| 1 | .\" -*-nroff-*- |
| 2 | .\". |
| 3 | .de hP |
| 4 | .IP |
| 5 | \h'-\w'\fB\\$1\ \fP'u'\fB\\$1\ \fP\c |
| 6 | .. |
| 7 | .de VS |
| 8 | .sp 1 |
| 9 | .RS |
| 10 | .nf |
| 11 | .ft B |
| 12 | .. |
| 13 | .de VE |
| 14 | .ft R |
| 15 | .fi |
| 16 | .RE |
| 17 | .sp 1 |
| 18 | .. |
| 19 | .ie t \{\ |
| 20 | . ds o \(bu |
| 21 | . ds ss \s8\u |
| 22 | . ds se \d\s0 |
| 23 | . if \n(.g \{\ |
| 24 | . fam P |
| 25 | . \} |
| 26 | .\} |
| 27 | .el \{\ |
| 28 | . ds o o |
| 29 | . ds ss ^ |
| 30 | . ds se |
| 31 | .\} |
| 32 | .TH tripe 8 "10 February 2001" "Straylight/Edgeware" "TrIPE: Trivial IP Encryption" |
| 33 | .SH "NAME" |
| 34 | tripe \- a simple VPN daemon |
| 35 | .SH "SYNOPSIS" |
| 36 | .B tripe |
| 37 | .RB [ \-D ] |
| 38 | .RB [ \-d |
| 39 | .IR dir ] |
| 40 | .RB [ \-b |
| 41 | .IR addr ] |
| 42 | .RB [ \-p |
| 43 | .IR port ] |
| 44 | .RB [ \-n |
| 45 | .IR tunnel ] |
| 46 | .br |
| 47 | |
| 48 | .RB [ \-U |
| 49 | .IR user ] |
| 50 | .RB [ \-G |
| 51 | .IR group ] |
| 52 | .RB [ \-a |
| 53 | .IR socket ] |
| 54 | .RB [ \-T |
| 55 | .IR trace-opts ] |
| 56 | .br |
| 57 | |
| 58 | .RB [ \-k |
| 59 | .IR priv-keyring ] |
| 60 | .RB [ \-K |
| 61 | .IR pub-keyring ] |
| 62 | .RB [ \-t |
| 63 | .IR key-tag ] |
| 64 | .SH "DESCRIPTION" |
| 65 | The |
| 66 | .B tripe |
| 67 | program is a server which can provide strong IP-level encryption and |
| 68 | authentication between co-operating hosts. The program and its protocol |
| 69 | are deliberately very simple, to make analysing them easy and to help |
| 70 | build trust rapidly in the system. |
| 71 | .SS "Overview" |
| 72 | The |
| 73 | .B tripe |
| 74 | server manages a number of secure connections to other `peer' hosts. |
| 75 | Each daemon is given a private key of its own, and a file of public keys |
| 76 | for the peers with which it is meant to communicate. It is responsible |
| 77 | for negotiating sets of symmetric keys with its peers, and for |
| 78 | encrypting, encapsulating and sending IP packets to its peers, and |
| 79 | decrypting, checking and de-encapsulating packets it receives from |
| 80 | them. |
| 81 | .PP |
| 82 | When the server starts, it creates a Unix-domain socket on which it |
| 83 | listens for administration commands. It also logs warnings and |
| 84 | diagnostic information to the programs connected to its admin socket. |
| 85 | Clients connected to the socket can add new peers, and remove or find |
| 86 | out about existing peers. The textual protocol used to give the |
| 87 | .B tripe |
| 88 | server admin commands is described in |
| 89 | .BR tripe\-admin (5). |
| 90 | A client program |
| 91 | .BR tripectl (1) |
| 92 | is provided to allow commands to be sent to the server either |
| 93 | interactively or by simple scripts. |
| 94 | .SS "Command-line arguments" |
| 95 | If not given any command-line arguments, |
| 96 | .B tripe |
| 97 | will initialize by following these steps: |
| 98 | .hP 1. |
| 99 | It sets the directory named by the |
| 100 | .B TRIPEDIR |
| 101 | environment variable (or |
| 102 | .B "@configdir@" |
| 103 | if the variable is unset) as the current directory. |
| 104 | .hP 2. |
| 105 | It acquires a UDP socket with an arbitrary kernel-selected port number. |
| 106 | It will use this socket to send and receive all communications with its |
| 107 | peer servers. The port chosen may be discovered by means of the |
| 108 | .B PORT |
| 109 | admin command (see |
| 110 | .BR tripe\-admin (5)). |
| 111 | .hP 3. |
| 112 | It loads the private key with the tag or type name |
| 113 | .B tripe\-dh |
| 114 | from the Catacomb-format file |
| 115 | .BR keyring , |
| 116 | and loads the file |
| 117 | .B keyring.pub |
| 118 | ready for extracting the public keys of peers as they're introduced. |
| 119 | (The format of these files is described in |
| 120 | .BR keyring (5). |
| 121 | They are maintained using the program |
| 122 | .BR key (1) |
| 123 | provided with the Catacomb distribution.) |
| 124 | .hP 4. |
| 125 | It creates and listens to the Unix-domain socket |
| 126 | .BR tripesock . |
| 127 | .PP |
| 128 | Following this, the server enters its main loop, accepting admin |
| 129 | connections and obeying any administrative commands, and communicating |
| 130 | with peers. It also treats its standard input and standard output |
| 131 | streams as an admin connection, reading commands from standard input and |
| 132 | writing responses and diagnostics messages to standard output. Finally, |
| 133 | it will reload keys from its keyring files if it notices that they've |
| 134 | changed (it checks inode number and modification time) \- there's no |
| 135 | need to send a signal. |
| 136 | .PP |
| 137 | Much of this behaviour may be altered by giving |
| 138 | .B tripe |
| 139 | suitable command-line options: |
| 140 | .TP |
| 141 | .B "\-h, \-\-help" |
| 142 | Writes a brief description of the command-line options available to |
| 143 | standard output and exits with status 0. |
| 144 | .TP |
| 145 | .B "\-v, \-\-version" |
| 146 | Writes |
| 147 | .BR tripe 's |
| 148 | version number to standard output and exits with status 0. |
| 149 | .TP |
| 150 | .B "\-u, \-\-usage" |
| 151 | Writes a brief usage summary to standard output and exits with status 0. |
| 152 | .TP |
| 153 | .B "\-\-tunnels" |
| 154 | Writes to standard output a list of the configured tunnel drivers, one |
| 155 | per line, and exits with status 0. This is intended for the use of the |
| 156 | start-up script, so that it can check that it will actually work. |
| 157 | .TP |
| 158 | .B "\-D, \-\-daemon" |
| 159 | Dissociates from its terminal and starts running in the background after |
| 160 | completing the initialization procedure described above. If running as |
| 161 | a daemon, |
| 162 | .B tripe |
| 163 | will not read commands from standard input or write diagnostics to |
| 164 | standard output. A better way to start |
| 165 | .B tripe |
| 166 | in the background is with |
| 167 | .BR tripectl (1). |
| 168 | .TP |
| 169 | .BI "\-d, \-\-directory=" dir |
| 170 | Makes |
| 171 | .I dir |
| 172 | the current directory. The default directory to change to is given by |
| 173 | the environment variable |
| 174 | .BR TRIPEDIR ; |
| 175 | if that's not specified, a default default of |
| 176 | .B "@configdir@" |
| 177 | is used. Give a current directory of |
| 178 | .B . |
| 179 | if you don't want it to change directory at all. |
| 180 | .TP |
| 181 | .BI "\-b, \-\-bind-address="addr |
| 182 | Bind the UDP socket to IP address |
| 183 | .I addr |
| 184 | rather than the default of |
| 185 | .BR INADDR_ANY . |
| 186 | This is useful if your main globally-routable IP address is one you want |
| 187 | to tunnel through the VPN. |
| 188 | .TP |
| 189 | .BI "\-p, \-\-port=" port |
| 190 | Use the specified UDP port for all communications with peers, rather |
| 191 | than an arbitarary kernel-assigned port. |
| 192 | .TP |
| 193 | .BI "\-n, \-\-tunnel=" tunnel |
| 194 | Use the specified tunnel driver for new peers by default. |
| 195 | .TP |
| 196 | .BI "\-U, \-\-setuid=" user |
| 197 | Set uid to that of |
| 198 | .I user |
| 199 | (either a user name or integer uid) after initialization. Also set gid |
| 200 | to |
| 201 | .IR user 's |
| 202 | primary group, unless overridden by a |
| 203 | .B \-G |
| 204 | option. |
| 205 | .TP |
| 206 | .BI "\-G, \-\-setgid=" group |
| 207 | Set gid to that of |
| 208 | .I group |
| 209 | (either a group name or integer gid) after initialization. |
| 210 | .TP |
| 211 | .BI "\-k, \-\-priv\-keyring=" file |
| 212 | Reads the private key from |
| 213 | .I file |
| 214 | rather than the default |
| 215 | .BR keyring . |
| 216 | .TP |
| 217 | .BI "\-K, \-\-pub\-keyring=" file |
| 218 | Reads public keys from |
| 219 | .I file |
| 220 | rather than the default |
| 221 | .BR keyring.pub . |
| 222 | This can be the same as the private keyring, but that's not recommended. |
| 223 | .TP |
| 224 | .BI "\-t, \-\-tag=" tag |
| 225 | Uses the private key whose tag or type is |
| 226 | .I tag |
| 227 | rather than the default |
| 228 | .BR tripe\-dh . |
| 229 | .TP |
| 230 | .BI "\-a, \-\-admin\-socket=" socket |
| 231 | Accept admin connections to a Unix-domain socket named |
| 232 | .IR socket . |
| 233 | The default socket, if this option isn't specified, is given by the |
| 234 | environment variable |
| 235 | .BR TRIPESOCK ; |
| 236 | if that's not set either, then a default default of |
| 237 | .B "@socketdir@/tripesock" |
| 238 | is used instead. |
| 239 | .TP |
| 240 | .BI "\-T, \-\-trace=" trace-opts |
| 241 | Allows the enabling or disabling of various internal diagnostics. See |
| 242 | below for the list of options. |
| 243 | .SS "Setting up a VPN with tripe" |
| 244 | The |
| 245 | .B tripe |
| 246 | server identifies peers by name. While it's |
| 247 | .I possible |
| 248 | for each host to maintain its own naming system for its peers, this is |
| 249 | likely to lead to confusion, and it's more sensible to organize a naming |
| 250 | system that works everywhere. How you manage this naming is up to you. |
| 251 | The only restriction on the format of names is that they must be valid |
| 252 | Catacomb key tags, since this is how |
| 253 | .B tripe |
| 254 | identifies which public key to use for a particular peer: they may not |
| 255 | contain whitespace characters, or a colon |
| 256 | .RB ` : ' |
| 257 | or dot |
| 258 | .RB ` . ', |
| 259 | .PP |
| 260 | Allocating IP addresses for VPNs can get quite complicated. I'll |
| 261 | attempt to illustrate with a relatively simple example. Our objective |
| 262 | will be to set up a virtual private network between two sites of |
| 263 | .BR example.com . |
| 264 | The two sites are using distinct IP address ranges from the private |
| 265 | address space described in RFC1918: site A is using addresses from |
| 266 | 10.0.1.0/24 and site B is using 10.0.2.0/24. Each site has a gateway |
| 267 | host set up with both an address on the site's private network, and an |
| 268 | externally-routable address from the public IP address space. Site A's |
| 269 | gateway machine, |
| 270 | .BR alice , |
| 271 | has the addresses 10.0.1.1 and 200.0.1.1; site B's gateway is |
| 272 | .B bob |
| 273 | and has addresses 10.0.2.1 and 200.0.2.1. |
| 274 | .hP 1. |
| 275 | Install |
| 276 | .B tripe |
| 277 | on both of the gateway hosts. Create the directory |
| 278 | .BR /var/lib/tripe . |
| 279 | .hP 2. |
| 280 | On |
| 281 | .BR alice , |
| 282 | make |
| 283 | .B /var/lib/tripe |
| 284 | the current directory and generate a Diffie-Hellman group: |
| 285 | .RS |
| 286 | .VS |
| 287 | key add \-adh\-param \-LS \-b2048 \-B256 \e |
| 288 | \-eforever \-tparam tripe\-dh\-param |
| 289 | .VE |
| 290 | (See |
| 291 | .BR key (1) |
| 292 | from the Catacomb distribution for details about the |
| 293 | .B key |
| 294 | command.) Also generate a private key for |
| 295 | .BR alice : |
| 296 | .VS |
| 297 | key add \-adh \-pparam \-talice \e |
| 298 | \-e"now + 1 year" tripe\-dh |
| 299 | .VE |
| 300 | Extract the group parameters and |
| 301 | .BR alice 's |
| 302 | public key to |
| 303 | .I separate |
| 304 | files, and put the public key in |
| 305 | .BR keyring.pub : |
| 306 | .VS |
| 307 | key extract param param |
| 308 | key extract \-f\-secret alice.pub alice |
| 309 | key \-kkeyring.pub merge alice.pub |
| 310 | .VE |
| 311 | Send the files |
| 312 | .B param |
| 313 | and |
| 314 | .B alice.pub |
| 315 | to |
| 316 | .B bob |
| 317 | in some secure way (e.g., in PGP-signed email, or by using SSH), so that |
| 318 | you can be sure they've not been altered in transit. |
| 319 | .RE |
| 320 | .hP 3. |
| 321 | On |
| 322 | .B bob |
| 323 | now, make |
| 324 | .B /var/lib/tripe |
| 325 | the current directory, and import the key material from |
| 326 | .BR alice : |
| 327 | .RS |
| 328 | .VS |
| 329 | key merge param |
| 330 | key \-kkeyring.pub merge alice.pub |
| 331 | .VE |
| 332 | Generate a private key for |
| 333 | .B bob |
| 334 | and extract the public half, as before: |
| 335 | .VS |
| 336 | key add \-adh \-pparam \-tbob \e |
| 337 | \-e"now + 1 year" tripe\-dh |
| 338 | key extract \-f\-secret bob.pub bob |
| 339 | key \-kkeyring.pub merge bob.pub |
| 340 | .VE |
| 341 | and send |
| 342 | .B bob.pub |
| 343 | back to |
| 344 | .B alice |
| 345 | using some secure method. |
| 346 | .RE |
| 347 | .hP 4 |
| 348 | On |
| 349 | .BR alice , |
| 350 | merge |
| 351 | .B bob 's |
| 352 | key into the public keyring. Now, on each host, run |
| 353 | .RS |
| 354 | .VS |
| 355 | key \-kkeyring.pub fingerprint |
| 356 | .VE |
| 357 | and check that the hashes match. If the two sites have separate |
| 358 | administrators, they should read the hashes to each other over the |
| 359 | telephone (assuming that they can recognize each other's voices). |
| 360 | .RE |
| 361 | .hP 5. |
| 362 | Start the |
| 363 | .B tripe |
| 364 | servers up. Run |
| 365 | .RS |
| 366 | .VS |
| 367 | tripectl \-slD |
| 368 | .VE |
| 369 | on each of |
| 370 | .B alice |
| 371 | and |
| 372 | .BR bob . |
| 373 | .RE |
| 374 | .hP 6. |
| 375 | To get |
| 376 | .B alice |
| 377 | talking to |
| 378 | .BR bob , |
| 379 | run this shell script (or one like it): |
| 380 | .RS |
| 381 | .VS |
| 382 | #! /bin/sh |
| 383 | |
| 384 | tripectl add bob 200.0.2.1 4070 |
| 385 | ifname=`tripectl ifname bob` |
| 386 | ifconfig $ifname 10.0.1.1 pointopoint 10.0.2.1 |
| 387 | route add -net \e |
| 388 | 10.0.2.0 netmask 255.255.255.0 \e |
| 389 | gw 10.0.2.1 |
| 390 | .VE |
| 391 | Read |
| 392 | .BR ifconfig (8) |
| 393 | and |
| 394 | .BR route (8) |
| 395 | to find out about your system's variants of these commands. The |
| 396 | versions shown above assume a Linux system. |
| 397 | Run a similar script on |
| 398 | .BR bob , |
| 399 | to tell its |
| 400 | .B tripe |
| 401 | server to talk to |
| 402 | .BR alice . |
| 403 | .RE |
| 404 | .hP 7. |
| 405 | Congratulations. The two servers will exchange keys and begin sending |
| 406 | packets almost immediately. You've set up a virtual private network. |
| 407 | .SS "Using elliptic curve keys" |
| 408 | The |
| 409 | .B tripe |
| 410 | server can use elliptic curve Diffie-Hellman for key exchange, rather |
| 411 | than traditional integer Diffie-Hellman. Given current public |
| 412 | knowledge, elliptic curves can provide similar or better security to |
| 413 | systems based on integer discrete log problems, faster, and with less |
| 414 | transmitted data. It's a matter of controversy whether this will |
| 415 | continue to be the case. The author uses elliptic curves. |
| 416 | .PP |
| 417 | The server works out which it |
| 418 | should be doing based on the key type, which is either |
| 419 | .B tripe\-dh |
| 420 | for standard Diffie-Hellman, or |
| 421 | .B tripe\-ec |
| 422 | for elliptic curves. To create elliptic curve keys, say something like |
| 423 | .VS |
| 424 | key add \-aec\-param \-Cnist-p192 \-eforever \e |
| 425 | \-tparam tripe\-ec\-param |
| 426 | .VE |
| 427 | to construct a parameters key, using your preferred elliptic curve in |
| 428 | the |
| 429 | .B \-C |
| 430 | option (see |
| 431 | .BR key (1) |
| 432 | for details); and create the private keys by |
| 433 | .VS |
| 434 | key add \-aec \-pparam \-talice \e |
| 435 | \-e"now + 1 year" tripe\-ec |
| 436 | .VE |
| 437 | Now start |
| 438 | .B tripe |
| 439 | with the |
| 440 | .B \-ttripe\-ec |
| 441 | option, and all should be well. |
| 442 | .SS "Using other symmetric algorithms" |
| 443 | The default symmetric algorithms |
| 444 | .B tripe |
| 445 | uses are Blowfish (by Schneier) for symmetric encryption, and RIPEMD-160 |
| 446 | (by Dobbertin, Bosselaers and Preneel) for hashing and as a MAC (in HMAC |
| 447 | mode, designed by Bellare, Canetti and Krawczyk). These can all be |
| 448 | overridden by setting attributes on your private key, as follows. |
| 449 | .TP |
| 450 | .B cipher |
| 451 | Names the symmetric encryption scheme to use. The default is |
| 452 | .BR blowfish\-cbc . |
| 453 | .TP |
| 454 | .B hash |
| 455 | Names the hash function to use. The default is |
| 456 | .BR rmd160 . |
| 457 | .TP |
| 458 | .B mac |
| 459 | Names the message authentication code to use. The name of the MAC may |
| 460 | be followed by a |
| 461 | .RB ` / ' |
| 462 | and the desired tag length in bits. The default is |
| 463 | .IB hash \-hmac |
| 464 | at half the underlying hash function's output length. |
| 465 | .TP |
| 466 | .B mgf |
| 467 | A `mask-generation function', used in the key-exchange. The default is |
| 468 | .IB hash \-mgf |
| 469 | and there's no good reason to change it. |
| 470 | .SS "Using SLIP interfaces" |
| 471 | Though not for the faint of heart, it is possible to get |
| 472 | .B tripe |
| 473 | to read and write network packets to a pair of file descriptors using |
| 474 | SLIP encapsulation. No fancy header compression of any kind is |
| 475 | supported. |
| 476 | .PP |
| 477 | Two usage modes are supported: a preallocation system, whereby SLIP |
| 478 | interfaces are created and passed to the |
| 479 | .B tripe |
| 480 | server at startup; and a dynamic system, where the server runs a script |
| 481 | to allocate a new SLIP interface when it needs one. It is possible to |
| 482 | use a mixture of these two modes, starting |
| 483 | .B tripe |
| 484 | with a few preallocated interfaces and having it allocate more |
| 485 | dynamically as it needs them. |
| 486 | .PP |
| 487 | The behaviour of |
| 488 | .BR tripe 's |
| 489 | SLIP driver is controlled by the |
| 490 | .B TRIPE_SLIPIF |
| 491 | environment variable. The server will not create SLIP tunnels if this |
| 492 | variable is not defined. The variable's value is a colon-delimited list |
| 493 | of preallocated interfaces, followed optionally by the filename of a |
| 494 | script to run to dynamically allocate more interfaces. |
| 495 | .PP |
| 496 | A static allocation entry has the form |
| 497 | .IR infd [ \c |
| 498 | .BI , outfd \c |
| 499 | .RB ] \c |
| 500 | .BI = \c |
| 501 | .IR ifname , |
| 502 | If the |
| 503 | .I outfd |
| 504 | is omitted, the same file descriptor is used for input and output. |
| 505 | .PP |
| 506 | The dynamic allocation script must be named by an absolute or relative |
| 507 | pathname, beginning with |
| 508 | .RB ` / ' |
| 509 | or |
| 510 | .RB ` . '. |
| 511 | The server will pass the script an argument, which is the name of the |
| 512 | peer for which the interface is being created. The script should |
| 513 | allocate a new SLIP interface (presumably by creating a pty pair), |
| 514 | configure it appropriately, and write the interface's name to its |
| 515 | standard output, followed by a newline. It should then read and write |
| 516 | SLIP packets on its stdin and stdout. The script's stdin will be closed |
| 517 | when the interface is no longer needed, and the server will attempt to |
| 518 | send it a |
| 519 | .B SIGTERM |
| 520 | signal (though this may fail if the script runs with higher privileges |
| 521 | than the server). |
| 522 | .PP |
| 523 | The output file descriptor should not block unless it really needs to: |
| 524 | the |
| 525 | .B tripe |
| 526 | daemon assumes that it won't, and will get wedged waiting for it to |
| 527 | accept output. |
| 528 | .SS "About the name" |
| 529 | The program's name is |
| 530 | .BR tripe , |
| 531 | all in lower-case. The name of the protocol it uses is `TrIPE', with |
| 532 | four capital letters and one lower-case. The name stands for `Trivial |
| 533 | IP Encryption'. |
| 534 | .SH "BUGS" |
| 535 | The code hasn't been audited. It may contain security bugs. If you |
| 536 | find one, please inform the author |
| 537 | .IR immediately . |
| 538 | .SH "SEE ALSO" |
| 539 | .BR key (1), |
| 540 | .BR tripectl (1), |
| 541 | .BR tripe\-admin (5). |
| 542 | .PP |
| 543 | .IR "The Trivial IP Encryption Protocol" , |
| 544 | .IR "The Wrestlers Protocol" . |
| 545 | .SH "AUTHOR" |
| 546 | Mark Wooding, <mdw@distorted.org.uk> |