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 a single run of C<gvpectrl> to generate the keys 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 based on
the birthday paradox pretty easy.

=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=8 --enable-digest=sha1

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 8 bytes of random data. In the long run, people should move to
SHA-256 and beyond).

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 pairs for all hosts

Run the following command to generate all key pairs for all nodes (that
might take a while):

   gvpectrl -c /etc/gvpe -g

This command will put the public keys into C<<
/etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<<
/etc/gvpe/hostkeys/I<nodename> >>.

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

Now distribute the config files and private keys to the other nodes. This
should be done in two steps, since only the private keys meant for a node
should be distributed (so each node has only it's own private key).

The example uses rsync-over-ssh

First all the config files without the hostkeys should be distributed:

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

Then the hostkeys should be copied:

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

=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:	1.9
Committed:	Mon Sep 1 06:06:11 2008 UTC (15 years, 8 months ago) by pcg
Branch:	MAIN
CVS Tags:	rel-2_21, rel-2_22
Changes since 1.8:	+3 -3 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			=over 4
56
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			hosts) and a single run of C<gvpectrl> to generate the keys suffices to
72			make it work.
73
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			configuration because a HMAC length of 4 makes collision attacks based on
123	pcg	1.8	the birthday paradox pretty easy.
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			./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1
136
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	pcg	1.2	with 8 bytes of random data. In the long run, people should move to
140	pcg	1.8	SHA-256 and beyond).
141	pcg	1.1
142	pcg	1.8	In general, remember that AES-128 seems to be as secure but faster than
143	pcg	1.1	AES-192 or AES-256, more randomness helps against sniffing and a longer
144	pcg	1.8	HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
145			are consecutively better, and Blowfish is a fast cipher (and also quite
146			secure).
147	pcg	1.1
148			=head1 HOW TO SET UP A SIMPLE VPN
149
150			In this section I will describe how to get a simple VPN consisting of
151			three hosts up and running.
152
153			=head2 STEP 1: configuration
154
155	pcg	1.8	First you have to create a daemon configuration file and put it into the
156	pcg	1.1	configuration directory. This is usually C</etc/gvpe>, depending on how you
157	pcg	1.8	configured gvpe, and can be overwritten using the C<-c> command line switch.
158	pcg	1.1
159			Put the following lines into C</etc/gvpe/gvpe.conf>:
160
161			udp-port = 50000 # the external port to listen on (configure your firewall)
162			mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
163			ifname = vpn0 # the local network device name
164
165			node = first # just a nickname
166			hostname = first.example.net # the DNS name or IP address of the host
167
168			node = second
169			hostname = 133.55.82.9
170
171			node = third
172			hostname = third.example.net
173
174	pcg	1.8	The only other file necessary is the C<if-up> script that initializes the
175			virtual ethernet interface on the local host. Put the following lines into
176			C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):
177	pcg	1.1
178			#!/bin/sh
179			ip link set $IFNAME address $MAC mtu $MTU up
180			[ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
181			[ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
182			[ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
183			ip route add 10.0.0.0/16 dev $IFNAME
184
185			This script will give each node a different IP address in the C<10.0/16>
186	pcg	1.8	network. The internal network (if gvpe runs on a router) should then be
187	pcg	1.1	set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>,
188			C<10.0.2.0/24> on node C<second>, and so on.
189
190			By enabling routing on the gateway host that runs C<gvpe> all nodes will
191	pcg	1.8	be able to reach the other nodes. You can, of course, also use proxy ARP
192			or other means of pseudo-bridging, or (best) full routing - the choice is
193			yours.
194	pcg	1.1
195			=head2 STEP 2: create the RSA key pairs for all hosts
196
197	pcg	1.8	Run the following command to generate all key pairs for all nodes (that
198			might take a while):
199	pcg	1.1
200			gvpectrl -c /etc/gvpe -g
201
202			This command will put the public keys into C<<
203			/etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<<
204			/etc/gvpe/hostkeys/I<nodename> >>.
205
206			=head2 STEP 3: distribute the config files to all nodes
207
208	pcg	1.8	Now distribute the config files and private keys to the other nodes. This
209			should be done in two steps, since only the private keys meant for a node
210			should be distributed (so each node has only it's own private key).
211
212			The example uses rsync-over-ssh
213	pcg	1.1
214			First all the config files without the hostkeys should be distributed:
215
216			rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
217			rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
218			rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys
219
220			Then the hostkeys should be copied:
221
222			rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
223			rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
224			rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
225
226	pcg	1.8	You should now check the configuration by issuing the command C<gvpectrl -c
227	pcg	1.1	/etc/gvpe -s> on each node and verify it's output.
228
229			=head2 STEP 4: starting gvpe
230
231			You should then start gvpe on each node by issuing a command like:
232
233	pcg	1.8	gvpe -D -l info first # first is the nodename
234	pcg	1.1
235	pcg	1.8	This will make the gvpe daemon stay in foreground. You should then see
236	pcg	1.1	"connection established" messages. If you don't see them check your
237			firewall and routing (use tcpdump ;).
238
239			If this works you should check your networking setup by pinging various
240			endpoints.
241
242	pcg	1.8	To make gvpe run more permanently you can either run it as a daemon (by
243			starting it without the C<-D> switch), or, much better, from your inittab
244			or equivalent. I use a line like this on all my systems:
245	pcg	1.1
246			t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
247
248			=head2 STEP 5: enjoy
249
250			... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
251			will make it try to connect to all other nodes again. If you run it from
252			inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will
253			kill the daemon, start it again, making it read it's configuration files
254			again.
255
256			=head1 SEE ALSO
257
258	pcg	1.8	gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
259	pcg	1.6	and for a description of the transports, protocol, and routing algorithm,
260			gvpe.protocol(7).
261	pcg	1.1
262	pcg	1.8	The GVPE mailing list, at L<http://lists.schmorp.de/>, or
263	pcg	1.7	C<gvpe@lists.schmorp.de>.
264
265	pcg	1.1	=head1 AUTHOR
266
267	pcg	1.7	Marc Lehmann <gvpe@schmorp.de>
268	pcg	1.1
269			=head1 COPYRIGHTS AND LICENSES
270
271			GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
272			COPYING that should be part of your distribution).
273
274			In some configurations it uses modified versions of the tinc vpn suite,
275			which is also available under the GENERAL PUBLIC LICENSE.
276