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| 46 | . ds PI \(*p |
38 | . ds PI \(*p |
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39 | . ds L" `` |
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| 129 | .\" ======================================================================== |
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| 131 | .IX Title "GVPE.PROTOCOL 7" |
126 | .IX Title "GVPE.PROTOCOL 7" |
| 132 | .TH GVPE.PROTOCOL 7 "2008-08-10" "2.2" "GNU Virtual Private Ethernet" |
127 | .TH GVPE.PROTOCOL 7 "2013-07-19" "2.25" "GNU Virtual Private Ethernet" |
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128 | .\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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130 | .if n .ad l |
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131 | .nh |
| 133 | .SH "The GNU-VPE Protocols" |
132 | .SH "The GNU-VPE Protocols" |
| 134 | .IX Header "The GNU-VPE Protocols" |
133 | .IX Header "The GNU-VPE Protocols" |
| 135 | .SH "Overview" |
134 | .SH "Overview" |
| 136 | .IX Header "Overview" |
135 | .IX Header "Overview" |
| 137 | \&\s-1GVPE\s0 can make use of a number of protocols. One of them is the \s-1GNU\s0 \s-1VPE\s0 |
136 | \&\s-1GVPE\s0 can make use of a number of protocols. One of them is the \s-1GNU\s0 \s-1VPE\s0 |
| … | |
… | |
| 148 | reliability, and robustness. |
147 | reliability, and robustness. |
| 149 | .PP |
148 | .PP |
| 150 | The following sections describe each transport protocol in more |
149 | The following sections describe each transport protocol in more |
| 151 | detail. They are sorted by overhead/efficiency, the most efficient |
150 | detail. They are sorted by overhead/efficiency, the most efficient |
| 152 | transport is listed first: |
151 | transport is listed first: |
| 153 | .Sh "\s-1RAW\s0 \s-1IP\s0" |
152 | .SS "\s-1RAW\s0 \s-1IP\s0" |
| 154 | .IX Subsection "RAW IP" |
153 | .IX Subsection "RAW IP" |
| 155 | This protocol is the best choice, performance\-wise, as the minimum |
154 | This protocol is the best choice, performance-wise, as the minimum |
| 156 | overhead per packet is only 38 bytes. |
155 | overhead per packet is only 38 bytes. |
| 157 | .PP |
156 | .PP |
| 158 | It works by sending the \s-1VPN\s0 payload using raw ip frames (using the |
157 | It works by sending the \s-1VPN\s0 payload using raw \s-1IP\s0 frames (using the |
| 159 | protocol set by \f(CW\*(C`ip\-proto\*(C'\fR). |
158 | protocol set by \f(CW\*(C`ip\-proto\*(C'\fR). |
| 160 | .PP |
159 | .PP |
| 161 | Using raw ip frames has the drawback that many firewalls block \*(L"unknown\*(R" |
160 | Using raw \s-1IP\s0 frames has the drawback that many firewalls block \*(L"unknown\*(R" |
| 162 | protocols, so this transport only works if you have full \s-1IP\s0 connectivity |
161 | protocols, so this transport only works if you have full \s-1IP\s0 connectivity |
| 163 | between nodes. |
162 | between nodes. |
| 164 | .Sh "\s-1ICMP\s0" |
163 | .SS "\s-1ICMP\s0" |
| 165 | .IX Subsection "ICMP" |
164 | .IX Subsection "ICMP" |
| 166 | This protocol offers very low overhead (minimum 42 bytes), and can |
165 | This protocol offers very low overhead (minimum 42 bytes), and can |
| 167 | sometimes tunnel through firewalls when other protocols can not. |
166 | sometimes tunnel through firewalls when other protocols can not. |
| 168 | .PP |
167 | .PP |
| 169 | It works by prepending an \s-1ICMP\s0 header with type \f(CW\*(C`icmp\-type\*(C'\fR and a code |
168 | It works by prepending an \s-1ICMP\s0 header with type \f(CW\*(C`icmp\-type\*(C'\fR and a code |
| 170 | of \f(CW255\fR. The default \f(CW\*(C`icmp\-type\*(C'\fR is \f(CW\*(C`echo\-reply\*(C'\fR, so the resulting |
169 | of \f(CW255\fR. The default \f(CW\*(C`icmp\-type\*(C'\fR is \f(CW\*(C`echo\-reply\*(C'\fR, so the resulting |
| 171 | packets look like echo replies, which looks rather strange to network |
170 | packets look like echo replies, which looks rather strange to network |
| 172 | admins. |
171 | administrators. |
| 173 | .PP |
172 | .PP |
| 174 | This transport should only be used if other transports (i.e. raw ip) are |
173 | This transport should only be used if other transports (i.e. raw \s-1IP\s0) are |
| 175 | not available or undesirable (due to their overhead). |
174 | not available or undesirable (due to their overhead). |
| 176 | .Sh "\s-1UDP\s0" |
175 | .SS "\s-1UDP\s0" |
| 177 | .IX Subsection "UDP" |
176 | .IX Subsection "UDP" |
| 178 | This is a good general choice for the transport protocol as \s-1UDP\s0 packets |
177 | This is a good general choice for the transport protocol as \s-1UDP\s0 packets |
| 179 | tunnel well through most firewalls and routers, and the overhead per |
178 | tunnel well through most firewalls and routers, and the overhead per |
| 180 | packet is moderate (minimum 58 bytes). |
179 | packet is moderate (minimum 58 bytes). |
| 181 | .PP |
180 | .PP |
| 182 | It should be used if \s-1RAW\s0 \s-1IP\s0 is not available. |
181 | It should be used if \s-1RAW\s0 \s-1IP\s0 is not available. |
| 183 | .Sh "\s-1TCP\s0" |
182 | .SS "\s-1TCP\s0" |
| 184 | .IX Subsection "TCP" |
183 | .IX Subsection "TCP" |
| 185 | This protocol is a very bad choice, as it not only has high overhead (more |
184 | This protocol is a very bad choice, as it not only has high overhead (more |
| 186 | than 60 bytes), but the transport also retries on it's own, which leads |
185 | than 60 bytes), but the transport also retries on it's own, which leads |
| 187 | to congestion when the link has moderate packet loss (as both the \s-1TCP\s0 |
186 | to congestion when the link has moderate packet loss (as both the \s-1TCP\s0 |
| 188 | transport and the tunneled traffic will retry, increasing congestion more |
187 | transport and the tunneled traffic will retry, increasing congestion more |
| … | |
… | |
| 197 | It is an abuse of the usage a proxy was designed for, so make sure you are |
196 | It is an abuse of the usage a proxy was designed for, so make sure you are |
| 198 | allowed to use it for \s-1GVPE\s0. |
197 | allowed to use it for \s-1GVPE\s0. |
| 199 | .PP |
198 | .PP |
| 200 | This protocol also has server and client sides. If the \f(CW\*(C`tcp\-port\*(C'\fR is |
199 | This protocol also has server and client sides. If the \f(CW\*(C`tcp\-port\*(C'\fR is |
| 201 | set to zero, other nodes cannot connect to this node directly. If the |
200 | set to zero, other nodes cannot connect to this node directly. If the |
| 202 | \&\f(CW\*(C`tcp\-port\*(C'\fR is non\-zero, the node can act both as a client as well as a |
201 | \&\f(CW\*(C`tcp\-port\*(C'\fR is non-zero, the node can act both as a client as well as a |
| 203 | server. |
202 | server. |
| 204 | .Sh "\s-1DNS\s0" |
203 | .SS "\s-1DNS\s0" |
| 205 | .IX Subsection "DNS" |
204 | .IX Subsection "DNS" |
| 206 | \&\fB\s-1WARNING:\s0\fR Parsing and generating \s-1DNS\s0 packets is rather tricky. The code |
205 | \&\fB\s-1WARNING:\s0\fR Parsing and generating \s-1DNS\s0 packets is rather tricky. The code |
| 207 | almost certainly contains buffer overflows and other, likely exploitable, |
206 | almost certainly contains buffer overflows and other, likely exploitable, |
| 208 | bugs. You have been warned. |
207 | bugs. You have been warned. |
| 209 | .PP |
208 | .PP |
| … | |
… | |
| 215 | traffic even if it doesn't need to transport packets. |
214 | traffic even if it doesn't need to transport packets. |
| 216 | .PP |
215 | .PP |
| 217 | In addition, the same problems as the \s-1TCP\s0 transport also plague this |
216 | In addition, the same problems as the \s-1TCP\s0 transport also plague this |
| 218 | protocol. |
217 | protocol. |
| 219 | .PP |
218 | .PP |
| 220 | It's only use is to tunnel through firewalls that do not allow direct |
219 | Its only use is to tunnel through firewalls that do not allow direct |
| 221 | internet access. Similar to using a \s-1HTTP\s0 proxy (as the \s-1TCP\s0 transport |
220 | internet access. Similar to using a \s-1HTTP\s0 proxy (as the \s-1TCP\s0 transport |
| 222 | does), it uses a local \s-1DNS\s0 server/forwarder (given by the \f(CW\*(C`dns\-forw\-host\*(C'\fR |
221 | does), it uses a local \s-1DNS\s0 server/forwarder (given by the \f(CW\*(C`dns\-forw\-host\*(C'\fR |
| 223 | configuration value) as a proxy to send and receive data as a client, |
222 | configuration value) as a proxy to send and receive data as a client, |
| 224 | and an \f(CW\*(C`NS\*(C'\fR record pointing to the \s-1GVPE\s0 server (as given by the |
223 | and an \f(CW\*(C`NS\*(C'\fR record pointing to the \s-1GVPE\s0 server (as given by the |
| 225 | \&\f(CW\*(C`dns\-hostname\*(C'\fR directive). |
224 | \&\f(CW\*(C`dns\-hostname\*(C'\fR directive). |
| 226 | .PP |
225 | .PP |
| 227 | The only good side of this protocol is that it can tunnel through most |
226 | The only good side of this protocol is that it can tunnel through most |
| 228 | firewalls mostly undetected, iff the local \s-1DNS\s0 server/forwarder is sane |
227 | firewalls mostly undetected, iff the local \s-1DNS\s0 server/forwarder is sane |
| 229 | (which is true for most routers, \s-1WLAN\s0 gateways and nameservers). |
228 | (which is true for most routers, wireless \s-1LAN\s0 gateways and nameservers). |
| 230 | .PP |
229 | .PP |
| 231 | Finetuning needs to be done by editing \f(CW\*(C`src/vpn_dns.C\*(C'\fR directly. |
230 | Fine-tuning needs to be done by editing \f(CW\*(C`src/vpn_dns.C\*(C'\fR directly. |
| 232 | .SH "PART 2: The GNU VPE protocol" |
231 | .SH "PART 2: The GNU VPE protocol" |
| 233 | .IX Header "PART 2: The GNU VPE protocol" |
232 | .IX Header "PART 2: The GNU VPE protocol" |
| 234 | This section, unfortunately, is not yet finished, although the protocol |
233 | This section, unfortunately, is not yet finished, although the protocol |
| 235 | is stable (until bugs in the cryptography are found, which will likely |
234 | is stable (until bugs in the cryptography are found, which will likely |
| 236 | completely change the following description). Nevertheless, it should give |
235 | completely change the following description). Nevertheless, it should give |
| 237 | you some overview over the protocol. |
236 | you some overview over the protocol. |
| 238 | .Sh "Anatomy of a \s-1VPN\s0 packet" |
237 | .SS "Anatomy of a \s-1VPN\s0 packet" |
| 239 | .IX Subsection "Anatomy of a VPN packet" |
238 | .IX Subsection "Anatomy of a VPN packet" |
| 240 | The exact layout and field lengths of a \s-1VPN\s0 packet is determined at |
239 | The exact layout and field lengths of a \s-1VPN\s0 packet is determined at |
| 241 | compiletime and doesn't change. The same structure is used for all |
240 | compile time and doesn't change. The same structure is used for all |
| 242 | transort protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0. |
241 | transport protocols, be it \s-1RAWIP\s0 or \s-1TCP\s0. |
| 243 | .PP |
242 | .PP |
| 244 | .Vb 3 |
243 | .Vb 3 |
| 245 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
244 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| 246 | \& | HMAC | TYPE | SRCDST | DATA | |
245 | \& | HMAC | TYPE | SRCDST | DATA | |
| 247 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
246 | \& +\-\-\-\-\-\-+\-\-\-\-\-\-+\-\-\-\-\-\-\-\-+\-\-\-\-\-\-+ |
| … | |
… | |
| 270 | .PP |
269 | .PP |
| 271 | \&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of |
270 | \&\s-1RAND\s0 is a sequence of fully random bytes, used to increase the entropy of |
| 272 | the data for encryption purposes. |
271 | the data for encryption purposes. |
| 273 | .PP |
272 | .PP |
| 274 | \&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection |
273 | \&\s-1SEQNO\s0 is a 32\-bit sequence number. It is negotiated at every connection |
| 275 | initialization and starts at some random 31 bit value. \s-1VPE\s0 currently uses |
274 | initialization and starts at some random 31 bit value. \s-1GVPE\s0 currently uses |
| 276 | a sliding window of 512 packets/sequence numbers to detect reordering, |
275 | a sliding window of 512 packets/sequence numbers to detect reordering, |
| 277 | duplication and replay attacks. |
276 | duplication and replay attacks. |
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277 | .PP |
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278 | The encryption is done on \s-1RAND+SEQNO+DATA\s0 in \s-1CBC\s0 mode with zero \s-1IV\s0 (or, |
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279 | equivalently, the \s-1IV\s0 is \s-1RAND+SEQNO\s0, encrypted with the block cipher, |
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280 | unless \s-1RAND\s0 size is decreased or increased over the default value). |
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281 | .PP |
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282 | The random prefix itself is generated by using \s-1AES\s0 in \s-1CTR\s0 mode with a |
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283 | random key and starting value, which should make them unpredictable even |
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284 | before encrypting them again. The sequence number additionally ensures |
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285 | that the \s-1IV\s0 is unique. |
| 278 | .Sh "The authentication protocol" |
286 | .SS "The authentication/key exchange protocol" |
| 279 | .IX Subsection "The authentication protocol" |
287 | .IX Subsection "The authentication/key exchange protocol" |
| 280 | Before hosts can exchange packets, they need to establish authenticity of |
288 | Before nodes can exchange packets, they need to establish authenticity of |
| 281 | the other side and a key. Every host has a private \s-1RSA\s0 key and the public |
289 | the other side and a key. Every node has a private \s-1RSA\s0 key and the public |
| 282 | \&\s-1RSA\s0 keys of all other hosts. |
290 | \&\s-1RSA\s0 keys of all other nodes. |
| 283 | .PP |
291 | .PP |
| 284 | A host establishes a simplex connection by sending the other host an |
292 | When a node wants to establish a connection to another node, it sends an |
| 285 | \&\s-1RSA\s0 encrypted challenge containing a random challenge (consisting of |
293 | RSA-OEAP-encrypted challenge and an \s-1ECDH\s0 key. The other node replies with |
| 286 | the encryption key to use when sending packets, more random data and |
294 | it's own \s-1ECDH\s0 key and a \s-1HKDF\s0 of the challange and both \s-1ECDH\s0 keys to proof |
| 287 | \&\s-1PKCS1_OAEP\s0 padding) and a random 16 byte \*(L"challenge\-id\*(R" (used to detect |
295 | it's identity. |
| 288 | duplicate auth packets). The destination host will respond by replying |
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| 289 | with an (unencrypted) \s-1RIPEMD160\s0 hash of the decrypted challenge, which |
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| 290 | will authenticate that host. The destination host will also set the |
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| 291 | outgoing encryption parameters as given in the packet. |
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| 292 | .PP |
296 | .PP |
| 293 | When the source host receives a correct auth reply (by verifying the |
297 | The remote node enganges in exactly the same protocol. When both nodes |
| 294 | hash and the id, which will expire after 120 seconds), it will start to |
298 | have exchanged their challenge and verified the response, they calculate a |
| 295 | accept data packets from the destination host. |
299 | cipher key and a \s-1HMAC\s0 key and start exchanging data packets. |
| 296 | .PP |
300 | .PP |
| 297 | This means that a host can only initate a simplex connection, telling the |
301 | In detail, the challenge consist of: |
| 298 | other side the key it has to use when it sends packets. The challenge |
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| 299 | reply is only used to set the current \s-1IP\s0 address of the other side and |
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| 300 | protocol parameters. |
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| 301 | .PP |
302 | .PP |
| 302 | This protocol is completely symmetric, so to be able to send packets the |
303 | .Vb 1 |
| 303 | destination host must send a challenge in the exact same way as already |
304 | \& RSA\-OAEP (SEQNO MAC CIPHER SALT EXTRA\-AUTH) ECDH1 |
| 304 | described (so, in essence, two simplex connections are created per host |
305 | .Ve |
| 305 | pair). |
306 | .PP |
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307 | That is, it encrypts (with the public key of the remote node) an initial |
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308 | sequence number for data packets, key material for the \s-1HMAC\s0 key, key |
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309 | material for the cipher key, a salt used by the \s-1HKDF\s0 (as shown later) and |
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310 | some extra random bytes that are unused except for authentication. It also |
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311 | sends the public key of a curve25519 exchange. |
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312 | .PP |
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313 | The remote node decrypts the \s-1RSA\s0 data, generates it's own \s-1ECDH\s0 key (\s-1ECDH2\s0), and |
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314 | replies with: |
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315 | .PP |
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316 | .Vb 1 |
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317 | \& HKDF\-Expand (HKDF\-Extract (ECDH2, RSA), ECDH1, AUTH_DIGEST_SIZE) ECDH2 |
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318 | .Ve |
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319 | .PP |
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320 | That is, it extracts from the decrypted \s-1RSA\s0 challenge, using it's \s-1ECDH\s0 |
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321 | key as salt, and then expands using the requesting node's \s-1ECDH1\s0 key. The |
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322 | resulting has is returned as a proof that the node could decrypt the \s-1RSA\s0 |
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323 | challenge data, together with the \s-1ECDH\s0 key. |
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324 | .PP |
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325 | After both nodes have done this to each other, they calculate the shared |
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326 | \&\s-1ECDH\s0 secrets, cipher and \s-1HMAC\s0 keys for the session (each |
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327 | node generates two cipher and \s-1HMAC\s0 keys, one for sending and one for |
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328 | receiving). |
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329 | .PP |
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330 | The \s-1HMAC\s0 key for sending is generated as follow: |
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331 | .PP |
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332 | .Vb 1 |
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333 | \& HMAC_KEY = HKDF\-Expand (HKDF\-Extract (REMOTE_SALT, MAC ECDH_SECRET), info, HMAC_MD_SIZE) |
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334 | .Ve |
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335 | .PP |
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336 | It extracts from \s-1MAC\s0 and \s-1ECDH_SECRET\s0 using the \fIremote\fR \s-1SALT\s0, then |
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337 | expands using a static info string. |
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338 | .PP |
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339 | The cipher key is generated in the same way, except using the \s-1CIPHER\s0 part |
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340 | of the original challenge. |
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341 | .PP |
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342 | The result of this process is to authenticate each node to the other |
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343 | node, while exchanging keys using both \s-1RSA\s0 and \s-1ECDH\s0, the latter providing |
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344 | perfect forward secrecy. |
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345 | .PP |
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346 | The protocol has been overdesigned where this was possible without |
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347 | increasing implementation complexity, in an attempt to protect against |
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348 | implementation or protocol failures. For example, if the \s-1ECDH\s0 challenge |
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349 | was found to be flawed, perfect forward secrecy would be lost, but |
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350 | the data would still be protected. Likewise, standard algorithms and |
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351 | implementations are used where possible. |
| 306 | .Sh "Retrying" |
352 | .SS "Retrying" |
| 307 | .IX Subsection "Retrying" |
353 | .IX Subsection "Retrying" |
| 308 | When there is no response to an auth request, the host will send auth |
354 | When there is no response to an auth request, the node will send auth |
| 309 | requests in bursts with an exponential backoff. After some time it will |
355 | requests in bursts with an exponential back-off. After some time it will |
| 310 | resort to \s-1PING\s0 packets, which are very small (8 bytes + protocol header) |
356 | resort to \s-1PING\s0 packets, which are very small (8 bytes + protocol header) |
| 311 | and lightweight (no \s-1RSA\s0 operations required). A host that receives ping |
357 | and lightweight (no \s-1RSA\s0 operations required). A node that receives ping |
| 312 | requests from an unconnected peer will respond by trying to create a |
358 | requests from an unconnected peer will respond by trying to create a |
| 313 | connection. |
359 | connection. |
| 314 | .PP |
360 | .PP |
| 315 | In addition to the exponential backoff, there is a global rate-limit on |
361 | In addition to the exponential back-off, there is a global rate-limit on |
| 316 | a per-IP base. It allows long bursts but will limit total packet rate to |
362 | a per-IP base. It allows long bursts but will limit total packet rate to |
| 317 | something like one control packet every ten seconds, to avoid accidental |
363 | something like one control packet every ten seconds, to avoid accidental |
| 318 | floods due to protocol problems (like a \s-1RSA\s0 key file mismatch between two |
364 | floods due to protocol problems (like a \s-1RSA\s0 key file mismatch between two |
| 319 | hosts). |
365 | nodes). |
| 320 | .PP |
366 | .PP |
| 321 | The intervals between retries are limited by the \f(CW\*(C`max\-retry\*(C'\fR |
367 | The intervals between retries are limited by the \f(CW\*(C`max\-retry\*(C'\fR |
| 322 | configuration value. A node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`always\*(C'\fR will always retry, |
368 | configuration value. A node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`always\*(C'\fR will always retry, |
| 323 | a node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`ondemand\*(C'\fR will only try (and re\-try) to connect |
369 | a node with \f(CW\*(C`connect\*(C'\fR = \f(CW\*(C`ondemand\*(C'\fR will only try (and re-try) to connect |
| 324 | as long as there are packets in the queue, usually this limits the retry |
370 | as long as there are packets in the queue, usually this limits the retry |
| 325 | period to \f(CW\*(C`max\-ttl\*(C'\fR seconds. |
371 | period to \f(CW\*(C`max\-ttl\*(C'\fR seconds. |
| 326 | .PP |
372 | .PP |
| 327 | Sending packets over the \s-1VPN\s0 will reset the retry intervals as well, which |
373 | Sending packets over the \s-1VPN\s0 will reset the retry intervals as well, which |
| 328 | means as long as somebody is trying to send packets to a given node, \s-1GVPE\s0 |
374 | means as long as somebody is trying to send packets to a given node, \s-1GVPE\s0 |
| 329 | will try to connect every few seconds. |
375 | will try to connect every few seconds. |
| 330 | .Sh "Routing and Protocol translation" |
376 | .SS "Routing and Protocol translation" |
| 331 | .IX Subsection "Routing and Protocol translation" |
377 | .IX Subsection "Routing and Protocol translation" |
| 332 | The \s-1GVPE\s0 routing algorithm is easy: there isn't much routing to speak |
378 | The \s-1GVPE\s0 routing algorithm is easy: there isn't much routing to speak |
| 333 | of: When routing packets to another node, \s-1GVPE\s0 trues the following |
379 | of: When routing packets to another node, \s-1GVPE\s0 tries the following |
| 334 | options, in order: |
380 | options, in order: |
| 335 | .IP "If the two hosts should be able to reach each other directly (common protocol, port known), then \s-1GVPE\s0 will send the packet directly to the other node." 4 |
381 | .IP "If the two nodes should be able to reach each other directly (common protocol, port known), then \s-1GVPE\s0 will send the packet directly to the other node." 4 |
| 336 | .IX Item "If the two hosts should be able to reach each other directly (common protocol, port known), then GVPE will send the packet directly to the other node." |
382 | .IX Item "If the two nodes should be able to reach each other directly (common protocol, port known), then GVPE will send the packet directly to the other node." |
| 337 | .PD 0 |
383 | .PD 0 |
| 338 | .ie n .IP "If this isn't possible (e.g. because the node doesn't have a \*(C`hostname\*(C' or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ""mediate"" between both nodes (see below)." 4 |
384 | .ie n .IP "If this isn't possible (e.g. because the node doesn't have a \*(C`hostname\*(C' or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ""mediate"" between both nodes (see below)." 4 |
| 339 | .el .IP "If this isn't possible (e.g. because the node doesn't have a \f(CW\*(C`hostname\*(C'\fR or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ``mediate'' between both nodes (see below)." 4 |
385 | .el .IP "If this isn't possible (e.g. because the node doesn't have a \f(CW\*(C`hostname\*(C'\fR or known port), but the nodes speak a common protocol and a router is available, then \s-1GVPE\s0 will ask a router to ``mediate'' between both nodes (see below)." 4 |
| 340 | .IX Item "If this isn't possible (e.g. because the node doesn't have a hostname or known port), but the nodes speak a common protocol and a router is available, then GVPE will ask a router to mediate between both nodes (see below)." |
386 | .IX Item "If this isn't possible (e.g. because the node doesn't have a hostname or known port), but the nodes speak a common protocol and a router is available, then GVPE will ask a router to mediate between both nodes (see below)." |
| 341 | .ie n .IP "If a direct connection isn't possible (no common protocols) or forbidden (\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand is able (as specified by the config file) to connect directly to the target node." 4 |
387 | .ie n .IP "If a direct connection isn't possible (no common protocols) or forbidden (\*(C`deny\-direct\*(C') and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand\fR is able (as specified by the config file) to connect directly to the target node." 4 |
| 342 | .el .IP "If a direct connection isn't possible (no common protocols) or forbidden (\f(CW\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand\fR is able (as specified by the config file) to connect directly to the target node." 4 |
388 | .el .IP "If a direct connection isn't possible (no common protocols) or forbidden (\f(CW\*(C`deny\-direct\*(C'\fR) and there are any routers, then \s-1GVPE\s0 will try to send packets to the router with the highest priority that is connected already \fIand\fR is able (as specified by the config file) to connect directly to the target node." 4 |
| 343 | .IX Item "If a direct connection isn't possible (no common protocols) or forbidden (deny-direct) and there are any routers, then GVPE will try to send packets to the router with the highest priority that is connected already and is able (as specified by the config file) to connect directly to the target node." |
389 | .IX Item "If a direct connection isn't possible (no common protocols) or forbidden (deny-direct) and there are any routers, then GVPE will try to send packets to the router with the highest priority that is connected already and is able (as specified by the config file) to connect directly to the target node." |
| 344 | .IP "If no such router exists, then \s-1GVPE\s0 will simply send the packet to the node with the highest priority available." 4 |
390 | .IP "If no such router exists, then \s-1GVPE\s0 will simply send the packet to the node with the highest priority available." 4 |
| 345 | .IX Item "If no such router exists, then GVPE will simply send the packet to the node with the highest priority available." |
391 | .IX Item "If no such router exists, then GVPE will simply send the packet to the node with the highest priority available." |
| 346 | .IP "Failing all that, the packet will be dropped." 4 |
392 | .IP "Failing all that, the packet will be dropped." 4 |
| … | |
… | |
| 351 | port number(s) to zero. It can declare other hosts as unreachable by using |
397 | port number(s) to zero. It can declare other hosts as unreachable by using |
| 352 | a config-file that disables all protocols for these other hosts. Another |
398 | a config-file that disables all protocols for these other hosts. Another |
| 353 | option is to disable all protocols on that host in the other config files. |
399 | option is to disable all protocols on that host in the other config files. |
| 354 | .PP |
400 | .PP |
| 355 | If two hosts cannot connect to each other because their \s-1IP\s0 address(es) |
401 | If two hosts cannot connect to each other because their \s-1IP\s0 address(es) |
| 356 | are not known (such as dialup hosts), one side will send a \fImediated\fR |
402 | are not known (such as dial-up hosts), one side will send a \fImediated\fR |
| 357 | connection request to a router (routers must be configured to act as |
403 | connection request to a router (routers must be configured to act as |
| 358 | routers!), which will send both the originating and the destination host |
404 | routers!), which will send both the originating and the destination host |
| 359 | a connection info request with protocol information and \s-1IP\s0 address of the |
405 | a connection info request with protocol information and \s-1IP\s0 address of the |
| 360 | other host (if known). Both hosts will then try to establish a direct |
406 | other host (if known). Both hosts will then try to establish a direct |
| 361 | connection to the other peer, which is usually possible even when both |
407 | connection to the other peer, which is usually possible even when both |
