1
<?xml version="1.0" encoding="UTF-8"?>
2
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
4
<!ENTITY TIMESTAMP "2015-03-08">
5
<!ENTITY % common SYSTEM "common.ent">
9
<refentry xmlns:xi="http://www.w3.org/2001/XInclude">
11
<title>Mandos Manual</title>
12
<!-- NWalsh’s docbook scripts use this to generate the footer: -->
13
<productname>Mandos</productname>
14
<productnumber>&version;</productnumber>
15
<date>&TIMESTAMP;</date>
18
<firstname>Björn</firstname>
19
<surname>Påhlsson</surname>
21
<email>belorn@recompile.se</email>
25
<firstname>Teddy</firstname>
26
<surname>Hogeborn</surname>
28
<email>teddy@recompile.se</email>
35
<holder>Teddy Hogeborn</holder>
36
<holder>Björn Påhlsson</holder>
38
<xi:include href="legalnotice.xml"/>
42
<refentrytitle>intro</refentrytitle>
43
<manvolnum>8mandos</manvolnum>
47
<refname>intro</refname>
49
Introduction to the Mandos system
53
<refsect1 id="description">
54
<title>DESCRIPTION</title>
56
This is the the Mandos system, which allows computers to have
57
encrypted root file systems and at the same time be capable of
58
remote and/or unattended reboots.
61
The computers run a small client program in the initial RAM disk
62
environment which will communicate with a server over a network.
63
All network communication is encrypted using TLS. The clients
64
are identified by the server using an OpenPGP key; each client
65
has one unique to it. The server sends the clients an encrypted
66
password. The encrypted password is decrypted by the clients
67
using the same OpenPGP key, and the password is then used to
68
unlock the root file system, whereupon the computers can
69
continue booting normally.
73
<refsect1 id="introduction">
74
<title>INTRODUCTION</title>
76
You know how it is. You’ve heard of it happening. The Man
77
comes and takes away your servers, your friends’ servers, the
78
servers of everybody in the same hosting facility. The servers
79
of their neighbors, and their neighbors’ friends. The servers
80
of people who owe them money. And like
81
<emphasis>that</emphasis>, they’re gone. And you doubt you’ll
85
That is why your servers have encrypted root file systems.
86
However, there’s a downside. There’s no going around it:
87
rebooting is a pain. Dragging out that rarely-used keyboard and
88
screen and unraveling cables behind your servers to plug them in
89
to type in that password is messy, especially if you have many
90
servers. There are some people who do clever things like using
91
serial line consoles and daisy-chain it to the next server, and
92
keep all the servers connected in a ring with serial cables,
93
which will work, if your servers are physically close enough.
94
There are also other out-of-band management solutions, but with
95
<emphasis>all</emphasis> these, you still have to be on hand and
96
manually type in the password at boot time. Otherwise the
97
server just sits there, waiting for a password.
100
Wouldn’t it be great if you could have the security of encrypted
101
root file systems and still have servers that could boot up
102
automatically if there was a short power outage while you were
103
asleep? That you could reboot at will, without having someone
104
run over to the server to type in the password?
107
Well, with Mandos, you (almost) can! The gain in convenience
108
will only be offset by a small loss in security. The setup is
112
The server will still have its encrypted root file system. The
113
password to this file system will be stored on another computer
114
(henceforth known as the Mandos server) on the same local
115
network. The password will <emphasis>not</emphasis> be stored
116
in plaintext, but encrypted with OpenPGP. To decrypt this
117
password, a key is needed. This key (the Mandos client key)
118
will not be stored there, but back on the original server
119
(henceforth known as the Mandos client) in the initial RAM disk
120
image. Oh, and all network Mandos client/server communications
121
will be encrypted, using TLS (SSL).
124
So, at boot time, the Mandos client will ask for its encrypted
125
data over the network, decrypt it to get the password, use it to
126
decrypt the root file, and continue booting.
129
Now, of course the initial RAM disk image is not on the
130
encrypted root file system, so anyone who had physical access
131
could take the Mandos client computer offline and read the disk
132
with their own tools to get the authentication keys used by a
133
client. <emphasis>But</emphasis>, by then the Mandos server
134
should notice that the original server has been offline for too
135
long, and will no longer give out the encrypted key. The timing
136
here is the only real weak point, and the method, frequency and
137
timeout of the server’s checking can be adjusted to any desired
141
(The encrypted keys on the Mandos server is on its normal file
142
system, so those are safe, provided the root file system of
143
<emphasis>that</emphasis> server is encrypted.)
148
<title>FREQUENTLY ASKED QUESTIONS</title>
150
Couldn’t the security be defeated by…
152
<refsect2 id="quick">
153
<title>Grabbing the Mandos client key from the
154
initrd <emphasis>really quickly</emphasis>?</title>
156
This, as mentioned above, is the only real weak point. But if
157
you set the timing values tight enough, this will be really
158
difficult to do. An attacker would have to physically
159
disassemble the client computer, extract the key from the
160
initial RAM disk image, and then connect to a <emphasis>still
161
online</emphasis> Mandos server to get the encrypted key, and do
162
all this <emphasis>before</emphasis> the Mandos server timeout
163
kicks in and the Mandos server refuses to give out the key to
167
Now, as the typical procedure seems to be to barge in and turn
168
off and grab <emphasis>all</emphasis> computers, to maybe look
169
at them months later, this is not likely. If someone does that,
170
the whole system <emphasis>will</emphasis> lock itself up
171
completely, since Mandos servers are no longer running.
174
For sophisticated attackers who <emphasis>could</emphasis> do
175
the clever thing, <emphasis>and</emphasis> had physical access
176
to the server for enough time, it would be simpler to get a key
177
for an encrypted file system by using hardware memory scanners
178
and reading it right off the memory bus.
182
<refsect2 id="replay">
183
<title>Replay attacks?</title>
185
Nope, the network stuff is all done over TLS, which provides
186
protection against that.
191
<title>Man-in-the-middle?</title>
193
No. The server only gives out the passwords to clients which
194
have <emphasis>in the TLS handshake</emphasis> proven that
195
they do indeed hold the OpenPGP private key corresponding to
200
<refsect2 id="sniff">
201
<title>How about sniffing the network traffic and decrypting it
202
later by physically grabbing the Mandos client and using its
205
We only use <acronym>PFS</acronym> (Perfect Forward Security)
206
key exchange algorithms in TLS, which protects against this.
210
<refsect2 id="physgrab">
211
<title>Physically grabbing the Mandos server computer?</title>
213
You could protect <emphasis>that</emphasis> computer the
214
old-fashioned way, with a must-type-in-the-password-at-boot
215
method. Or you could have two computers be the Mandos server
219
Multiple Mandos servers can coexist on a network without any
220
trouble. They do not clash, and clients will try all
221
available servers. This means that if just one reboots then
222
the other can bring it back up, but if both reboot at the same
223
time they will stay down until someone types in the password
228
<refsect2 id="fakecheck">
229
<title>Faking checker results?</title>
231
If the Mandos client does not have an SSH server, the default
232
is for the Mandos server to use
233
<quote><literal>fping</literal></quote>, the replies to which
234
could be faked to eliminate the timeout. But this could
235
easily be changed to any shell command, with any security
236
measures you like. If the Mandos client
237
<emphasis>has</emphasis> an SSH server, the default
238
configuration (as generated by
239
<command>mandos-keygen</command> with the
240
<option>--password</option> option) is for the Mandos server
241
to use an <command>ssh-keyscan</command> command with strict
242
keychecking, which can not be faked. Alternatively, IPsec
243
could be used for the ping packets, making them secure.
248
<refsect1 id="security">
249
<title>SECURITY</title>
251
So, in summary: The only weakness in the Mandos system is from
257
The power to come in and physically take your servers,
258
<emphasis>and</emphasis>
263
The cunning and patience to do it carefully, one at a time,
264
and <emphasis>quickly</emphasis>, faking Mandos
265
client/server responses for each one before the timeout.
270
While there are some who may be threatened by people who have
271
<emphasis>both</emphasis> these attributes, they do not,
272
probably, constitute the majority.
275
If you <emphasis>do</emphasis> face such opponents, you must
276
figure that they could just as well open your servers and read
277
the file system keys right off the memory by running wires to
281
What Mandos is designed to protect against is
282
<emphasis>not</emphasis> such determined, focused, and competent
283
attacks, but against the early morning knock on your door and
284
the sudden absence of all the servers in your server room.
285
Which it does nicely.
289
<refsect1 id="plugins">
290
<title>PLUGINS</title>
292
In the early designs, the
293
<citerefentry><refentrytitle>mandos-client</refentrytitle
294
><manvolnum>8mandos</manvolnum></citerefentry> program (which
295
retrieves a password from the Mandos server) also prompted for a
296
password on the terminal, in case a Mandos server could not be
297
found. Other ways of retrieving a password could easily be
298
envisoned, but this multiplicity of purpose was seen to be too
299
complex to be a viable way to continue. Instead, the original
300
program was separated into <citerefentry><refentrytitle
301
>mandos-client</refentrytitle><manvolnum>8mandos</manvolnum
302
></citerefentry> and <citerefentry><refentrytitle
303
>password-prompt</refentrytitle><manvolnum>8mandos</manvolnum
304
></citerefentry>, and a <citerefentry><refentrytitle
305
>plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum
306
></citerefentry> exist to run them both in parallel, allowing
307
the first successful plugin to provide the password. This
308
opened up for any number of additional plugins to run, all
309
competing to be the first to find a password and provide it to
313
Four additional plugins are provided:
318
<citerefentry><refentrytitle>plymouth</refentrytitle>
319
<manvolnum>8mandos</manvolnum></citerefentry>
323
This prompts for a password when using <citerefentry>
324
<refentrytitle>plymouth</refentrytitle><manvolnum
325
>8</manvolnum></citerefentry>.
331
<citerefentry><refentrytitle>usplash</refentrytitle>
332
<manvolnum>8mandos</manvolnum></citerefentry>
336
This prompts for a password when using <citerefentry>
337
<refentrytitle>usplash</refentrytitle><manvolnum
338
>8</manvolnum></citerefentry>.
344
<citerefentry><refentrytitle>splashy</refentrytitle>
345
<manvolnum>8mandos</manvolnum></citerefentry>
349
This prompts for a password when using <citerefentry>
350
<refentrytitle>splashy</refentrytitle><manvolnum
351
>8</manvolnum></citerefentry>.
357
<citerefentry><refentrytitle>askpass-fifo</refentrytitle>
358
<manvolnum>8mandos</manvolnum></citerefentry>
362
To provide compatibility with the "askpass" program from
363
cryptsetup, this plugin listens to the same FIFO as
370
More plugins can easily be written and added by the system
371
administrator; see the section called "WRITING PLUGINS" in
372
<citerefentry><refentrytitle>plugin-runner</refentrytitle>
373
<manvolnum>8mandos</manvolnum></citerefentry> to learn the
378
<refsect1 id="see_also">
379
<title>SEE ALSO</title>
381
<citerefentry><refentrytitle>mandos</refentrytitle>
382
<manvolnum>8</manvolnum></citerefentry>,
383
<citerefentry><refentrytitle>mandos.conf</refentrytitle>
384
<manvolnum>5</manvolnum></citerefentry>,
385
<citerefentry><refentrytitle>mandos-clients.conf</refentrytitle>
386
<manvolnum>5</manvolnum></citerefentry>,
387
<citerefentry><refentrytitle>mandos-ctl</refentrytitle>
388
<manvolnum>8</manvolnum></citerefentry>,
389
<citerefentry><refentrytitle>mandos-monitor</refentrytitle>
390
<manvolnum>8</manvolnum></citerefentry>,
391
<citerefentry><refentrytitle>plugin-runner</refentrytitle>
392
<manvolnum>8mandos</manvolnum></citerefentry>,
393
<citerefentry><refentrytitle>mandos-client</refentrytitle>
394
<manvolnum>8mandos</manvolnum></citerefentry>,
395
<citerefentry><refentrytitle>password-prompt</refentrytitle>
396
<manvolnum>8mandos</manvolnum></citerefentry>,
397
<citerefentry><refentrytitle>plymouth</refentrytitle>
398
<manvolnum>8mandos</manvolnum></citerefentry>,
399
<citerefentry><refentrytitle>usplash</refentrytitle>
400
<manvolnum>8mandos</manvolnum></citerefentry>,
401
<citerefentry><refentrytitle>splashy</refentrytitle>
402
<manvolnum>8mandos</manvolnum></citerefentry>,
403
<citerefentry><refentrytitle>askpass-fifo</refentrytitle>
404
<manvolnum>8mandos</manvolnum></citerefentry>,
405
<citerefentry><refentrytitle>mandos-keygen</refentrytitle>
406
<manvolnum>8</manvolnum></citerefentry>
411
<ulink url="http://www.recompile.se/mandos">Mandos</ulink>
415
The Mandos home page.
422
<!-- Local Variables: -->
423
<!-- time-stamp-start: "<!ENTITY TIMESTAMP [\"']" -->
424
<!-- time-stamp-end: "[\"']>" -->
425
<!-- time-stamp-format: "%:y-%02m-%02d" -->
added
removed
intro.xml
