63
67
<refname><command>&COMMANDNAME;</command></refname>
65
Client for <application>Mandos</application>
71
75
<command>&COMMANDNAME;</command>
73
<arg choice="plain"><option>--connect
74
<replaceable>ADDRESS</replaceable><literal>:</literal
75
><replaceable>PORT</replaceable></option></arg>
76
<arg choice="plain"><option>-c
77
<replaceable>ADDRESS</replaceable><literal>:</literal
78
><replaceable>PORT</replaceable></option></arg>
82
<arg choice="plain"><option>--interface
83
<replaceable>NAME</replaceable><arg rep='repeat'
84
>,<replaceable>NAME</replaceable></arg></option></arg>
85
<arg choice="plain"><option>-i <replaceable>NAME</replaceable
86
><arg rep='repeat'>,<replaceable>NAME</replaceable></arg
91
<arg choice="plain"><option>--pubkey
92
<replaceable>FILE</replaceable></option></arg>
93
<arg choice="plain"><option>-p
94
<replaceable>FILE</replaceable></option></arg>
98
<arg choice="plain"><option>--seckey
99
<replaceable>FILE</replaceable></option></arg>
100
<arg choice="plain"><option>-s
101
<replaceable>FILE</replaceable></option></arg>
105
<arg choice="plain"><option>--tls-privkey
106
<replaceable>FILE</replaceable></option></arg>
107
<arg choice="plain"><option>-t
108
<replaceable>FILE</replaceable></option></arg>
112
<arg choice="plain"><option>--tls-pubkey
113
<replaceable>FILE</replaceable></option></arg>
114
<arg choice="plain"><option>-T
115
<replaceable>FILE</replaceable></option></arg>
119
<option>--priority <replaceable>STRING</replaceable></option>
123
<option>--dh-bits <replaceable>BITS</replaceable></option>
127
<option>--dh-params <replaceable>FILE</replaceable></option>
131
<option>--delay <replaceable>SECONDS</replaceable></option>
135
<option>--retry <replaceable>SECONDS</replaceable></option>
139
<option>--network-hook-dir
140
<replaceable>DIR</replaceable></option>
144
<option>--debug</option>
148
<command>&COMMANDNAME;</command>
150
<arg choice="plain"><option>--help</option></arg>
151
<arg choice="plain"><option>-?</option></arg>
155
<command>&COMMANDNAME;</command>
156
<arg choice="plain"><option>--usage</option></arg>
159
<command>&COMMANDNAME;</command>
161
<arg choice="plain"><option>--version</option></arg>
162
<arg choice="plain"><option>-V</option></arg>
76
<arg choice='opt' rep='repeat'>OPTION</arg>
167
80
<refsect1 id="description">
168
81
<title>DESCRIPTION</title>
170
<command>&COMMANDNAME;</command> is a client program that
171
communicates with <citerefentry><refentrytitle
172
>mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>
173
to get a password. In slightly more detail, this client program
174
brings up network interfaces, uses the interfaces’ IPv6
175
link-local addresses to get network connectivity, uses Zeroconf
176
to find servers on the local network, and communicates with
177
servers using TLS with a raw public key to ensure authenticity
178
and confidentiality. This client program keeps running, trying
179
all servers on the network, until it receives a satisfactory
180
reply or a TERM signal. After all servers have been tried, all
181
servers are periodically retried. If no servers are found it
182
will wait indefinitely for new servers to appear.
185
The network interfaces are selected like this: If any interfaces
186
are specified using the <option>--interface</option> option,
187
those interface are used. Otherwise,
188
<command>&COMMANDNAME;</command> will use all interfaces that
189
are not loopback interfaces, are not point-to-point interfaces,
190
are capable of broadcasting and do not have the NOARP flag (see
191
<citerefentry><refentrytitle>netdevice</refentrytitle>
192
<manvolnum>7</manvolnum></citerefentry>). (If the
193
<option>--connect</option> option is used, point-to-point
194
interfaces and non-broadcast interfaces are accepted.) If any
195
used interfaces are not up and running, they are first taken up
196
(and later taken down again on program exit).
199
Before network interfaces are selected, all <quote>network
200
hooks</quote> are run; see <xref linkend="network-hooks"/>.
203
This program is not meant to be run directly; it is really meant
204
to be run by other programs in the initial
205
<acronym>RAM</acronym> disk environment; see <xref
206
linkend="overview"/>.
210
<refsect1 id="purpose">
211
<title>PURPOSE</title>
213
The purpose of this is to enable <emphasis>remote and unattended
214
rebooting</emphasis> of client host computer with an
215
<emphasis>encrypted root file system</emphasis>. See <xref
216
linkend="overview"/> for details.
220
<refsect1 id="options">
221
<title>OPTIONS</title>
223
This program is commonly not invoked from the command line; it
224
is normally started by another program as described in <xref
225
linkend="description"/>. Any command line options this program
226
accepts are therefore normally provided by the invoking program,
232
<term><option>--connect=<replaceable
233
>ADDRESS</replaceable><literal>:</literal><replaceable
234
>PORT</replaceable></option></term>
236
<replaceable>ADDRESS</replaceable><literal>:</literal
237
><replaceable>PORT</replaceable></option></term>
240
Do not use Zeroconf to locate servers. Connect directly
241
to only one specified <application>Mandos</application>
242
server. Note that an IPv6 address has colon characters in
243
it, so the <emphasis>last</emphasis> colon character is
244
assumed to separate the address from the port number.
247
Normally, Zeroconf would be used to locate Mandos servers,
248
in which case this option would only be used when testing
255
<term><option>--interface=<replaceable
256
>NAME</replaceable><arg rep='repeat'>,<replaceable
257
>NAME</replaceable></arg></option></term>
259
<replaceable>NAME</replaceable><arg rep='repeat'>,<replaceable
260
>NAME</replaceable></arg></option></term>
263
Comma separated list of network interfaces that will be
264
brought up and scanned for Mandos servers to connect to.
265
The default is the empty string, which will automatically
266
use all appropriate interfaces.
269
If the <option>--connect</option> option is used, and
270
exactly one interface name is specified (except
271
<quote><literal>none</literal></quote>), this specifies
272
the interface to use to connect to the address given.
275
Note that since this program will normally run in the
276
initial RAM disk environment, the interface must be an
277
interface which exists at that stage. Thus, the interface
278
can normally not be a pseudo-interface such as
279
<quote>br0</quote> or <quote>tun0</quote>; such interfaces
280
will not exist until much later in the boot process, and
281
can not be used by this program, unless created by a
282
<quote>network hook</quote> — see <xref
283
linkend="network-hooks"/>.
286
<replaceable>NAME</replaceable> can be the string
287
<quote><literal>none</literal></quote>; this will make
288
<command>&COMMANDNAME;</command> only bring up interfaces
289
specified <emphasis>before</emphasis> this string. This
290
is not recommended, and only meant for advanced users.
296
<term><option>--pubkey=<replaceable
297
>FILE</replaceable></option></term>
299
<replaceable>FILE</replaceable></option></term>
302
OpenPGP public key file name. The default name is
303
<quote><filename>/conf/conf.d/mandos/pubkey.txt</filename
310
<term><option>--seckey=<replaceable
311
>FILE</replaceable></option></term>
313
<replaceable>FILE</replaceable></option></term>
316
OpenPGP secret key file name. The default name is
317
<quote><filename>/conf/conf.d/mandos/seckey.txt</filename
324
<term><option>--tls-pubkey=<replaceable
325
>FILE</replaceable></option></term>
327
<replaceable>FILE</replaceable></option></term>
330
TLS raw public key file name. The default name is
331
<quote><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename
338
<term><option>--tls-privkey=<replaceable
339
>FILE</replaceable></option></term>
341
<replaceable>FILE</replaceable></option></term>
344
TLS secret key file name. The default name is
345
<quote><filename>/conf/conf.d/mandos/tls-privkey.pem</filename
352
<term><option>--priority=<replaceable
353
>STRING</replaceable></option></term>
355
<xi:include href="../mandos-options.xml"
356
xpointer="priority"/>
361
<term><option>--dh-bits=<replaceable
362
>BITS</replaceable></option></term>
365
Sets the number of bits to use for the prime number in the
366
TLS Diffie-Hellman key exchange. The default value is
367
selected automatically based on the GnuTLS security
368
profile set in its priority string. Note that if the
369
<option>--dh-params</option> option is used, the values
370
from that file will be used instead.
376
<term><option>--dh-params=<replaceable
377
>FILE</replaceable></option></term>
380
Specifies a PEM-encoded PKCS#3 file to read the parameters
381
needed by the TLS Diffie-Hellman key exchange from. If
382
this option is not given, or if the file for some reason
383
could not be used, the parameters will be generated on
384
startup, which will take some time and processing power.
385
Those using servers running under time, power or processor
386
constraints may want to generate such a file in advance
393
<term><option>--delay=<replaceable
394
>SECONDS</replaceable></option></term>
397
After bringing a network interface up, the program waits
398
for the interface to arrive in a <quote>running</quote>
399
state before proceeding. During this time, the kernel log
400
level will be lowered to reduce clutter on the system
401
console, alleviating any other plugins which might be
402
using the system console. This option sets the upper
403
limit of seconds to wait. The default is 2.5 seconds.
409
<term><option>--retry=<replaceable
410
>SECONDS</replaceable></option></term>
413
All Mandos servers are tried repeatedly until a password
414
is received. This value specifies, in seconds, how long
415
between each successive try <emphasis>for the same
416
server</emphasis>. The default is 10 seconds.
422
<term><option>--network-hook-dir=<replaceable
423
>DIR</replaceable></option></term>
426
Network hook directory. The default directory is
427
<quote><filename class="directory"
428
>/lib/mandos/network-hooks.d</filename></quote>.
434
<term><option>--debug</option></term>
437
Enable debug mode. This will enable a lot of output to
438
standard error about what the program is doing. The
439
program will still perform all other functions normally.
442
It will also enable debug mode in the Avahi and GnuTLS
443
libraries, making them print large amounts of debugging
450
<term><option>--help</option></term>
451
<term><option>-?</option></term>
454
Gives a help message about options and their meanings.
460
<term><option>--usage</option></term>
463
Gives a short usage message.
469
<term><option>--version</option></term>
470
<term><option>-V</option></term>
473
Prints the program version.
480
<refsect1 id="overview">
481
<title>OVERVIEW</title>
482
<xi:include href="../overview.xml"/>
484
This program is the client part. It is run automatically in an
485
initial <acronym>RAM</acronym> disk environment.
488
In an initial <acronym>RAM</acronym> disk environment using
489
<citerefentry><refentrytitle>systemd</refentrytitle>
490
<manvolnum>1</manvolnum></citerefentry>, this program is started
491
by the <application>Mandos</application> <citerefentry>
492
<refentrytitle>password-agent</refentrytitle>
493
<manvolnum>8mandos</manvolnum></citerefentry>, which in turn is
494
started automatically by the <citerefentry>
495
<refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum>
496
</citerefentry> <quote>Password Agent</quote> system.
499
In the case of a non-<citerefentry>
500
<refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum>
501
</citerefentry> environment, this program is started as a plugin
502
of the <application>Mandos</application> <citerefentry>
503
<refentrytitle>plugin-runner</refentrytitle>
504
<manvolnum>8mandos</manvolnum></citerefentry>, which runs in the
505
initial <acronym>RAM</acronym> disk environment because it is
506
specified as a <quote>keyscript</quote> in the <citerefentry>
507
<refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum>
508
</citerefentry> file.
511
This program could, theoretically, be used as a keyscript in
512
<filename>/etc/crypttab</filename>, but it would then be
513
impossible to enter a password for the encrypted root disk at
514
the console, since this program does not read from the console
519
<refsect1 id="exit_status">
520
<title>EXIT STATUS</title>
522
This program will exit with a successful (zero) exit status if a
523
server could be found and the password received from it could be
524
successfully decrypted and output on standard output. The
525
program will exit with a non-zero exit status only if a critical
526
error occurs. Otherwise, it will forever connect to any
527
discovered <application>Mandos</application> servers, trying to
528
get a decryptable password and print it.
532
<refsect1 id="environment">
533
<title>ENVIRONMENT</title>
536
<term><envar>MANDOSPLUGINHELPERDIR</envar></term>
539
This environment variable will be assumed to contain the
540
directory containing any helper executables. The use and
541
nature of these helper executables, if any, is purposely
548
This program does not use any other environment variables, not
549
even the ones provided by <citerefentry><refentrytitle
550
>cryptsetup</refentrytitle><manvolnum>8</manvolnum>
555
<refsect1 id="network-hooks">
556
<title>NETWORK HOOKS</title>
558
If a network interface like a bridge or tunnel is required to
559
find a Mandos server, this requires the interface to be up and
560
running before <command>&COMMANDNAME;</command> starts looking
561
for Mandos servers. This can be accomplished by creating a
562
<quote>network hook</quote> program, and placing it in a special
566
Before the network is used (and again before program exit), any
567
runnable programs found in the network hook directory are run
568
with the argument <quote><literal>start</literal></quote> or
569
<quote><literal>stop</literal></quote>. This should bring up or
570
down, respectively, any network interface which
571
<command>&COMMANDNAME;</command> should use.
573
<refsect2 id="hook-requirements">
574
<title>REQUIREMENTS</title>
576
A network hook must be an executable file, and its name must
577
consist entirely of upper and lower case letters, digits,
578
underscores, periods, and hyphens.
581
A network hook will receive one argument, which can be one of
586
<term><literal>start</literal></term>
589
This should make the network hook create (if necessary)
590
and bring up a network interface.
595
<term><literal>stop</literal></term>
598
This should make the network hook take down a network
599
interface, and delete it if it did not exist previously.
604
<term><literal>files</literal></term>
607
This should make the network hook print, <emphasis>one
608
file per line</emphasis>, all the files needed for it to
609
run. (These files will be copied into the initial RAM
610
filesystem.) Typical use is for a network hook which is
611
a shell script to print its needed binaries.
614
It is not necessary to print any non-executable files
615
already in the network hook directory, these will be
616
copied implicitly if they otherwise satisfy the name
622
<term><literal>modules</literal></term>
625
This should make the network hook print, <emphasis>on
626
separate lines</emphasis>, all the kernel modules needed
627
for it to run. (These modules will be copied into the
628
initial RAM filesystem.) For instance, a tunnel
630
<quote><literal>tun</literal></quote> module.
636
The network hook will be provided with a number of environment
641
<term><envar>MANDOSNETHOOKDIR</envar></term>
644
The network hook directory, specified to
645
<command>&COMMANDNAME;</command> by the
646
<option>--network-hook-dir</option> option. Note: this
647
should <emphasis>always</emphasis> be used by the
648
network hook to refer to itself or any files in the hook
649
directory it may require.
654
<term><envar>DEVICE</envar></term>
657
The network interfaces, as specified to
658
<command>&COMMANDNAME;</command> by the
659
<option>--interface</option> option, combined to one
660
string and separated by commas. If this is set, and
661
does not contain the interface a hook will bring up,
662
there is no reason for a hook to continue.
667
<term><envar>MODE</envar></term>
670
This will be the same as the first argument;
671
i.e. <quote><literal>start</literal></quote>,
672
<quote><literal>stop</literal></quote>,
673
<quote><literal>files</literal></quote>, or
674
<quote><literal>modules</literal></quote>.
679
<term><envar>VERBOSITY</envar></term>
682
This will be the <quote><literal>1</literal></quote> if
683
the <option>--debug</option> option is passed to
684
<command>&COMMANDNAME;</command>, otherwise
685
<quote><literal>0</literal></quote>.
690
<term><envar>DELAY</envar></term>
693
This will be the same as the <option>--delay</option>
694
option passed to <command>&COMMANDNAME;</command>. Is
695
only set if <envar>MODE</envar> is
696
<quote><literal>start</literal></quote> or
697
<quote><literal>stop</literal></quote>.
702
<term><envar>CONNECT</envar></term>
705
This will be the same as the <option>--connect</option>
706
option passed to <command>&COMMANDNAME;</command>. Is
707
only set if <option>--connect</option> is passed and
708
<envar>MODE</envar> is
709
<quote><literal>start</literal></quote> or
710
<quote><literal>stop</literal></quote>.
716
A hook may not read from standard input, and should be
717
restrictive in printing to standard output or standard error
718
unless <varname>VERBOSITY</varname> is
719
<quote><literal>1</literal></quote>.
724
<refsect1 id="files">
728
<term><filename>/conf/conf.d/mandos/pubkey.txt</filename
730
<term><filename>/conf/conf.d/mandos/seckey.txt</filename
734
OpenPGP public and private key files, in <quote>ASCII
735
Armor</quote> format. These are the default file names,
736
they can be changed with the <option>--pubkey</option> and
737
<option>--seckey</option> options.
742
<term><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename
744
<term><filename>/conf/conf.d/mandos/tls-privkey.pem</filename
748
Public and private raw key files, in <quote>PEM</quote>
749
format. These are the default file names, they can be
750
changed with the <option>--tls-pubkey</option> and
751
<option>--tls-privkey</option> options.
757
class="directory">/lib/mandos/network-hooks.d</filename></term>
760
Directory where network hooks are located. Change this
761
with the <option>--network-hook-dir</option> option. See
762
<xref linkend="network-hooks"/>.
771
<xi:include href="../bugs.xml"/>
774
<refsect1 id="example">
775
<title>EXAMPLE</title>
777
Note that normally, command line options will not be given
778
directly, but passed on via the program responsible for starting
779
this program; see <xref linkend="overview"/>.
783
Normal invocation needs no options, if the network interfaces
784
can be automatically determined:
787
<userinput>&COMMANDNAME;</userinput>
792
Search for Mandos servers (and connect to them) using one
796
<!-- do not wrap this line -->
797
<userinput>&COMMANDNAME; --interface eth1</userinput>
802
Run in debug mode, and use custom keys:
806
<!-- do not wrap this line -->
807
<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --tls-pubkey keydir/tls-pubkey.pem --tls-privkey keydir/tls-privkey.pem</userinput>
813
Run in debug mode, with custom keys, and do not use Zeroconf
814
to locate a server; connect directly to the IPv6 link-local
815
address <quote><systemitem class="ipaddress"
816
>fe80::aede:48ff:fe71:f6f2</systemitem></quote>, port 4711,
817
using interface eth2:
821
<!-- do not wrap this line -->
822
<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --tls-pubkey keydir/tls-pubkey.pem --tls-privkey keydir/tls-privkey.pem --connect fe80::aede:48ff:fe71:f6f2:4711 --interface eth2</userinput>
828
<refsect1 id="security">
829
<title>SECURITY</title>
831
This program assumes that it is set-uid to root, and will switch
832
back to the original (and presumably non-privileged) user and
833
group after bringing up the network interface.
836
To use this program for its intended purpose (see <xref
837
linkend="purpose"/>), the password for the root file system will
838
have to be given out to be stored in a server computer, after
839
having been encrypted using an OpenPGP key. This encrypted data
840
which will be stored in a server can only be decrypted by the
841
OpenPGP key, and the data will only be given out to those
842
clients who can prove they actually have that key. This key,
843
however, is stored unencrypted on the client side in its initial
844
<acronym>RAM</acronym> disk image file system. This is normally
845
readable by all, but this is normally fixed during installation
846
of this program; file permissions are set so that no-one is able
850
The only remaining weak point is that someone with physical
851
access to the client hard drive might turn off the client
852
computer, read the OpenPGP and TLS keys directly from the hard
853
drive, and communicate with the server. To safeguard against
854
this, the server is supposed to notice the client disappearing
855
and stop giving out the encrypted data. Therefore, it is
856
important to set the timeout and checker interval values tightly
857
on the server. See <citerefentry><refentrytitle
858
>mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
861
It will also help if the checker program on the server is
862
configured to request something from the client which can not be
863
spoofed by someone else on the network, like SSH server key
864
fingerprints, and unlike unencrypted <acronym>ICMP</acronym>
865
echo (<quote>ping</quote>) replies.
868
<emphasis>Note</emphasis>: This makes it completely insecure to
869
have <application >Mandos</application> clients which dual-boot
870
to another operating system which is <emphasis>not</emphasis>
871
trusted to keep the initial <acronym>RAM</acronym> disk image
876
<refsect1 id="see_also">
877
<title>SEE ALSO</title>
879
<citerefentry><refentrytitle>intro</refentrytitle>
880
<manvolnum>8mandos</manvolnum></citerefentry>,
881
<citerefentry><refentrytitle>cryptsetup</refentrytitle>
882
<manvolnum>8</manvolnum></citerefentry>,
883
<citerefentry><refentrytitle>crypttab</refentrytitle>
884
<manvolnum>5</manvolnum></citerefentry>,
885
<citerefentry><refentrytitle>mandos</refentrytitle>
886
<manvolnum>8</manvolnum></citerefentry>,
887
<citerefentry><refentrytitle>password-agent</refentrytitle>
888
<manvolnum>8mandos</manvolnum></citerefentry>,
889
<citerefentry><refentrytitle>plugin-runner</refentrytitle>
890
<manvolnum>8mandos</manvolnum></citerefentry>
895
<ulink url="http://www.zeroconf.org/">Zeroconf</ulink>
899
Zeroconf is the network protocol standard used for finding
900
Mandos servers on the local network.
906
<ulink url="https://www.avahi.org/">Avahi</ulink>
910
Avahi is the library this program calls to find Zeroconf
917
<ulink url="https://www.gnutls.org/">GnuTLS</ulink>
921
GnuTLS is the library this client uses to implement TLS for
922
communicating securely with the server, and at the same time
923
send the public key to the server.
929
<ulink url="https://www.gnupg.org/related_software/gpgme/"
934
GPGME is the library used to decrypt the OpenPGP data sent
941
RFC 4291: <citetitle>IP Version 6 Addressing
942
Architecture</citetitle>
947
<term>Section 2.2: <citetitle>Text Representation of
948
Addresses</citetitle></term>
949
<listitem><para/></listitem>
952
<term>Section 2.5.5.2: <citetitle>IPv4-Mapped IPv6
953
Address</citetitle></term>
954
<listitem><para/></listitem>
957
<term>Section 2.5.6, <citetitle>Link-Local IPv6 Unicast
958
Addresses</citetitle></term>
961
This client uses IPv6 link-local addresses, which are
962
immediately usable since a link-local addresses is
963
automatically assigned to a network interface when it
973
RFC 5246: <citetitle>The Transport Layer Security (TLS)
974
Protocol Version 1.2</citetitle>
978
TLS 1.2 is the protocol implemented by GnuTLS.
984
RFC 4880: <citetitle>OpenPGP Message Format</citetitle>
988
The data received from the server is binary encrypted
995
RFC 7250: <citetitle>Using Raw Public Keys in Transport
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Layer Security (TLS) and Datagram Transport Layer Security
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This is implemented by GnuTLS in version 3.6.6 and is, if
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present, used by this program so that raw public keys can be
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RFC 6091: <citetitle>Using OpenPGP Keys for Transport Layer
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Security</citetitle>
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This is implemented by GnuTLS before version 3.6.0 and is,
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if present, used by this program so that OpenPGP keys can be
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<command>&COMMANDNAME;</command> is a mandos plugin that works
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like a client program that through avahi detects mandos servers,
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sets up a gnutls connect and request a encrypted password. Any
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passwords given is automaticly decrypted and passed to
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<term><literal>-c</literal>, <literal>--connect=<replaceable>
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IP</replaceable></literal></term>
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Connect directly to a sepcified mandos server
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<term><literal>-d</literal>, <literal>--keydir=<replaceable>
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KEYDIR</replaceable></literal></term>
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Directory where the openpgp keyring is
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<term><literal>-i</literal>, <literal>--interface=
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<replaceable>INTERFACE</replaceable></literal></term>
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Interface that Avahi will conntect through
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<term><literal>-p</literal>, <literal>--pubkey=<replaceable>
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PUBKEY</replaceable></literal></term>
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Public openpgp key for gnutls authentication
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<term><literal>-s</literal>, <literal>--seckey=<replaceable>
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SECKEY</replaceable></literal></term>
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Secret openpgp key for gnutls authentication
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<term><literal>--priority=<replaceable>PRIORITY</replaceable>
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<term><literal>--dh-bits=<replaceable>BITS</replaceable>
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dh-bits to use in gnutls communication
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<term><literal>--debug</literal></term>
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<term><literal>-?</literal>, <literal>--help</literal></term>
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<term><literal>--usage</literal></term>
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Gives a short usage message
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<term><literal>-V</literal>, <literal>--version</literal></term>
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Prints the program version
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