1
1
<?xml version="1.0" encoding="UTF-8"?>
2
2
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3
3
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4
<!ENTITY TIMESTAMP "2021-02-03">
4
<!ENTITY TIMESTAMP "2012-01-01">
5
5
<!ENTITY % common SYSTEM "common.ent">
69
61
The computers run a small client program in the initial RAM disk
70
62
environment which will communicate with a server over a network.
71
63
All network communication is encrypted using TLS. The clients
72
are identified by the server using a TLS public key; each client
64
are identified by the server using an OpenPGP key; each client
73
65
has one unique to it. The server sends the clients an encrypted
74
66
password. The encrypted password is decrypted by the clients
75
using a separate OpenPGP key, and the password is then used to
67
using the same OpenPGP key, and the password is then used to
76
68
unlock the root file system, whereupon the computers can
77
69
continue booting normally.
81
73
<refsect1 id="introduction">
82
74
<title>INTRODUCTION</title>
84
<!-- This paragraph is a combination and paraphrase of two
85
quotes from the 1995 movie “The Usual Suspects”. -->
86
76
You know how it is. You’ve heard of it happening. The Man
87
77
comes and takes away your servers, your friends’ servers, the
88
78
servers of everybody in the same hosting facility. The servers
134
124
So, at boot time, the Mandos client will ask for its encrypted
135
data over the network, decrypt the data to get the password, use
136
the password to decrypt the root file system, and the client can
137
then continue booting.
125
data over the network, decrypt it to get the password, use it to
126
decrypt the root file, and continue booting.
140
129
Now, of course the initial RAM disk image is not on the
146
135
long, and will no longer give out the encrypted key. The timing
147
136
here is the only real weak point, and the method, frequency and
148
137
timeout of the server’s checking can be adjusted to any desired
152
141
(The encrypted keys on the Mandos server is on its normal file
204
193
No. The server only gives out the passwords to clients which
205
194
have <emphasis>in the TLS handshake</emphasis> proven that
206
they do indeed hold the private key corresponding to that
211
<refsect2 id="sniff">
212
<title>How about sniffing the network traffic and decrypting it
213
later by physically grabbing the Mandos client and using its
216
We only use <acronym>PFS</acronym> (Perfect Forward Security)
217
key exchange algorithms in TLS, which protects against this.
195
they do indeed hold the OpenPGP private key corresponding to
239
<refsect2 id="fakecheck">
240
<title>Faking checker results?</title>
218
<refsect2 id="fakeping">
219
<title>Faking ping replies?</title>
242
If the Mandos client does not have an SSH server, the default
243
is for the Mandos server to use
221
The default for the server is to use
244
222
<quote><literal>fping</literal></quote>, the replies to which
245
223
could be faked to eliminate the timeout. But this could
246
224
easily be changed to any shell command, with any security
247
measures you like. If the Mandos client
248
<emphasis>has</emphasis> an SSH server, the default
249
configuration (as generated by
250
<command>mandos-keygen</command> with the
251
<option>--password</option> option) is for the Mandos server
252
to use an <command>ssh-keyscan</command> command with strict
253
keychecking, which can not be faked. Alternatively, IPsec
254
could be used for the ping packets, making them secure.
225
measures you like. It could, for instance, be changed to an
226
SSH command with strict keychecking, which could not be faked.
227
Or IPsec could be used for the ping packets, making them
385
359
plugin requirements.
389
<refsect1 id="systemd">
390
<title>SYSTEMD</title>
392
More advanced startup systems like <citerefentry><refentrytitle
393
>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
394
already have their own plugin-like mechanisms for allowing
395
multiple agents to independently retrieve a password and deliver
396
it to the subsystem requesting a password to unlock the root
397
file system. On these systems, it would make no sense to run
398
<citerefentry><refentrytitle>plugin-runner</refentrytitle
399
><manvolnum>8mandos</manvolnum></citerefentry>, the plugins of
400
which would largely duplicate the work of (and conflict with)
401
the existing systems prompting for passwords.
404
As for <citerefentry><refentrytitle>systemd</refentrytitle
405
><manvolnum>1</manvolnum></citerefentry> in particular, it has
407
url="https://systemd.io/PASSWORD_AGENTS/">Password
408
Agents</ulink> system. Mandos uses this via its
409
<citerefentry><refentrytitle>password-agent</refentrytitle
410
><manvolnum>8mandos</manvolnum></citerefentry> program, which is
411
run instead of <citerefentry><refentrytitle
412
>plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum
413
></citerefentry> when <citerefentry><refentrytitle
414
>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
415
is used during system startup.
420
<xi:include href="bugs.xml"/>
423
363
<refsect1 id="see_also">
424
364
<title>SEE ALSO</title>
435
375
<manvolnum>8</manvolnum></citerefentry>,
436
376
<citerefentry><refentrytitle>plugin-runner</refentrytitle>
437
377
<manvolnum>8mandos</manvolnum></citerefentry>,
438
<citerefentry><refentrytitle>password-agent</refentrytitle>
439
<manvolnum>8mandos</manvolnum></citerefentry>,
440
378
<citerefentry><refentrytitle>mandos-client</refentrytitle>
441
379
<manvolnum>8mandos</manvolnum></citerefentry>,
442
380
<citerefentry><refentrytitle>password-prompt</refentrytitle>
added
removed
intro.xml
