10 2000/06/19 03:21:51 deraadt Exp $ 2.\" 3.\" Copyright (c) 1996, 1997 Michael Shalayeff 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 3. All advertising materials mentioning features or use of this software 14.\" must display the following acknowledgement: 15.\" This product includes software developed by Michael Shalayeff. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.Dd March 25, 1996 33.Dt RANDOM 4 34.Os 35.Sh NAME 36.Nm random , 37.Nm srandom , 38.Nm urandom , 39.Nm prandom , 40.Nm arandom 41.Nd random data source devices 42.Sh SYNOPSIS 43.Fd #include <sys/types.h> 44.Fd #include <dev/rndvar.h> 45.Fd #include <dev/rndioctl.h> 46.Sh DESCRIPTION 47The various 48.Nm 49devices produce random output data with different random qualities. 50Entropy data is collected from system activity (like disk and 51network device interrupts and such), and then run through various 52hash or message digest functions to generate the output. 53.Pp 54.Bl -hang -width /dev/srandomX 55.It /dev/random 56This device is reserved for future support of hardware 57random generators. 58.It /dev/srandom 59Strong random data. This device returns reliable random data. 60If sufficient entropy is not currently available (i.e., the entropy 61pool quality starts to run low), the driver pauses while more of 62such data is collected. 63The entropy pool data is converted into output data using MD5. 64.It /dev/urandom 65Same as above, but does not guarantee the data to be strong. 66The entropy pool data is converted into output data using MD5. 67When the entropy pool quality runs low, the driver will continue 68to output data. 69.It /dev/prandom 70Simple pseudo-random generator. 71.It /dev/arandom 72As required, entropy pool data re-seeds an ARC4 generator, 73which then generates high-quality pseudo-random output data. 74The 75.Xr arc4random 3 76function in userland libraries seeds itself from this device, 77providing a second level of ARC4 hashed data. 78.Sh SEE ALSO 79.Xr arc4random 3 , 80.Xr md5 3 , 81.Xr random 3 , 82.Xr pchb 4 , 83.Xr md5 9 , 84.Xr random 9 85.Sh FILES 86.Bl -tag -width /dev/srandom 87.It Pa /dev/random, /dev/srandom, /dev/urandom, /dev/prandom, /dev/arandom 88.El 89.Sh BUGS 90No randomness testing suite provided. 91.Sh HISTORY 92A 93.Nm 94device first appeared in Linux operating system. This is a cloned interface. 95.Pp 96ARC4 routines added by David Mazieres. 97