180 lines
5.3 KiB
Groff
180 lines
5.3 KiB
Groff
.\" Copyright (c) 2001 Mark R V Murray. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 10, 2001
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.Dt RANDOM 4
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.Os
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.Sh NAME
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.Nm random
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.Nd the entropy device
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.Sh DESCRIPTION
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The
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.Nm
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device accepts and reads data as any ordinary (and willing) file,
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but throws away any data written to it,
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and returns an endless supply of random bytes when read.
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.Pp
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The only purpose of writing data to
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.Nm
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is to perturb the internal state.
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This perturbation of the internal state
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is the only userland method of introducing
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extra entropy into the device.
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If the writer has superuser privilege,
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then closing the device after writing
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will make the internal generator reseed itself.
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This can be used for extra security,
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as it immediately introduces any/all new entropy
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into the PRNG.
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The
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.Nm
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device can be controlled with
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.Xr sysctl 8 .
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.Pp
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To see the devices' current settings, use the command line:
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.Pp
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.Dl sysctl kern.random
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.Pp
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which results in something like:
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.Pp
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.Bd -literal -offset indent
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kern.random.sys.seeded: 1
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kern.random.sys.burst: 20
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kern.random.sys.harvest.ethernet: 0
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kern.random.sys.harvest.point_to_point: 0
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kern.random.sys.harvest.interrupt: 0
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kern.random.yarrow.gengateinterval: 10
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kern.random.yarrow.bins: 10
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kern.random.yarrow.fastthresh: 100
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kern.random.yarrow.slowthresh: 160
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kern.random.yarrow.slowoverthresh: 2
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.Ed
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.Pp
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All settings are read/write.
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.Pp
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The
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.Va kern.random.sys.seeded
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variable indicates whether or not the
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.Nm
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device is in an acceptably secure state
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as a result of reseeding.
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If set to 0, the device will block (on read) until the next reseed
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(which can be from an explicit write,
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or as a result of entropy harvesting).
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A reseed will set the value to 1 (non-blocking).
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.Pp
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The
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.Va kern.random.sys.burst
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variable instructs the kernel thread
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that processes the harvest queue
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to
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.Xr tsleep 9
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briefly after that many events
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have been processed.
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This helps prevent the random device
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from being so compute-bound
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that it takes over all processing ability.
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A value of zero (0) is treated as
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.Em infinity ,
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and will only allow the kernel to pause
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if the queue is empty.
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Only values in the range
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.Bq 0..20
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are accepted.
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.Pp
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The
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.Va kern.random.sys.harvest.ethernet
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variable is used to select LAN traffic as an entropy source.
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A zero (0) value means that LAN traffic
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is not considered as an entropy source.
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Set the variable to one (1)
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if you wish to use LAN traffic for entropy harvesting.
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.Pp
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The
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.Va kern.random.sys.harvest.point_to_point
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variable is used to select serial line traffic as an entropy source.
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(Serial line traffic includes PPP, SLIP and all tun0 traffic.)
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A zero (0) value means such traffic
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is not considered as an entropy source.
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Set the variable to one (1)
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if you wish to use it for entropy harvesting.
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.Pp
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The
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.Va kern.random.sys.harvest.interrupt
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variable is used to select hardware interrupts
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as an entropy source.
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A zero (0) value means interrupts
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are not considered as an entropy source.
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Set the variable to one (1)
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if you wish to use them for entropy harvesting.
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All interrupt harvesting is setup by the
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individual device drivers.
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.Pp
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The other variables are explained in the paper describing the
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.Em Yarrow
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algorithm at
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.Pa http://www.counterpane.com/yarrow.html .
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.Pp
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These variables are all limited
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in terms of the values they may contain:
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.Bl -tag -width "kern.random.yarrow.gengateinterval" -compact -offset indent
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.It Va kern.random.yarrow.gengateinterval
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.Bq 4..64
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.It Va kern.random.yarrow.bins
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.Bq 2..16
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.It Va kern.random.yarrow.fastthresh
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.Bq 64..256
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.It Va kern.random.yarrow.slowthresh
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.Bq 64..256
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.It Va kern.random.yarrow.slowoverthresh
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.Bq 1..5
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.El
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.Pp
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Internal
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.Xr sysctl 3
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handlers force the above variables
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into the stated ranges.
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.Sh FILES
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.Bl -tag -width /dev/random
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.It Pa /dev/random
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.El
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.Sh SEE ALSO
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.Xr sysctl 8
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.Sh HISTORY
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A
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.Nm
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device appeared in
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.Fx 2.2 .
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The early version was taken from Theodore Ts'o's entropy driver for Linux.
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The current implementation,
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introduced in
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.Fx 5.0 ,
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is a complete rewrite by
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.An Mark R V Murray ,
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and is an implementation of the
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.Em Yarrow
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algorithm by Bruce Schneier,
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.Em et al .
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