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Document the random Casper service.
Reviewed by: bcr@ Differential Revision: https://reviews.freebsd.org/D14072
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lib/libcasper/services/cap_random/cap_random.3
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lib/libcasper/services/cap_random/cap_random.3
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.\" Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
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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 AUTHORS 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 AUTHORS 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 January 27, 2018
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.Dt CAP_RANDOM 3
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.Os
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.Sh NAME
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.Nm cap_random_buf
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.Nd "library for getting entropy in capability mode"
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.Sh LIBRARY
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.Lb libcap_random
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.Sh SYNOPSIS
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.In sys/nv.h
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.In libcasper.h
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.In casper/cap_random.h
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.Ft "int"
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.Fn cap_random_buf "cap_channel_t *chan" "void *buf" "size_t nbytes"
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.Sh DESCRIPTION
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The function
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.Fn cap_random_buf
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is equivalent to
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.Xr arc4random_buf 3
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except that the connection to the
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.Nm system.random
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service needs to be provided.
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.Sh EXAMPLES
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The following example first opens a capability to casper and then uses this
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capability to create the
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.Nm system.random
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casper service to obtain entropy.
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.Bd -literal
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cap_channel_t *capcas, *caprandom;
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unsigned char buf[16];
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int i;
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/* Open capability to Casper. */
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capcas = cap_init();
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if (capcas == NULL)
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err(1, "Unable to contact Casper");
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/* Enter capability mode sandbox. */
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if (cap_enter() < 0 && errno != ENOSYS)
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err(1, "Unable to enter capability mode");
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/* Use Casper capability to create capability to the system.random service. */
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caprandom = cap_service_open(capcas, "system.random");
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if (caprandom == NULL)
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err(1, "Unable to open system.random service");
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/* Close Casper capability, we don't need it anymore. */
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cap_close(capcas);
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/* Obtain entropy. */
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if (cap_random_buf(caprandom, buf, sizeof(buf)) < 0)
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err(1, "Unable to obtain entropy");
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for (i = 0; i < sizeof(buf); i++)
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printf("%.2x ", buf[i]);
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printf("\\n");
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.Ed
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.Sh SEE ALSO
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.Xr cap_enter 2 ,
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.Xr arc4random_buf 3 ,
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.Xr err 3 ,
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.Xr nv 3 ,
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.Xr capsicum 4
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.Sh AUTHORS
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The
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.Nm cap_random
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service was implemented by
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.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net
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under sponsorship from the FreeBSD Foundation.
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.Pp
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This manual page was written by
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.An Mariusz Zaborski Aq Mt oshogbo@FreeBSD.org .
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