103 lines
3.0 KiB
Groff
103 lines
3.0 KiB
Groff
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.\"
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.\" Copyright (c) 2002 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 February 6, 2002
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.Dt RANDOM_HARVEST 9
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.Os FreeBSD
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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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.Fd #include <sys/random.h>
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.Ft void
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.Fn random_harvest "void *entropy" "u_int size" "u_int bits" "u_int frac" "enum esource source"
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.Sh DESCRIPTION
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The
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.Nm
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function is 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 a pointer (to no more than 16 bytes) of
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the ``random'' data in
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.Ar entropy.
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The argument
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.Ar size
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contains the number of bytes pointed to.
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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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.Ar bits
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or
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.Ar frac .
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If the estimated number of bits per sample is an integer, then
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.Ar bits
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is used, and
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.Ar frac is 0.
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Otherwise,
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for low-entropy samples,
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``fractional'' entropy can be supplied in
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.Ar frac
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(This is considered to be
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.Ar frac /
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1024 bits of entropy).
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The
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.Ar source
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is chosen from
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.Dv RANDOM_WRITE ,
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.Dv RANDOM_KEYBOARD ,
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.Dv RANDOM_MOUSE ,
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.Dv RANDOM_NET
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and
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.Dv RANDOM_INTERRUPT
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and is used to indicate the source of the entropy.
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.Pp
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Interrupt harvesting has been 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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.Fn BUS_SETUP_INTR
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or
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.Fn bus_setup_intr ,
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then it is only necessary to
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include the INTR_ENTROPY bit in the
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.Ar flags
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argument to have that interrupt source
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be used for entropy harvesting.
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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 AUTHOR
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The
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.Fx
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.Pa /dev/random
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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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