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12 12
13VPN is an acronym, it stands for: 13VPN is an acronym, it stands for:
14 14
15=over 4 15=over 4
16 16
17=item X<Virtual> 17=item Virtual
18 18
19Virtual means that no physical network is created (of course), but a 19Virtual means that no physical network is created (of course), but a
20network is I<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. 21nodes by encapsulating and sending data over another transport network.
22 22
23Usually the emulated network is a normal IP or Ethernet, and the transport 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 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. 25nodes over other untrusted networks such as Wireless LAN is not uncommon.
26 26
27=item X<Private> 27=item Private
28 28
29Private means that non-participating nodes cannot decode ("sniff)" nor 29Private means that non-participating nodes cannot decode ("sniff)" nor
30inject ("spoof") packets. This means that nodes can be connected over 30inject ("spoof") packets. This means that nodes can be connected over
31untrusted networks such as the public Internet without fear of being 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 32eavesdropped while at the same time being able to trust data sent by other
… …
34 34
35In the case of GVPE, even participating nodes cannot sniff packets 35In the case of GVPE, even participating nodes cannot sniff packets
36send to other nodes or spoof packets as if sent from other nodes, so 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. 37communications between any two nodes is private to those two nodes.
38 38
39=item X<Network> 39=item Network
40 40
41Network means that more than two parties can participate in the network, 41Network means that more than two parties can participate in the network,
42so 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
43into a single network. Many so-called "vpn" solutions only create 43into a single network. Many so-called "VPN" solutions only create
44point-to-point tunnels, which in turn can be used to build larger 44point-to-point tunnels, which in turn can be used to build larger
45networks. 45networks.
46 46
47GVPE provides a true multi-point network in wich any number of nodes (at 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 48least a few dozen in practise, the theoretical limit is 4095 nodes) can
49participate. 49participate.
50 50
51=back 51=back
52 52
53=head2 GVPE DESIGN GOALS 53=head2 GVPE DESIGN GOALS
54 54
55=over 4 55=over 4
56 56
57=item SIMPLE DESIGN 57=item SIMPLE DESIGN
58 58
59Cipher, HMAC algorithms and other key parameters must be selected 59Cipher, HMAC algorithms and other key parameters must be selected
60at compile time - this makes it possible to only link in algorithms 60at compile time - this makes it possible to only link in algorithms
… …
66only a single type of buffer and it's always of fixed length. 66only a single type of buffer and it's always of fixed length.
67 67
68=item EASY TO SETUP 68=item EASY TO SETUP
69 69
70A 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
71hosts) and a single run of C<gvpectrl> to generate the keys suffices to 71hosts) and generating an RSA key-pair on each node suffices to make it
72make it work. 72work.
73 73
74=item MAC-BASED SECURITY 74=item MAC-BASED SECURITY
75 75
76Since every host has it's own private key, other hosts cannot spoof 76Since every host has it's own private key, other hosts cannot spoof
77traffic from this host. That makes it possible to filter packet by MAC 77traffic from this host. That makes it possible to filter packet by MAC
… …
81 81
82=back 82=back
83 83
84=head1 PROGRAMS 84=head1 PROGRAMS
85 85
86Vpe 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
87(C<gvpectrl>). 87(C<gvpectrl>).
88 88
89=over 4 89=over 4
90 90
91=item gvpectrl 91=item gvpectrl
92 92
93Is 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
94configuration and contorl the daemon (restarting etc.). 94configuration and to control the daemon (restarting etc.).
95 95
96=item gvpe 96=item gvpe
97 97
98Is the daemon used to establish and maintain connections to the other 98This is the daemon used to establish and maintain connections to the other
99network members. It should be run on the gateway machine. 99network nodes. It should be run on the gateway of each VPN subnet.
100 100
101=back 101=back
102 102
103=head1 COMPILETIME CONFIGURATION 103=head1 COMPILETIME CONFIGURATION
104 104
105Please 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
106information. 106information.
107 107
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
108Here are a few recipes for compiling your gvpe, showing the extremes 112Here are a few recipes for compiling your gvpe, showing the extremes
109(fast, small, insecure OR slow, large, more secure), between you should 113(fast, small, insecure OR slow, large, more secure), between which you
110choose: 114should choose:
111 115
112=head2 AS LOW PACKET OVERHEAD AS POSSIBLE 116=head2 AS LOW PACKET OVERHEAD AS POSSIBLE
113 117
114 ./configure --enable-hmac-length=4 --enable-rand-length=0 118 ./configure --enable-hmac-length=4 --enable-rand-length=0
115 119
116Minimize the header overhead of VPN packets (the above will result in 120Minimize the header overhead of VPN packets (the above will result in
117only 4 bytes of overhead over the raw ethernet frame). This is a insecure 121only 4 bytes of overhead over the raw ethernet frame). This is a insecure
118configuration because a HMAC length of 4 makes collision attacks based on 122configuration because a HMAC length of 4 makes collision attacks almost
119the birthday paradox easy, though. 123trivial.
120 124
121=head2 MINIMIZE CPU TIME REQUIRED 125=head2 MINIMIZE CPU TIME REQUIRED
122 126
123 ./configure --enable-cipher=bf --enable-digest=md4 127 ./configure --enable-cipher=bf --enable-digest=md4
124 128
125Use the fastest cipher and digest algorithms currently available in 129Use the fastest cipher and digest algorithms currently available in
126gvpe. MD4 has been broken and is quite insecure, though. 130gvpe. MD4 has been broken and is quite insecure, though, so using another
131digest algorithm is recommended.
127 132
128=head2 MAXIMIZE SECURITY 133=head2 MAXIMIZE SECURITY
129 134
130 ./configure --enable-hmac-length=16 --enable-rand-length=8 --enable-digest=sha1 135 ./configure --enable-hmac-length=16 --enable-rand-length=12 --enable-digest=ripemd610
131 136
132This 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
133would also be pretty secure ;) and will additionally prefix each packet 138would also be pretty secure ;) and will additionally prefix each packet
134with 8 bytes of random data. In the long run, people should move to 139with 12 bytes of random data.
135SHA-224 and beyond, but support in openssl is missing as of writing this
136document.
137 140
138In 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
139AES-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
140HMAC helps against spoofing. MD4 is a fast digest, SHA1 or RIPEMD160 are 143HMAC helps against spoofing. MD4 is a fast digest, SHA1, RIPEMD160, SHA256
141better, and Blowfish is a fast cipher (and also quite secure). 144are consecutively better, and Blowfish is a fast cipher (and also quite
145secure).
142 146
143=head1 HOW TO SET UP A SIMPLE VPN 147=head1 HOW TO SET UP A SIMPLE VPN
144 148
145In 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
146three hosts up and running. 150three hosts up and running.
147 151
148=head2 STEP 1: configuration 152=head2 STEP 1: configuration
149 153
150First 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
151configuration directory. This is usually C</etc/gvpe>, depending on how you 155configuration directory. This is usually C</etc/gvpe>, depending on how you
152configured gvpe, and can be overwritten using the C<-c> commandline switch. 156configured gvpe, and can be overwritten using the C<-c> command line switch.
153 157
154Put the following lines into C</etc/gvpe/gvpe.conf>: 158Put the following lines into C</etc/gvpe/gvpe.conf>:
155 159
156 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)
157 mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts 161 mtu = 1400 # minimum MTU of all outgoing interfaces on all hosts
… …
164 hostname = 133.55.82.9 168 hostname = 133.55.82.9
165 169
166 node = third 170 node = third
167 hostname = third.example.net 171 hostname = third.example.net
168 172
169The 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
170local ethernet interface. Put the following lines into C</etc/gvpe/if-up> 174virtual ethernet interface on the local host. Put the following lines into
171and 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>):
172 176
173 #!/bin/sh 177 #!/bin/sh
174 ip link set $IFNAME address $MAC mtu $MTU up 178 ip link set $IFNAME address $MAC mtu $MTU up
175 [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME 179 [ $NODENAME = first ] && ip addr add 10.0.1.1 dev $IFNAME
176 [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME 180 [ $NODENAME = second ] && ip addr add 10.0.2.1 dev $IFNAME
177 [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME 181 [ $NODENAME = third ] && ip addr add 10.0.3.1 dev $IFNAME
178 ip route add 10.0.0.0/16 dev $IFNAME 182 ip route add 10.0.0.0/16 dev $IFNAME
179 183
180This 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>
181network. 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
182set 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>,
183C<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.
184 188
185By 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
186be 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
187or 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
188routing - the choice is yours. 192yours.
189 193
190=head2 STEP 2: create the RSA key pairs for all hosts 194=head2 STEP 2: create the RSA key pair for each node
191 195
192Run the following command to generate all key pairs (that might take a 196Next you have to generate the RSA keys for the nodes. While you can set
193while): 197up GVPE so you can generate all keys on a single host and centrally
198distribute all keys, it is safer to generate the key for each node on the
199node, so that the secret/private key does not have to be copied over the
200network.
194 201
202To do so, run the following command to generate a key pair:
203
195 gvpectrl -c /etc/gvpe -g 204 gvpectrl -c /etc/gvpe -g nodekey
196 205
197This command will put the public keys into C<< 206This will create two files, F<nodekey> and F<nodekey.privkey>. The former
198/etc/gvpe/pubkeys/I<nodename> >> and the private keys into C<< 207should be copied to F<< /etc/gvpe/pubkey/I<nodename> >> on the host where
199/etc/gvpe/hostkeys/I<nodename> >>. 208your config file is (you will have to create the F<pubkey> directory
209first):
210
211 scp nodekey confighost:/etc/gvpe/pubkey/nodename
212
213The private key F<nodekey.privkey> should be moved to F</etc/gvpe/hostkey>:
214
215 mkdir -p /etc/gvpe
216 mv nodekey.privkey /etc/gvpe/hostkey
200 217
201=head2 STEP 3: distribute the config files to all nodes 218=head2 STEP 3: distribute the config files to all nodes
202 219
203Now distribute the config files to the other nodes. This should be done in two steps, since the 220Now distribute the config files and public keys to the other nodes.
204private keys should not be distributed. The example uses rsync-over-ssh
205 221
206First all the config files without the hostkeys should be distributed: 222The example uses rsync-over-ssh to copy the config file and all the public
223keys:
207 224
208 rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkeys 225 rsync -avzessh /etc/gvpe first.example.net:/etc/. --exclude hostkey
209 rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkeys 226 rsync -avzessh /etc/gvpe 133.55.82.9:/etc/. --exclude hostkey
210 rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkeys 227 rsync -avzessh /etc/gvpe third.example.net:/etc/. --exclude hostkey
211 228
212Then the hostkeys should be copied:
213
214 rsync -avzessh /etc/gvpe/hostkeys/first first.example.net:/etc/hostkey
215 rsync -avzessh /etc/gvpe/hostkeys/second 133.55.82.9:/etc/hostkey
216 rsync -avzessh /etc/gvpe/hostkeys/third third.example.net:/etc/hostkey
217
218You should now check the configration by issuing the command C<gvpectrl -c 229You should now check the configuration by issuing the command C<gvpectrl
219/etc/gvpe -s> on each node and verify it's output. 230-c /etc/gvpe -s> on each node and verify it's output.
220 231
221=head2 STEP 4: starting gvpe 232=head2 STEP 4: starting gvpe
222 233
223You should then start gvpe on each node by issuing a command like: 234You should then start gvpe on each node by issuing a command like:
224 235
225 gvpe -D -linfo first # first is the nodename 236 gvpe -D -l info first # first is the nodename
226 237
227This will make the gvpe stay in foreground. You should then see 238This will make the gvpe daemon stay in foreground. You should then see
228"connection established" messages. If you don't see them check your 239"connection established" messages. If you don't see them check your
229firewall and routing (use tcpdump ;). 240firewall and routing (use tcpdump ;).
230 241
231If this works you should check your networking setup by pinging various 242If this works you should check your networking setup by pinging various
232endpoints. 243endpoints.
233 244
234To make gvpe run more permanently you can either run it as a daemon 245To make gvpe run more permanently you can either run it as a daemon (by
235(by starting it without the C<-D> switch), or, much better, from your 246starting it without the C<-D> switch), or, much better, from your inittab
236inittab. I use a line like this on my systems: 247or equivalent. I use a line like this on all my systems:
237 248
238 t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1 249 t1:2345:respawn:/opt/gvpe/sbin/gvpe -D -L first >/dev/null 2>&1
239 250
240=head2 STEP 5: enjoy 251=head2 STEP 5: enjoy
241 252
242... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon 253... and play around. Sending a -HUP (C<gvpectrl -kHUP>) to the daemon
243will make it try to connect to all other nodes again. If you run it from 254will make it try to connect to all other nodes again. If you run it from
244inittab, as is recommended, C<gvpectrl -k> (or simply C<killall gvpe>) will 255inittab C<gvpectrl -k> (or simply C<killall gvpe>) will kill the daemon,
245kill the daemon, start it again, making it read it's configuration files 256start it again, making it read it's configuration files again.
246again. 257
258To run the GVPE daemon permanently from your SysV init, you can add it to
259your F<inittab>, e.g.:
260
261 t1:2345:respawn:/bin/sh -c "exec nice -n-20 /path/to/gvpe -D node >/var/log/gvpe.log 2>&1"
262
263For systems using systemd, you can use a unit file similar to this one:
264
265 [Unit]
266 Description=gvpe
267 After=network.target
268 Before=remote-fs.target
269
270 [Service]
271 ExecStart=/path/to/gvpe -D node
272 KillMode=process
273 Restart=always
274
275 [Install]
276 WantedBy=multi-user.target
247 277
248=head1 SEE ALSO 278=head1 SEE ALSO
249 279
250gvpe.osdep(5) for OS-depedendent information, gvpe.conf(5), gvpectrl(8), 280gvpe.osdep(5) for OS-dependent information, gvpe.conf(5), gvpectrl(8),
251and for a description of the transports, protocol, and routing algorithm, 281and for a description of the transports, protocol, and routing algorithm,
252gvpe.protocol(7). 282gvpe.protocol(7).
253 283
254The GVPE mailinglist, at L<http://lists.schmorp.de/>, or 284The GVPE mailing list, at L<http://lists.schmorp.de/>, or
255C<gvpe@lists.schmorp.de>. 285C<gvpe@lists.schmorp.de>.
256 286
257=head1 AUTHOR 287=head1 AUTHOR
258 288
259Marc Lehmann <gvpe@schmorp.de> 289Marc Lehmann <gvpe@schmorp.de>

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