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3GNU-VPE - Overview of the GNU Virtual Private Ethernet suite. 3GNU-VPE - Overview of the GNU Virtual Private Ethernet suite.
4 4
5=head1 DESCRIPTION 5=head1 DESCRIPTION
6 6
7GVPE is a suite designed to provide a virtual private network for multiple 7GVPE is a suite designed to provide a virtual private network for multiple
8nodes over an untrusted network. 8nodes over an untrusted network. This document first gives an introduction
9to VPNs in general and then describes the specific implementation of GVPE.
10
11=head2 WHAT IS A VPN?
12
13VPN is an acronym, it stands for:
9 14
10=over 4 15=over 4
11 16
12=item X<Virtual> 17=item Virtual
13 18
14Virtual means that no physical network is created (of course), but an 19Virtual means that no physical network is created (of course), but a
15ethernet is emulated by creating multiple tunnels between the member 20network is I<emulated> by creating multiple tunnels between the member
21nodes by encapsulating and sending data over another transport network.
22
23Usually the emulated network is a normal IP or Ethernet, and the transport
24network is the Internet. However, using a VPN system like GVPE to connect
25nodes over other untrusted networks such as Wireless LAN is not uncommon.
26
27=item Private
28
29Private means that non-participating nodes cannot decode ("sniff)" nor
30inject ("spoof") packets. This means that nodes can be connected over
31untrusted networks such as the public Internet without fear of being
32eavesdropped while at the same time being able to trust data sent by other
16nodes. 33nodes.
17 34
18=item X<Private>
19
20Private means that non-participating nodes cannot decode ("sniff)" nor
21inject ("spoof") packets.
22
23In the case of gvpe, even participating nodes cannot sniff packets send to 35In the case of GVPE, even participating nodes cannot sniff packets
24other nodes or spoof packets as if sent from other nodes. 36send to other nodes or spoof packets as if sent from other nodes, so
37communications between any two nodes is private to those two nodes.
25 38
26=item X<Network> 39=item Network
27 40
28Network means that more than two parties can participate in the network, 41Network means that more than two parties can participate in the network,
29so for instance it's possible to connect multiple branches of a company 42so for instance it's possible to connect multiple branches of a company
30into a single network. Many so-called "vpn" solutions only create 43into a single network. Many so-called "VPN" solutions only create
31point-to-point tunnels. 44point-to-point tunnels, which in turn can be used to build larger
45networks.
46
47GVPE provides a true multi-point network in which any number of nodes (at
48least a few dozen in practise, the theoretical limit is 4095 nodes) can
49participate.
32 50
33=back 51=back
34 52
35=head2 DESIGN GOALS 53=head2 GVPE DESIGN GOALS
36 54
37=over 4 55=over 4
38 56
39=item SIMPLE DESIGN 57=item SIMPLE DESIGN
40 58
41Cipher, HMAC algorithms and other key parameters must be selected 59Cipher, HMAC algorithms and other key parameters must be selected
42at compile time - this makes it possible to only link in algorithms 60at compile time - this makes it possible to only link in algorithms
43you actually need. It also makes the crypto part of the source very 61you actually need. It also makes the crypto part of the source very
44transparent and easy to inspect. 62transparent and easy to inspect, and last not least this makes it possible
63to hardcode the layout of all packets into the binary. GVPE goes a step
64further and internally reserves blocks of the same length for all packets,
65which virtually removes all possibilities of buffer overflows, as there is
66only a single type of buffer and it's always of fixed length.
45 67
46=item EASY TO SETUP 68=item EASY TO SETUP
47 69
48A few lines of config (the config file is shared unmodified between all 70A few lines of config (the config file is shared unmodified between all
49hosts) and a single run of C<gvpectrl> to generate the keys suffices to 71hosts) and a single run of C<gvpectrl> to generate the keys suffices to
… …
59 81
60=back 82=back
61 83
62=head1 PROGRAMS 84=head1 PROGRAMS
63 85
64Vpe comes with two programs: one daemon (C<gvpe>) and one control program 86Gvpe comes with two programs: one daemon (C<gvpe>) and one control program
65(C<gvpectrl>). 87(C<gvpectrl>).
66 88
67=over 4 89=over 4
68 90
69=item gvpectrl 91=item gvpectrl
70 92
71Is used to generate the keys, check and give an overview of of the 93This program is used to generate the keys, check and give an overview of of the
72configuration and contorl the daemon (restarting etc.). 94configuration and to control the daemon (restarting etc.).
73 95
74=item gvpe 96=item gvpe
75 97
76Is the daemon used to establish and maintain connections to the other 98This is the daemon used to establish and maintain connections to the other
77network members. It should be run on the gateway machine. 99network nodes. It should be run on the gateway of each VPN subnet.
78 100
79=back 101=back
80 102
81=head1 COMPILETIME CONFIGURATION 103=head1 COMPILETIME CONFIGURATION
82 104
83Please have a look at the C<gvpe.osdep(5)> manpage for platform-specific 105Please have a look at the C<gvpe.osdep(5)> manpage for platform-specific
84information. 106information.
85 107
108Gvpe hardcodes most encryption parameters. While this reduces flexibility,
109it makes the program much simpler and helps making buffer overflows
110impossible under most circumstances.
111
86Here are a few recipes for compiling your gvpe: 112Here are a few recipes for compiling your gvpe, showing the extremes
113(fast, small, insecure OR slow, large, more secure), between which you
114should choose:
87 115
88=head2 AS LOW PACKET OVERHEAD AS POSSIBLE 116=head2 AS LOW PACKET OVERHEAD AS POSSIBLE
89 117
90 ./configure --enable-hmac-length=4 --enable-rand-length=0 118 ./configure --enable-hmac-length=4 --enable-rand-length=0
91 119
92Minimize the header overhead of VPN packets (the above will result in only 120Minimize the header overhead of VPN packets (the above will result in
934 bytes of overhead over the raw ethernet frame). 121only 4 bytes of overhead over the raw ethernet frame). This is a insecure
122configuration because a HMAC length of 4 makes collision attacks based on
123the birthday paradox pretty easy.
94 124
95=head2 MINIMIZE CPU TIME REQUIRED 125=head2 MINIMIZE CPU TIME REQUIRED
96 126
97 ./configure --enable-cipher=bf --enable-digest=md4 127 ./configure --enable-cipher=bf --enable-digest=md4
98 128
99Use the fastest cipher and digest algorithms currently available in gvpe. 129Use the fastest cipher and digest algorithms currently available in
130gvpe. MD4 has been broken and is quite insecure, though, so using another
131digest algorithm is recommended.
100 132
101=head2 MAXIMIZE SECURITY 133=head2 MAXIMIZE SECURITY
102 134
103 ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1 135 ./configure --enable-hmac-length=16 --enable-rand-length=16 --enable-digest=sha384
104 136
105This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12 137This uses a 16 byte HMAC checksum to authenticate packets (I guess 8-12
106would also be pretty secure ;) and will additionally prefix each packet 138would also be pretty secure ;) and will additionally prefix each packet
107with 8 bytes of random data. In the long run, people should move to 139with 16 bytes of random data.
108SHA-224 and beyond, but support in openssl is missing as of writing this
109document.
110 140
111In general, remember that AES-128 seems to be more secure and faster than 141In general, remember that AES-128 seems to be as secure but faster than
112AES-192 or AES-256, more randomness helps against sniffing and a longer 142AES-192 or AES-256, more randomness helps against sniffing and a longer
113HMAC helps against spoofing. MD4 is a fast digest, SHA1 or RIPEMD160 are 143HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
114better, and Blowfish is a fast cipher (and also quite secure). 144are consecutively better, and Blowfish is a fast cipher (and also quite
145secure).
115 146
116=head1 HOW TO SET UP A SIMPLE VPN 147=head1 HOW TO SET UP A SIMPLE VPN
117 148
118In this section I will describe how to get a simple VPN consisting of 149In this section I will describe how to get a simple VPN consisting of
119three hosts up and running. 150three hosts up and running.
120 151
121=head2 STEP 1: configuration 152=head2 STEP 1: configuration
122 153
123First you have to create a daemon configuation file and put it into the 154First you have to create a daemon configuration file and put it into the
124configuration directory. This is usually C</etc/gvpe>, depending on how you 155configuration directory. This is usually C</etc/gvpe>, depending on how you
125configured gvpe, and can be overwritten using the C<-c> commandline switch. 156configured gvpe, and can be overwritten using the C<-c> command line switch.
126 157
127Put the following lines into C</etc/gvpe/gvpe.conf>: 158Put the following lines into C</etc/gvpe/gvpe.conf>:
128 159
129 udp-port = 50000 # the external port to listen on (configure your firewall) 160 udp-port = 50000 # the external port to listen on (configure your firewall)
130 mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts 161 mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
… …
137 hostname = 133.55.82.9 168 hostname = 133.55.82.9
138 169
139 node = third 170 node = third
140 hostname = third.example.net 171 hostname = third.example.net
141 172
142The only other file neccessary if the C<if-up> script that initializes the 173The only other file necessary is the C<if-up> script that initializes the
143local ethernet interface. Put the following lines into C</etc/gvpe/if-up> 174virtual ethernet interface on the local host. Put the following lines into
144and make it execute (C<chmod 755 /etc/gvpe/if-up>): 175C</etc/gvpe/if-up> and make it executable (C<chmod 755 /etc/gvpe/if-up>):
145 176
146 #!/bin/sh 177 #!/bin/sh
147 ip link set $IFNAME address $MAC mtu $MTU up 178 ip link set $IFNAME address $MAC mtu $MTU up
148 [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME 179 [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
149 [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME 180 [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
150 [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME 181 [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
151 ip route add 10.0.0.0/16 dev $IFNAME 182 ip route add 10.0.0.0/16 dev $IFNAME
152 183
153This script will give each node a different IP address in the C<10.0/16> 184This script will give each node a different IP address in the C<10.0/16>
154network. The internal network (e.g. the C<eth0> interface) should then be 185network. The internal network (if gvpe runs on a router) should then be
155set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>, 186set to a subset of that network, e.g. C<10.0.1.0/24> on node C<first>,
156C<10.0.2.0/24> on node C<second>, and so on. 187C<10.0.2.0/24> on node C<second>, and so on.
157 188
158By enabling routing on the gateway host that runs C<gvpe> all nodes will 189By enabling routing on the gateway host that runs C<gvpe> all nodes will
159be able to reach the other nodes. You can, of course, also use proxy arp 190be able to reach the other nodes. You can, of course, also use proxy ARP
160or other means of pseudo-bridging (or even real briding), or (best) full 191or other means of pseudo-bridging, or (best) full routing - the choice is
161routing - the choice is yours. 192yours.
162 193
163=head2 STEP 2: create the RSA key pairs for all hosts 194=head2 STEP 2: create the RSA key pairs for all hosts
164 195
165Run the following command to generate all key pairs (that might take a 196Run the following command to generate all key pairs for all nodes (that
166while): 197might take a while):
167 198
168 gvpectrl -c /etc/gvpe -g 199 gvpectrl -c /etc/gvpe -g
169 200
170This command will put the public keys into C<< 201This command will put the public keys into C<<
171/etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<< 202/etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<<
172/etc/gvpe/hostkeys/I<nodename> >>. 203/etc/gvpe/hostkeys/I<nodename> >>.
173 204
174=head2 STEP 3: distribute the config files to all nodes 205=head2 STEP 3: distribute the config files to all nodes
175 206
176Now distribute the config files to the other nodes. This should be done in two steps, since the 207Now distribute the config files and private keys to the other nodes. This
177private keys should not be distributed. The example uses rsync-over-ssh 208should be done in two steps, since only the private keys meant for a node
209should be distributed (so each node has only it's own private key).
210
211The example uses rsync-over-ssh
178 212
179First all the config files without the hostkeys should be distributed: 213First all the config files without the hostkeys should be distributed:
180 214
181 rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys 215 rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys
182 rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys 216 rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys
… …
186 220
187 rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey 221 rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
188 rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey 222 rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
189 rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey 223 rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
190 224
191You should now check the configration by issuing the command C<gvpectrl -c 225You should now check the configuration by issuing the command C<gvpectrl -c
192/etc/gvpe -s> on each node and verify it's output. 226/etc/gvpe -s> on each node and verify it's output.
193 227
194=head2 STEP 4: starting gvpe 228=head2 STEP 4: starting gvpe
195 229
196You should then start gvpe on each node by issuing a command like: 230You should then start gvpe on each node by issuing a command like:
197 231
198 gvpe -D -linfo first # first is the nodename 232 gvpe -D -l info first # first is the nodename
199 233
200This will make the gvpe stay in foreground. You should then see 234This will make the gvpe daemon stay in foreground. You should then see
201"connection established" messages. If you don't see them check your 235"connection established" messages. If you don't see them check your
202firewall and routing (use tcpdump ;). 236firewall and routing (use tcpdump ;).
203 237
204If this works you should check your networking setup by pinging various 238If this works you should check your networking setup by pinging various
205endpoints. 239endpoints.
206 240
207To make gvpe run more permanently you can either run it as a daemon 241To make gvpe run more permanently you can either run it as a daemon (by
208(by starting it without the C<-D> switch), or, much better, from your 242starting it without the C<-D> switch), or, much better, from your inittab
209inittab. I use a line like this on my systems: 243or equivalent. I use a line like this on all my systems:
210 244
211 t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1 245 t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
212 246
213=head2 STEP 5: enjoy 247=head2 STEP 5: enjoy
214 248
… …
218kill the daemon, start it again, making it read it's configuration files 252kill the daemon, start it again, making it read it's configuration files
219again. 253again.
220 254
221=head1 SEE ALSO 255=head1 SEE ALSO
222 256
223gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8), and 257gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
224for a description of the protocol and routing algorithms, gvpe.protocol(7). 258and for a description of the transports, protocol, and routing algorithm,
259gvpe.protocol(7).
260
261The GVPE mailing list, at L<http://lists.schmorp.de/>, or
262C<gvpe@lists.schmorp.de>.
225 263
226=head1 AUTHOR 264=head1 AUTHOR
227 265
228Marc Lehmann <gvpe@plan9.de> 266Marc Lehmann <gvpe@schmorp.de>
229 267
230=head1 COPYRIGHTS AND LICENSES 268=head1 COPYRIGHTS AND LICENSES
231 269
232GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file 270GVPE itself is distributed under the GENERAL PUBLIC LICENSE (see the file
233COPYING that should be part of your distribution). 271COPYING that should be part of your distribution).

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