148 lines
3.5 KiB
Groff
148 lines
3.5 KiB
Groff
.\"
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.\" Copyright (c) 2002-2015 Mark R V Murray
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.\" 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 ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" 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 July 13, 2015
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.Dt RANDOM_HARVEST 9
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.Os
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.Sh NAME
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.Nm random_harvest
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.Nd gather entropy from the kernel for the entropy device
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/random.h
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.Ft void
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.Fo random_harvest_direct
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.Fa "void *entropy"
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.Fa "u_int size"
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.Fa "u_int bits"
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.Fa "enum esource source"
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.Fc
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.Ft void
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.Fo random_harvest_fast
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.Fa "void *entropy"
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.Fa "u_int size"
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.Fa "u_int bits"
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.Fa "enum esource source"
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.Fc
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.Ft void
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.Fo random_harvest_queue
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.Fa "void *entropy"
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.Fa "u_int size"
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.Fa "u_int bits"
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.Fa "enum esource source"
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.Fc
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.Sh DESCRIPTION
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The
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.Fn random_harvest_*
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functions are used by device drivers
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and other kernel processes to pass data
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that is considered (at least partially) stochastic
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to the entropy device.
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.Pp
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The caller should pass
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a pointer pointing to the
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.Dq random
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data in
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.Fa entropy .
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The argument
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.Fa size
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contains the number of bytes pointed to.
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The
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.Fa source
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is chosen from one of
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the values enumerated in
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.Pa sys/dev/random.h .
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and is used to indicate the source of the entropy.
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.Pp
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The
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.Fo random_harvest_direct
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.Fc
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variant is used
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for early harvesting
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before any multitasking
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is enabled.
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.Pp
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The
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.Fn random_harvest_fast
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variant is used
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by sources that
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should not take
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a performance hit
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from harvesting,
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as they are high-rate
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sources.
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Some entropy is sacrificed,
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but the high rate of supply
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will compensate for this.
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.Pp
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The
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.Fn random_harvest_queue
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variant is used
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for general harvesting
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and is the default
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choice for most entropy sources
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such as interrupts
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or console events.
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.Pp
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The
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.Fa bits
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argument is only used
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by the deprecated Yarrow algorithm.
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For compatibility,
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the caller should
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.Em "very conservatively"
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estimate the number of random bits
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in the sample,
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and pass this in
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.Fa bits .
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.Pp
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Interrupt harvesting has been
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in part simplified
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for the kernel programmer.
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If a device driver registers an interrupt handler
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with
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.Xr BUS_SETUP_INTR 9
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or
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.Xr bus_setup_intr 9 ,
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then it is only necessary to
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include the
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.Dv INTR_ENTROPY
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bit in the
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.Fa flags
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argument to have that interrupt source
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be used for entropy harvesting.
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This should be done wherever practicable.
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.Sh SEE ALSO
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.Xr random 4 ,
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.Xr BUS_SETUP_INTR 9
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.Sh AUTHORS
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The
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.Fx
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.Xr random 4
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entropy device and supporting documentation was written by
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.An Mark R V Murray .
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