gvpe/doc/gvpe.5.pod

=head1 NAME

GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.

=head1 DESCRIPTION

GVPE is a suite designed to provide a virtual private network for multiple
nodes over an untrusted network. This document first gives an introduction
to VPNs in general and then describes the specific implementation of GVPE.

=head2 WHAT IS A VPN?

VPN is an acronym, it stands for:

=over 4

=item Virtual

Virtual means that no physical network is created (of course), but a
network is I<emulated> by creating multiple tunnels between the member
nodes by encapsulating and sending data over another transport network.

Usually the emulated network is a normal IP or Ethernet, and the transport
network is the Internet. However, using a VPN system like GVPE to connect
nodes over other untrusted networks such as Wireless LAN is not uncommon.

=item Private

Private means that non-participating nodes cannot decode ("sniff)" nor
inject ("spoof") packets. This means that nodes can be connected over
untrusted networks such as the public Internet without fear of being
eavesdropped while at the same time being able to trust data sent by other
nodes.

In the case of GVPE, even participating nodes cannot sniff packets
send to other nodes or spoof packets as if sent from other nodes, so
communications between any two nodes is private to those two nodes.

=item Network

Network means that more than two parties can participate in the network,
so for instance it's possible to connect multiple branches of a company
into a single network. Many so-called "VPN" solutions only create
point-to-point tunnels, which in turn can be used to build larger
networks.

GVPE provides a true multi-point network in which any number of nodes (at
least a few dozen in practise, the theoretical limit is 4095 nodes) can
participate.

=back

=head2 GVPE DESIGN GOALS

=over 4

=item SIMPLE DESIGN

Cipher, HMAC algorithms and other key parameters must be selected
at compile time - this makes it possible to only link in algorithms
you actually need. It also makes the crypto part of the source very
transparent and easy to inspect, and last not least this makes it possible
to hardcode the layout of all packets into the binary. GVPE goes a step
further and internally reserves blocks of the same length for all packets,
which virtually removes all possibilities of buffer overflows, as there is
only a single type of buffer and it's always of fixed length.

=item EASY TO SETUP

A few lines of config (the config file is shared unmodified between all
hosts) and generating an RSA key-pair on each node suffices to make it
work.

=item MAC-BASED SECURITY

Since every host has it's own private key, other hosts cannot spoof
traffic from this host. That makes it possible to filter packet by MAC
address, e.g. to ensure that packets from a specific IP address come, in
fact, from a specific host that is associated with that IP and not from
another host.

=back

=head1 PROGRAMS

Gvpe comes with two programs: one daemon (C<gvpe>) and one control program
(C<gvpectrl>).

=over 4

=item gvpectrl

This program is used to generate the keys, check and give an overview of of the
configuration and to control the daemon (restarting etc.).

=item gvpe

This is the daemon used to establish and maintain connections to the other
network nodes. It should be run on the gateway of each VPN subnet.

=back

=head1 COMPILETIME CONFIGURATION

Please have a look at the C<gvpe.osdep(5)> manpage for platform-specific
information.

Gvpe hardcodes most encryption parameters. While this reduces flexibility,
it makes the program much simpler and helps making buffer overflows
impossible under most circumstances.

Here are a few recipes for compiling your gvpe, showing the extremes
(fast, small, insecure OR slow, large, more secure), between which you
should choose:

=head2 AS LOW PACKET OVERHEAD AS POSSIBLE

   ./configure --enable-hmac-length=4 --enable-rand-length=0

Minimize the header overhead of VPN packets (the above will result in
only 4 bytes of overhead over the raw ethernet frame). This is a insecure
configuration because a HMAC length of 4 makes collision attacks almost
trivial.

=head2 MINIMIZE CPU TIME REQUIRED

   ./configure --enable-cipher=bf --enable-digest=md4

Use the fastest cipher and digest algorithms currently available in
gvpe. MD4 has been broken and is quite insecure, though, so using another
digest algorithm is recommended.

=head2 MAXIMIZE SECURITY

   ./configure --enable-hmac-length=16 --enable-rand-length=12 --enable-digest=ripemd610

This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12
would also be pretty secure ;) and will additionally prefix each packet
with 12 bytes of random data.

In general, remember that AES-128 seems to be as secure but faster than
AES-192 or AES-256, more randomness helps against sniffing and a longer
HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
are consecutively better, and Blowfish is a fast cipher (and also quite
secure).

=head1 HOW TO SET UP A SIMPLE VPN

In this section I will describe how to get a simple VPN consisting of
three hosts up and running.

=head2 STEP 1: configuration

First you have to create a daemon configuration file and put it into the
configuration directory. This is usually C</etc/gvpe>, depending on how you
configured gvpe, and can be overwritten using the C<-c> command line switch.

Put the following lines into C</etc/gvpe/gvpe.conf>:

   udp-port = 50000 # the external port to listen on (configure your firewall)
   mtu = 1400       # minimum MTU of all outgoing interfaces on all hosts
   ifname = vpn0    # the local network device name

   node = first     # just a nickname
   hostname = first.example.net # the DNS name or IP address of the host

   node = second
   hostname = 133.55.82.9

   node = third
   hostname = third.example.net

The only other file necessary is the C<if-up> script that initializes the
virtual ethernet interface on the local host. Put the following lines into
C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):

   #!/bin/sh
   ip link set $IFNAME address $MAC mtu $MTU up
   [ $NODENAME = first  ] && ip addr add 10.0.1.1 dev $IFNAME
   [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
   [ $NODENAME = third  ] && ip addr add 10.0.3.1 dev $IFNAME
   ip route add 10.0.0.0/16 dev $IFNAME

This script will give each node a different IP address in the C<10.0/16>
network.  The internal network (if gvpe runs on a router) should then be
set to a subset of that network, e.g.  C<10.0.1.0/24> on node C<first>,
C<10.0.2.0/24> on node C<second>, and so on.

By enabling routing on the gateway host that runs C<gvpe> all nodes will
be able to reach the other nodes. You can, of course, also use proxy ARP
or other means of pseudo-bridging, or (best) full routing - the choice is
yours.

=head2 STEP 2: create the RSA key pair for each node

Next you have to generate the RSA keys for the nodes. While you can set
up GVPE so you can generate all keys on a single host and centrally
distribute all keys, it is safer to generate the key for each node on the
node, so that the secret/private key does not have to be copied over the
network.

To do so, run the following command to generate a key pair:

   gvpectrl -c /etc/gvpe -g nodekey

This will create two files, F<nodekey> and F<nodekey.privkey>. The former
should be copied to F<< /etc/gvpe/pubkey/I<nodename> >> on the host where
your config file is (you will have to create the F<pubkey> directory
first):

   scp nodekey confighost:/etc/gvpe/pubkey/nodename

The private key F<nodekey.privkey> should be moved to F</etc/gvpe/hostkey>:

   mkdir -p /etc/gvpe
   mv nodekey.privkey /etc/gvpe/hostkey

=head2 STEP 3: distribute the config files to all nodes

Now distribute the config files and public keys to the other nodes.

The example uses rsync-over-ssh to copy the config file and all the public
keys:

   rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkey
   rsync -avzessh /etc/gvpe 133.55.82.9:/etc/.       --exclude hostkey
   rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkey

You should now check the configuration by issuing the command C<gvpectrl
-c /etc/gvpe -s> on each node and verify it's output.

=head2 STEP 4: starting gvpe

You should then start gvpe on each node by issuing a command like:

   gvpe -D -l info first # first is the nodename

This will make the gvpe daemon stay in foreground. You should then see
"connection established" messages. If you don't see them check your
firewall and routing (use tcpdump ;).

If this works you should check your networking setup by pinging various
endpoints.

To make gvpe run more permanently you can either run it as a daemon (by
starting it without the C<-D> switch), or, much better, from your inittab
or equivalent. I use a line like this on all my systems:

   t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1

=head2 STEP 5: enjoy

... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
will make it try to connect to all other nodes again. If you run it from
inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will
kill the daemon, start it again, making it read it's configuration files
again.

To run the GVPE daemon permanently, you can either add it to your SysV
F<inittab>, e.g.:

   t1:2345:respawn:/bin/sh -c "exec nice -n-20 /path/to/gvpe -D node >/var/log/gvpe.log 2>&1"

For systems using systemd, you can use a unit file ike this one:

   [Unit]
   Description=gvpe
   After=network.target
   Before=remote-fs.target

   [Service]
   ExecStart=/path/to/gvpe -D node
   KillMode=process
   Restart=always

   [Install]
   WantedBy=multi-user.target

=head1 SEE ALSO

gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
and for a description of the transports, protocol, and routing algorithm,
gvpe.protocol(7).

The GVPE mailing list, at L<http://lists.schmorp.de/>, or
C<gvpe@lists.schmorp.de>.

=head1 AUTHOR

Marc Lehmann <gvpe@schmorp.de>

=head1 COPYRIGHTS AND LICENSES

GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
COPYING that should be part of your distribution).

In some configurations it uses modified versions of the tinc vpn suite,
which is also available under the GENERAL PUBLIC LICENSE.

Revision:	1.12
Committed:	Wed Nov 2 06:54:13 2016 UTC (7 years, 11 months ago) by root
Branch:	MAIN
Changes since 1.11:	+48 -24 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	pcg	1.1	=head1 NAME
2
3			GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
4
5			=head1 DESCRIPTION
6
7			GVPE is a suite designed to provide a virtual private network for multiple
8	pcg	1.5	nodes over an untrusted network. This document first gives an introduction
9			to VPNs in general and then describes the specific implementation of GVPE.
10
11			=head2 WHAT IS A VPN?
12
13			VPN is an acronym, it stands for:
14	pcg	1.1
15	pcg	1.3	=over 4
16
17	pcg	1.9	=item Virtual
18	pcg	1.3
19	pcg	1.5	Virtual means that no physical network is created (of course), but a
20			network is I<emulated> by creating multiple tunnels between the member
21			nodes by encapsulating and sending data over another transport network.
22
23			Usually the emulated network is a normal IP or Ethernet, and the transport
24			network is the Internet. However, using a VPN system like GVPE to connect
25			nodes over other untrusted networks such as Wireless LAN is not uncommon.
26	pcg	1.1
27	pcg	1.9	=item Private
28	pcg	1.3
29			Private means that non-participating nodes cannot decode ("sniff)" nor
30	pcg	1.5	inject ("spoof") packets. This means that nodes can be connected over
31			untrusted networks such as the public Internet without fear of being
32			eavesdropped while at the same time being able to trust data sent by other
33			nodes.
34	pcg	1.1
35	pcg	1.5	In the case of GVPE, even participating nodes cannot sniff packets
36			send to other nodes or spoof packets as if sent from other nodes, so
37			communications between any two nodes is private to those two nodes.
38	pcg	1.1
39	pcg	1.9	=item Network
40	pcg	1.3
41			Network means that more than two parties can participate in the network,
42			so for instance it's possible to connect multiple branches of a company
43	pcg	1.8	into a single network. Many so-called "VPN" solutions only create
44	pcg	1.5	point-to-point tunnels, which in turn can be used to build larger
45			networks.
46
47	pcg	1.8	GVPE provides a true multi-point network in which any number of nodes (at
48	pcg	1.5	least a few dozen in practise, the theoretical limit is 4095 nodes) can
49			participate.
50	pcg	1.1
51	pcg	1.3	=back
52
53	pcg	1.5	=head2 GVPE DESIGN GOALS
54	pcg	1.1
55	root	1.10	=over 4
56	pcg	1.1
57			=item SIMPLE DESIGN
58
59			Cipher, HMAC algorithms and other key parameters must be selected
60			at compile time - this makes it possible to only link in algorithms
61			you actually need. It also makes the crypto part of the source very
62	pcg	1.5	transparent and easy to inspect, and last not least this makes it possible
63			to hardcode the layout of all packets into the binary. GVPE goes a step
64			further and internally reserves blocks of the same length for all packets,
65			which virtually removes all possibilities of buffer overflows, as there is
66			only a single type of buffer and it's always of fixed length.
67	pcg	1.1
68			=item EASY TO SETUP
69
70			A few lines of config (the config file is shared unmodified between all
71	root	1.12	hosts) and generating an RSA key-pair on each node suffices to make it
72			work.
73	pcg	1.1
74			=item MAC-BASED SECURITY
75
76			Since every host has it's own private key, other hosts cannot spoof
77			traffic from this host. That makes it possible to filter packet by MAC
78			address, e.g. to ensure that packets from a specific IP address come, in
79			fact, from a specific host that is associated with that IP and not from
80			another host.
81
82			=back
83
84			=head1 PROGRAMS
85
86	pcg	1.8	Gvpe comes with two programs: one daemon (C<gvpe>) and one control program
87	pcg	1.1	(C<gvpectrl>).
88
89			=over 4
90
91			=item gvpectrl
92
93	pcg	1.8	This program is used to generate the keys, check and give an overview of of the
94			configuration and to control the daemon (restarting etc.).
95	pcg	1.1
96			=item gvpe
97
98	pcg	1.8	This is the daemon used to establish and maintain connections to the other
99			network nodes. It should be run on the gateway of each VPN subnet.
100	pcg	1.1
101			=back
102
103			=head1 COMPILETIME CONFIGURATION
104
105			Please have a look at the C<gvpe.osdep(5)> manpage for platform-specific
106			information.
107
108	pcg	1.8	Gvpe hardcodes most encryption parameters. While this reduces flexibility,
109			it makes the program much simpler and helps making buffer overflows
110			impossible under most circumstances.
111
112	pcg	1.4	Here are a few recipes for compiling your gvpe, showing the extremes
113	pcg	1.8	(fast, small, insecure OR slow, large, more secure), between which you
114			should choose:
115	pcg	1.1
116			=head2 AS LOW PACKET OVERHEAD AS POSSIBLE
117
118			./configure --enable-hmac-length=4 --enable-rand-length=0
119
120	pcg	1.4	Minimize the header overhead of VPN packets (the above will result in
121			only 4 bytes of overhead over the raw ethernet frame). This is a insecure
122	root	1.11	configuration because a HMAC length of 4 makes collision attacks almost
123			trivial.
124	pcg	1.1
125			=head2 MINIMIZE CPU TIME REQUIRED
126
127			./configure --enable-cipher=bf --enable-digest=md4
128
129	pcg	1.4	Use the fastest cipher and digest algorithms currently available in
130	pcg	1.8	gvpe. MD4 has been broken and is quite insecure, though, so using another
131			digest algorithm is recommended.
132	pcg	1.1
133			=head2 MAXIMIZE SECURITY
134
135	root	1.11	./configure --enable-hmac-length=16 --enable-rand-length=12 --enable-digest=ripemd610
136	pcg	1.1
137			This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12
138			would also be pretty secure ;) and will additionally prefix each packet
139	root	1.11	with 12 bytes of random data.
140	pcg	1.1
141	pcg	1.8	In general, remember that AES-128 seems to be as secure but faster than
142	pcg	1.1	AES-192 or AES-256, more randomness helps against sniffing and a longer
143	pcg	1.8	HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
144			are consecutively better, and Blowfish is a fast cipher (and also quite
145			secure).
146	pcg	1.1
147			=head1 HOW TO SET UP A SIMPLE VPN
148
149			In this section I will describe how to get a simple VPN consisting of
150			three hosts up and running.
151
152			=head2 STEP 1: configuration
153
154	pcg	1.8	First you have to create a daemon configuration file and put it into the
155	pcg	1.1	configuration directory. This is usually C</etc/gvpe>, depending on how you
156	pcg	1.8	configured gvpe, and can be overwritten using the C<-c> command line switch.
157	pcg	1.1
158			Put the following lines into C</etc/gvpe/gvpe.conf>:
159
160			udp-port = 50000 # the external port to listen on (configure your firewall)
161			mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
162			ifname = vpn0 # the local network device name
163
164			node = first # just a nickname
165			hostname = first.example.net # the DNS name or IP address of the host
166
167			node = second
168			hostname = 133.55.82.9
169
170			node = third
171			hostname = third.example.net
172
173	pcg	1.8	The only other file necessary is the C<if-up> script that initializes the
174			virtual ethernet interface on the local host. Put the following lines into
175			C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):
176	pcg	1.1
177			#!/bin/sh
178			ip link set $IFNAME address $MAC mtu $MTU up
179			[ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
180			[ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
181			[ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
182			ip route add 10.0.0.0/16 dev $IFNAME
183
184			This script will give each node a different IP address in the C<10.0/16>
185	pcg	1.8	network. The internal network (if gvpe runs on a router) should then be
186	pcg	1.1	set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>,
187			C<10.0.2.0/24> on node C<second>, and so on.
188
189			By enabling routing on the gateway host that runs C<gvpe> all nodes will
190	pcg	1.8	be able to reach the other nodes. You can, of course, also use proxy ARP
191			or other means of pseudo-bridging, or (best) full routing - the choice is
192			yours.
193	pcg	1.1
194	root	1.12	=head2 STEP 2: create the RSA key pair for each node
195	pcg	1.1
196	root	1.12	Next you have to generate the RSA keys for the nodes. While you can set
197			up GVPE so you can generate all keys on a single host and centrally
198			distribute all keys, it is safer to generate the key for each node on the
199			node, so that the secret/private key does not have to be copied over the
200			network.
201	pcg	1.1
202	root	1.12	To do so, run the following command to generate a key pair:
203	pcg	1.1
204	root	1.12	gvpectrl -c /etc/gvpe -g nodekey
205	pcg	1.1
206	root	1.12	This will create two files, F<nodekey> and F<nodekey.privkey>. The former
207			should be copied to F<< /etc/gvpe/pubkey/I<nodename> >> on the host where
208			your config file is (you will have to create the F<pubkey> directory
209			first):
210
211			scp nodekey confighost:/etc/gvpe/pubkey/nodename
212	pcg	1.1
213	root	1.12	The private key F<nodekey.privkey> should be moved to F</etc/gvpe/hostkey>:
214	pcg	1.8
215	root	1.12	mkdir -p /etc/gvpe
216			mv nodekey.privkey /etc/gvpe/hostkey
217	pcg	1.1
218	root	1.12	=head2 STEP 3: distribute the config files to all nodes
219	pcg	1.1
220	root	1.12	Now distribute the config files and public keys to the other nodes.
221	pcg	1.1
222	root	1.12	The example uses rsync-over-ssh to copy the config file and all the public
223			keys:
224	pcg	1.1
225	root	1.12	rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkey
226			rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkey
227			rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkey
228	pcg	1.1
229	root	1.12	You should now check the configuration by issuing the command C<gvpectrl
230			-c /etc/gvpe -s> on each node and verify it's output.
231	pcg	1.1
232			=head2 STEP 4: starting gvpe
233
234			You should then start gvpe on each node by issuing a command like:
235
236	pcg	1.8	gvpe -D -l info first # first is the nodename
237	pcg	1.1
238	pcg	1.8	This will make the gvpe daemon stay in foreground. You should then see
239	pcg	1.1	"connection established" messages. If you don't see them check your
240			firewall and routing (use tcpdump ;).
241
242			If this works you should check your networking setup by pinging various
243			endpoints.
244
245	pcg	1.8	To make gvpe run more permanently you can either run it as a daemon (by
246			starting it without the C<-D> switch), or, much better, from your inittab
247			or equivalent. I use a line like this on all my systems:
248	pcg	1.1
249			t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
250
251			=head2 STEP 5: enjoy
252
253			... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
254			will make it try to connect to all other nodes again. If you run it from
255			inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will
256			kill the daemon, start it again, making it read it's configuration files
257			again.
258
259	root	1.12	To run the GVPE daemon permanently, you can either add it to your SysV
260			F<inittab>, e.g.:
261
262			t1:2345:respawn:/bin/sh -c "exec nice -n-20 /path/to/gvpe -D node >/var/log/gvpe.log 2>&1"
263
264			For systems using systemd, you can use a unit file ike this one:
265
266			[Unit]
267			Description=gvpe
268			After=network.target
269			Before=remote-fs.target
270
271			[Service]
272			ExecStart=/path/to/gvpe -D node
273			KillMode=process
274			Restart=always
275
276			[Install]
277			WantedBy=multi-user.target
278
279	pcg	1.1	=head1 SEE ALSO
280
281	pcg	1.8	gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
282	pcg	1.6	and for a description of the transports, protocol, and routing algorithm,
283			gvpe.protocol(7).
284	pcg	1.1
285	pcg	1.8	The GVPE mailing list, at L<http://lists.schmorp.de/>, or
286	pcg	1.7	C<gvpe@lists.schmorp.de>.
287
288	pcg	1.1	=head1 AUTHOR
289
290	pcg	1.7	Marc Lehmann <gvpe@schmorp.de>
291	pcg	1.1
292			=head1 COPYRIGHTS AND LICENSES
293
294			GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
295			COPYING that should be part of your distribution).
296
297			In some configurations it uses modified versions of the tinc vpn suite,
298			which is also available under the GENERAL PUBLIC LICENSE.
299