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Document the random Casper service.

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Reviewed by:	bcr@
Differential Revision:	https://reviews.freebsd.org/D14072
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Mariusz Zaborski 2018-01-27 22:49:34 +00:00
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.\" Copyright (c) 2018 Mariusz Zaborski <oshogbo@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd January 27, 2018
.Dt CAP_RANDOM 3
.Os
.Sh NAME
.Nm cap_random_buf
.Nd "library for getting entropy in capability mode"
.Sh LIBRARY
.Lb libcap_random
.Sh SYNOPSIS
.In sys/nv.h
.In libcasper.h
.In casper/cap_random.h
.Ft "int"
.Fn cap_random_buf "cap_channel_t *chan" "void *buf" "size_t nbytes"
.Sh DESCRIPTION
The function
.Fn cap_random_buf
is equivalent to
.Xr arc4random_buf 3
except that the connection to the
.Nm system.random
service needs to be provided.
.Sh EXAMPLES
The following example first opens a capability to casper and then uses this
capability to create the
.Nm system.random
casper service to obtain entropy.
.Bd -literal
cap_channel_t *capcas, *caprandom;
unsigned char buf[16];
int i;
/* Open capability to Casper. */
capcas = cap_init();
if (capcas == NULL)
err(1, "Unable to contact Casper");
/* Enter capability mode sandbox. */
if (cap_enter() < 0 && errno != ENOSYS)
err(1, "Unable to enter capability mode");
/* Use Casper capability to create capability to the system.random service. */
caprandom = cap_service_open(capcas, "system.random");
if (caprandom == NULL)
err(1, "Unable to open system.random service");
/* Close Casper capability, we don't need it anymore. */
cap_close(capcas);
/* Obtain entropy. */
if (cap_random_buf(caprandom, buf, sizeof(buf)) < 0)
err(1, "Unable to obtain entropy");
for (i = 0; i < sizeof(buf); i++)
printf("%.2x ", buf[i]);
printf("\\n");
.Ed
.Sh SEE ALSO
.Xr cap_enter 2 ,
.Xr arc4random_buf 3 ,
.Xr err 3 ,
.Xr nv 3 ,
.Xr capsicum 4
.Sh AUTHORS
The
.Nm cap_random
service was implemented by
.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net
under sponsorship from the FreeBSD Foundation.
.Pp
This manual page was written by
.An Mariusz Zaborski Aq Mt oshogbo@FreeBSD.org .