control-spec.txt 19 KB

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  1. $Id$
  2. TC: A Tor control protocol
  3. 0. Scope
  4. This document describes an implementation-specific protocol that is used
  5. for other programs (such as frontend user-interfaces) to communicate
  6. with a locally running Tor process. It is not part of the Tor onion
  7. routing protocol.
  8. We're trying to be pretty extensible here, but not infinitely
  9. forward-compatible.
  10. 1. Protocol outline
  11. TC is a bidirectional message-based protocol. It assumes an underlying
  12. stream for communication between a controlling process (the "client") and
  13. a Tor process (the "server"). The stream may be implemented via TCP,
  14. TLS-over-TCP, a Unix-domain socket, or so on, but it must provide
  15. reliable in-order delivery. For security, the stream should not be
  16. accessible by untrusted parties.
  17. In TC, the client and server send typed variable-length messages to each
  18. other over the underlying stream. By default, all messages from the server
  19. are in response to messages from the client. Some client requests, however,
  20. will cause the server to send messages to the client indefinitely far into
  21. the future.
  22. Servers respond to messages in the order they're received.
  23. 2. Message format
  24. The messages take the following format:
  25. Length [2 octets; big-endian]
  26. Type [2 octets; big-endian]
  27. Body [Length octets]
  28. Upon encountering a recognized Type, implementations behave as described in
  29. section 3 below. If the type is not recognized, servers respond with an
  30. "ERROR" message (code UNRECOGNIZED; see 3.1 below), and clients simply ignore
  31. the message.
  32. 2.1. Types and encodings
  33. All numbers are given in big-endian (network) order.
  34. OR identities are given in hexadecimal, in the same format as identity key
  35. fingerprints, but without spaces; see tor-spec.txt for more information.
  36. 3. Message types
  37. Message types are drawn from the following ranges:
  38. 0x0000-0xEFFF : Reserved for use by official versions of this spec.
  39. 0xF000-0xFFFF : Unallocated; usable by unofficial extensions.
  40. 3.1. ERROR (Type 0x0000)
  41. Sent in response to a message that could not be processed as requested.
  42. The body of the message begins with a 2-byte error code. The following
  43. values are defined:
  44. 0x0000 Unspecified error
  45. []
  46. 0x0001 Internal error
  47. [Something went wrong inside Tor, so that the client's
  48. request couldn't be fulfilled.]
  49. 0x0002 Unrecognized message type
  50. [The client sent a message type we don't understand.]
  51. 0x0003 Syntax error
  52. [The client sent a message body in a format we can't parse.]
  53. 0x0004 Unrecognized configuration key
  54. [The client tried to get or set a configuration option we don't
  55. recognize.]
  56. 0x0005 Invalid configuration value
  57. [The client tried to set a configuration option to an
  58. incorrect, ill-formed, or impossible value.]
  59. 0x0006 Unrecognized byte code
  60. [The client tried to set a byte code (in the body) that
  61. we don't recognize.]
  62. 0x0007 Unauthorized.
  63. [The client tried to send a command that requires
  64. authorization, but it hasn't sent a valid AUTHENTICATE
  65. message.]
  66. 0x0008 Failed authentication attempt
  67. [The client sent a well-formed authorization message.]
  68. 0x0009 Resource exhausted
  69. [The server didn't have enough of a given resource to
  70. fulfill a given request.]
  71. 0x000A No such stream
  72. 0x000B No such circuit
  73. 0x000C No such OR
  74. The rest of the body should be a human-readable description of the error.
  75. In general, new error codes should only be added when they don't fall under
  76. one of the existing error codes.
  77. 3.2. DONE (Type 0x0001)
  78. Sent from server to client in response to a request that was successfully
  79. completed, with no more information needed. The body is usually empty but
  80. may contain a message.
  81. 3.3. SETCONF (Type 0x0002)
  82. Change the value of a configuration variable. The body contains a list of
  83. newline-terminated key-value configuration lines. An individual key-value
  84. configuration line consists of the key, followed by a space, followed by
  85. the value. The server behaves as though it had just read the key-value pair
  86. in its configuration file.
  87. The server responds with a DONE message on success, or an ERROR message on
  88. failure.
  89. When a configuration options takes multiple values, or when multiple
  90. configuration keys form a context-sensitive group (see below), then
  91. setting _any_ of the options in a SETCONF command is taken to reset all of
  92. the others. For example, if two ORBindAddress values are configured,
  93. and a SETCONF command arrives containing a single ORBindAddress value, the
  94. new command's value replaces the two old values.
  95. To _remove_ all settings for a given option entirely (and go back to its
  96. default value), send a single line containing the key and no value.
  97. 3.4. GETCONF (Type 0x0003)
  98. Request the value of a configuration variable. The body contains one or
  99. more NL-terminated strings for configuration keys. The server replies
  100. with a CONFVALUE message.
  101. If an option appears multiple times in the configuration, all of its
  102. key-value pairs are returned in order.
  103. Some options are context-sensitive, and depend on other options with
  104. different keywords. These cannot be fetched directly. Currently there
  105. is only one such option: clients should use the "HiddenServiceOptions"
  106. virtual keyword to get all HiddenServiceDir, HiddenServicePort,
  107. HiddenServiceNodes, and HiddenServiceExcludeNodes option settings.
  108. 3.5. CONFVALUE (Type 0x0004)
  109. Sent in response to a GETCONF message; contains a list of "Key Value\n"
  110. (A non-whitespace keyword, a single space, a non-NL value, a NL)
  111. strings.
  112. 3.6. SETEVENTS (Type 0x0005)
  113. Request the server to inform the client about interesting events.
  114. The body contains a list of 2-byte event codes (see "event" below).
  115. Any events *not* listed in the SETEVENTS body are turned off; thus, sending
  116. SETEVENTS with an empty body turns off all event reporting.
  117. The server responds with a DONE message on success, and an ERROR message
  118. if one of the event codes isn't recognized. (On error, the list of active
  119. event codes isn't changed.)
  120. 3.7. EVENT (Type 0x0006)
  121. Sent from the server to the client when an event has occurred and the
  122. client has requested that kind of event. The body contains a 2-byte
  123. event code followed by additional event-dependent information. Event
  124. codes are:
  125. 0x0001 -- Circuit status changed
  126. Status [1 octet]
  127. 0x00 Launched - circuit ID assigned to new circuit
  128. 0x01 Built - all hops finished, can now accept streams
  129. 0x02 Extended - one more hop has been completed
  130. 0x03 Failed - circuit closed (was not built)
  131. 0x04 Closed - circuit closed (was built)
  132. Circuit ID [4 octets]
  133. (Must be unique to Tor process/time)
  134. Path [NUL-terminated comma-separated string]
  135. (For extended/failed, is the portion of the path that is
  136. built)
  137. 0x0002 -- Stream status changed
  138. Status [1 octet]
  139. (Sent connect=0,sent resolve=1,succeeded=2,failed=3,
  140. closed=4, new connection=5, new resolve request=6,
  141. stream detached from circuit and still retriable=7)
  142. Stream ID [4 octets]
  143. (Must be unique to Tor process/time)
  144. Target (NUL-terminated address-port string]
  145. 0x0003 -- OR Connection status changed
  146. Status [1 octet]
  147. (Launched=0,connected=1,failed=2,closed=3)
  148. OR nickname/identity [NUL-terminated]
  149. 0x0004 -- Bandwidth used in the last second
  150. Bytes read [4 octets]
  151. Bytes written [4 octets]
  152. 0x0005 -- Notice/warning/error occurred
  153. Message [NUL-terminated]
  154. <obsolete: use 0x0007-0x000B instead.>
  155. 0x0006 -- New descriptors available
  156. OR List [NUL-terminated, comma-delimited list of
  157. OR identity]
  158. 0x0007 -- Debug message occurred
  159. 0x0008 -- Info message occurred
  160. 0x0009 -- Notice message occurred
  161. 0x000A -- Warning message occurred
  162. 0x000B -- Error message occurred
  163. Message [NUL-terminated]
  164. 3.8. AUTHENTICATE (Type 0x0007)
  165. Sent from the client to the server. Contains a 'magic cookie' to prove
  166. that client is really the admin for this Tor process. The server responds
  167. with DONE or ERROR.
  168. 3.9. SAVECONF (Type 0x0008)
  169. Sent from the client to the server. Instructs the server to write out
  170. its config options into its torrc. Server returns DONE if successful, or
  171. ERROR if it can't write the file or some other error occurs.
  172. 3.10. SIGNAL (Type 0x0009)
  173. Sent from the client to the server. The body contains one byte that
  174. indicates the action the client wishes the server to take.
  175. 1 (0x01) -- Reload: reload config items, refetch directory.
  176. 2 (0x02) -- Controlled shutdown: if server is an OP, exit immediately.
  177. If it's an OR, close listeners and exit after 30 seconds.
  178. 10 (0x0A) -- Dump stats: log information about open connections and
  179. circuits.
  180. 12 (0x0C) -- Debug: switch all open logs to loglevel debug.
  181. 15 (0x0F) -- Immediate shutdown: clean up and exit now.
  182. The server responds with DONE if the signal is recognized (or simply
  183. closes the socket if it was asked to close immediately), else ERROR.
  184. 3.11. MAPADDRESS (Type 0x000A)
  185. Sent from the client to the server. The body contains a sequence of
  186. address mappings, each consisting of the address to be mapped, a single
  187. space, the replacement address, and a NL character.
  188. Addresses may be IPv4 addresses, IPv6 addresses, or hostnames.
  189. The client sends this message to the server in order to tell it that future
  190. SOCKS requests for connections to the original address should be replaced
  191. with connections to the specified replacement address. If the addresses
  192. are well-formed, and the server is able to fulfill the request, the server
  193. replies with a single DONE message containing the source and destination
  194. addresses. If request is malformed, the server replies with a syntax error
  195. message. The server can't fulfill the request, it replies with an internal
  196. ERROR message.
  197. The client may decline to provide a body for the original address, and
  198. instead send a special null address ("0.0.0.0" for IPv4, "::0" for IPv6, or
  199. "." for hostname), signifying that the server should choose the original
  200. address itself, and return that address in the DONE message. The server
  201. should ensure that it returns an element of address space that is unlikely
  202. to be in actual use. If there is already an address mapped to the
  203. destination address, the server may reuse that mapping.
  204. If the original address is already mapped to a different address, the old
  205. mapping is removed. If the original address and the destination address
  206. are the same, the server removes any mapping in place for the original
  207. address.
  208. {Note: This feature is designed to be used to help Tor-ify applications
  209. that need to use SOCKS4 or hostname-less SOCKS5. There are three
  210. approaches to doing this:
  211. 1. Somehow make them use SOCKS4a or SOCKS5-with-hostnames instead.
  212. 2. Use tor-resolve (or another interface to Tor's resolve-over-SOCKS
  213. feature) to resolve the hostname remotely. This doesn't work
  214. with special addresses like x.onion or x.y.exit.
  215. 3. Use MAPADDRESS to map an IP address to the desired hostname, and then
  216. arrange to fool the application into thinking that the hostname
  217. has resolved to that IP.
  218. This functionality is designed to help implement the 3rd approach.}
  219. [XXXX When, if ever, can mappings expire? Should they expire?]
  220. [XXXX What addresses, if any, are safe to use?]
  221. 3.12 GETINFO (Type 0x000B)
  222. Sent from the client to the server. The message body is as for GETCONF:
  223. one or more NL-terminated strings. The server replies with an INFOVALUE
  224. message.
  225. Unlike GETCONF, this message is used for data that are not stored in the
  226. Tor configuration file, but instead.
  227. Recognized key and their values include:
  228. "version" -- The version of the server's software, including the name
  229. of the software. (example: "Tor 0.0.9.4")
  230. "desc/id/<OR identity>" or "desc/name/<OR nickname>" -- the latest server
  231. descriptor for a given OR, NUL-terminated. If no such OR is known, the
  232. corresponding value is an empty string.
  233. "network-status" -- a space-separated list of all known OR identities.
  234. This is in the same format as the router-status line in directories;
  235. see tor-spec.txt for details.
  236. "addr-mappings/all"
  237. "addr-mappings/config"
  238. "addr-mappings/cache"
  239. "addr-mappings/control" -- a NL-terminated list of address mappings, each
  240. in the form of "from-address" SP "to-address". The 'config' key
  241. returns those address mappings set in the configuration; the 'cache'
  242. key returns the mappings in the client-side DNS cache; the 'control'
  243. key returns the mappings set via the control interface; the 'all'
  244. target returns the mappings set through any mechanism.
  245. 3.13 INFOVALUE (Type 0x000C)
  246. Sent from the server to the client in response to a GETINFO message.
  247. Contains one or more items of the format:
  248. Key [(NUL-terminated string)]
  249. Value [(NUL-terminated string)]
  250. The keys match those given in the GETINFO message.
  251. 3.14 EXTENDCIRCUIT (Type 0x000D)
  252. Sent from the client to the server. The message body contains two fields:
  253. Circuit ID [4 octets]
  254. Path [NUL-terminated, comma-delimited string of OR nickname/identity]
  255. This request takes one of two forms: either the Circuit ID is zero, in
  256. which case it is a request for the server to build a new circuit according
  257. to the specified path, or the Circuit ID is nonzero, in which case it is a
  258. request for the server to extend an existing circuit with that ID according
  259. to the specified path.
  260. If the request is successful, the server sends a DONE message containing
  261. a message body consisting of the four-octet Circuit ID of the newly created
  262. circuit.
  263. 3.15 ATTACHSTREAM (Type 0x000E)
  264. Sent from the client to the server. The message body contains two fields:
  265. Stream ID [4 octets]
  266. Circuit ID [4 octets]
  267. This message informs the server that the specified stream should be
  268. associated with the specified circuit. Each stream may be associated with
  269. at most one circuit, and multiple streams may share the same circuit.
  270. Streams can only be attached to completed circuits (that is, circuits that
  271. have sent a circuit status 'built' event).
  272. If the circuit ID is 0, responsibility for attaching the given stream is
  273. returned to Tor.
  274. {Implementation note: By default, Tor automatically attaches streams to
  275. circuits itself, unless the configuration variable
  276. "__LeaveStreamsUnattached" is set to "1". Attempting to attach streams
  277. via TC when "__LeaveStreamsUnattached" is false may cause a race between
  278. Tor and the controller, as both attempt to attach streams to circuits.}
  279. 3.16 POSTDESCRIPTOR (Type 0x000F)
  280. Sent from the client to the server. The message body contains one field:
  281. Descriptor [NUL-terminated string]
  282. This message informs the server about a new descriptor.
  283. The descriptor, when parsed, must contain a number of well-specified
  284. fields, including fields for its nickname and identity.
  285. If there is an error in parsing the descriptor, the server must send an
  286. appropriate error message. If the descriptor is well-formed but the server
  287. chooses not to add it, it must reply with a DONE message whose body
  288. explains why the server was not added.
  289. 3.17 FRAGMENTHEADER (Type 0x0010)
  290. Sent in either direction. Used to encapsulate messages longer than 65535
  291. bytes in length.
  292. Underlying type [2 bytes]
  293. Total Length [4 bytes]
  294. Data [Rest of message]
  295. A FRAGMENTHEADER message MUST be followed immediately by a number of
  296. FRAGMENT messages, such that lengths of the "Data" fields of the
  297. FRAGMENTHEADER and FRAGMENT messages add to the "Total Length" field of the
  298. FRAGMENTHEADER message.
  299. Implementations MUST NOT fragment messages of length less than 65536 bytes.
  300. Implementations MUST be able to process fragmented messages that not
  301. optimally packed.
  302. 3.18 FRAGMENT (Type 0x0011)
  303. Data [Entire message]
  304. See FRAGMENTHEADER for more information
  305. 3.19 REDIRECTSTREAM (Type 0x0012)
  306. Sent from the client to the server. The message body contains two fields:
  307. Stream ID [4 octets]
  308. Address [variable-length, NUL-terminated.]
  309. Tells the server to change the exit address on the specified stream. No
  310. remapping is performed on the new provided address.
  311. To be sure that the modified address will be used, this event must be sent
  312. after a new stream event is received, and before attaching this stream to
  313. a circuit.
  314. 3.20 CLOSESTREAM (Type 0x0013)
  315. Sent from the client to the server. The message body contains three
  316. fields:
  317. Stream ID [4 octets]
  318. Reason [1 octet]
  319. Flags [1 octet]
  320. Tells the server to close the specified stream. The reason should be
  321. one of the Tor RELAY_END reasons given in tor-spec.txt. Flags is not
  322. used currently. Tor may hold the stream open for a while to flush
  323. any data that is pending.
  324. 3.21 CLOSECIRCUIT (Type 0x0014)
  325. Sent from the client to the server. The message body contains two
  326. fields:
  327. Circuit ID [4 octets]
  328. Flags [1 octet]
  329. Tells the server to close the specified circuit. If the LSB of the flags
  330. field is nonzero, do not close the circuit unless it is unused.
  331. 4. Implementation notes
  332. 4.1. There are four ways we could authenticate, for now:
  333. 1) Listen on 127.0.0.1; trust all local users.
  334. 2) Write a named socket in tor's data-directory or in some other location;
  335. rely on the OS to ensure that only authorized users can open it. (NOTE:
  336. the Linux unix(7) man page suggests that some BSDs don't enforce
  337. authorization.) If the OS has named sockets, and implements
  338. authentication, trust all users who can read Tor's data directory.
  339. 3) Write a random magic cookie to the FS in Tor's data-directory; use that
  340. magic cookie for authentication. Trust all users who can read Tor's data
  341. directory.
  342. 4) Store a salted-and-hashed passphrase in Tor's configuration. Use the
  343. passphrase for authentication. Trust all users who know the passphrase.
  344. On Win32, our only options are 1, 3, and 4. Since the semantics for 2
  345. and 3 are so similar, we chose to not support 2, and just always bind
  346. on 127.0.0.1. We've implemented 1, 3, and 4.
  347. By default, the Tor client accepts authentication approach #1. If
  348. the controller wants Tor to demand more authentication, it should use
  349. setconf and saveconf to configure Tor to demand more next time.
  350. 4.2. Don't let the buffer get too big.
  351. If you ask for lots of events, and 16MB of them queue up on the buffer,
  352. the Tor process will close the socket.