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tor/doc/control-spec.txt
Nick Mathewson 6602098e03 Describe how to detect v0 or v1 protocol 
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$Id$
TC: A Tor control protocol (Version 1)
0 Scope
This document describes an implementation-specific protocol that is used
for other programs (such as frontend user-interfaces) to communicate with a
locally running Tor process. It is not part of the Tor onion routing
protocol.
This protocol replaces version 0 of TC, which is now deprecated. For
reference, TC is described in "control-spec-v0.txt". Implementors are
recommended to avoid using TC directly, but instead to use a library that
can easily be updated to use the newer protocol.
1 Protocol outline
TC is a bidirectional message-based protocol. It assumes an underlying
stream for communication between a controlling process (the "client"
or "controller") and a Tor process (or "server"). The stream may be
implemented via TCP, TLS-over-TCP, a Unix-domain socket, or so on,
but it must provide reliable in-order delivery. For security, the
stream should not be accessible by untrusted parties.
In TC, the client and server send typed messages to each other over the
underlying stream. The client sends "commands" and the server sends
"replies".
By default, all messages from the server are in response to messages from
the client. Some client requests, however, will cause the server to send
messages to the client indefinitely far into the future. Such
"asynchronous" replies are marked as such.
Servers respond to messages in the order messages are received.
2 Message format
2.1 Description format
The message formats listed below use ABNF as described in RFC2234.
The protocol itself is loosely based on SMTP (see RFC 2821).
We use the following nonterminals from RFC2822: atom, qcontent
We define the following general-use nonterminals:
String = DQUOTE *qcontent DQUOTE
There are explicitly no limits on line length. All 8-bit characters are
permitted unless explicitly disallowed.
2.2 Commands from controller to Tor
Command = Keyword Arguments CRLF / "+" Keyword Arguments CRLF Data
Keyword = 1*ALPHA
Arguments = *(SP / VCHAR)
Specific commands and their arguments are described below in section 3.
2.3 Replies from Tor to the controller
Reply = *(MidReplyLine / DataReplyLine) EndReplyLine
MidReplyLine = "-" ReplyLine
DataReplyLine = "+" ReplyLine Data
EndReplyLine = SP ReplyLine
ReplyLine = StatusCode [ SP ReplyText ] CRLF
ReplyText = XXXX
StatusCode = XXXX
Specific replies are mentioned below in section 3, and described more fully
in section 4.
2.4 General-use tokens
; Identifiers for servers.
ServerID = Nickname / Fingerprint
Nickname = 1*19 NicknameChar
NicknameChar = "a"-"z" / "A"-"Z" / "0" - "9"
Fingerprint = "$" 40*HEXDIG
; Unique identifiers for streams or circuits. Currently, Tor only
; uses digits, but this may change
StreamID = 1*16 IDChar
CircuitID = 1*16 IDChar
IDChar = ALPHA / DIGIT
Address = ip4-address / ip6-address / hostname (XXXX Define these)
; A "Data" section is a sequence of octets concluded by the terminating
; sequence CRLF "." CRLF. The terminating sequence may not appear in the
; body of the data. Leading periods on lines in the data are escaped with
; an additional leading period as in RFC2821 section 4.5.2
Data = *DataLine "." CRLF
DataLine = CRLF / "." 1*LineItem CRLF/ NonDotItem *LineItem CRLF
LineItem = NonCR / 1*CR NonCRLF
NonDotItem = NonDotCR / 1*CR NonCRLF
3 Commands
All commands and other keywords are case-insensitive.
3.1 SETCONF
Change the value of one or more configuration variables. The syntax is:
"SETCONF" 1*(SP keyword ["=" String]) CRLF
Tor behaves as though it had just read each of the key-value pairs
from its configuration file. Keywords with no corresponding values have
their configuration values reset to their defaults. SETCONF is
all-or-nothing: if there is an error in any of the configuration settings,
Tor sets none of them.
Tor responds with a "250 configuration values set" reply on success.
Tor responds with a "513 syntax error in configuration values" reply on
syntax error, or a "553 impossible configuration setting" reply on a
semantic error.
When a configuration option takes multiple values, or when multiple
configuration keys form a context-sensitive group (see GETCONF below), then
setting _any_ of the options in a SETCONF command is taken to reset all of
the others. For example, if two ORBindAddress values are configured, and a
SETCONF command arrives containing a single ORBindAddress value, the new
command's value replaces the two old values.
To _remove_ all settings for a given option entirely (and go back to its
default value), send a single line containing the key and no value.
3.2 GETCONF
Request the value of a configuration variable. The syntax is:
"GETCONF" 1*(SP keyword) CRLF
If all of the listed keywords exist in the Tor configuration, Tor replies
with a series of reply lines of the form:
250 keyword=value
If any option is set to a 'default' value semantically different from an
empty string, Tor may reply with a reply line of the form:
250 keyword
If some of the listed keywords can't be found, Tor replies with a
"552 unknown configuration keyword" message.
If an option appears multiple times in the configuration, all of its
key-value pairs are returned in order.
Some options are context-sensitive, and depend on other options with
different keywords. These cannot be fetched directly. Currently there
is only one such option: clients should use the "HiddenServiceOptions"
virtual keyword to get all HiddenServiceDir, HiddenServicePort,
HiddenServiceNodes, and HiddenServiceExcludeNodes option settings.
3.3 SETEVENTS
Request the server to inform the client about interesting events. The
syntax is:
"SETEVENTS" *(SP EventCode) CRLF
EventCode = "CIRC" / "STREAM" / "ORCONN" / "BW" / "DEBUG" /
"INFO" / "NOTICE" / "WARN" / "ERR" / "NEWDESC" / "ADDRMAP"
[XXX We should have an "ADDRESSMAP" event to hear when we learn
about dns resolves, etc, so the controller can keep synced. -RD]
Any events *not* listed in the SETEVENTS line are turned off; thus, sending
SETEVENTS with an empty body turns off all event reporting.
The server responds with a "250 OK" reply on success, and a "552
Unrecognized event" reply if one of the event codes isn't recognized. (On
error, the list of active event codes isn't changed.)
3.4 AUTHENTICATE
Sent from the client to the server. The syntax is:
"AUTHENTICATE" SP 1*HEXDIG / QuotedString CRLF
The server responds with "250 OK" on success or "515 Bad authentication" if
the authentication cookie is incorrect.
The format of the 'cookie' is implementation-dependent; see 5.1 below for
information on how the standard Tor implementation handles it.
If Tor requires authentication and the controller has not yet sent an
AUTHENTICATE message, Tor sends a "514 authentication required" reply to
any other kind of message.
3.5 SAVECONF
Sent from the client to the server. The syntax is:
"SAVECONF" CRLF
Instructs the server to write out its config options into its torrc. Server
returns "250 OK" if successful, or "551 Unable to write configuration
to disk" if it can't write the file or some other error occurs.
3.6 SIGNAL
Sent from the client to the server. The syntax is:
"SIGNAL" SP Signal CRLF
Signal = "RELOAD" / "SHUTDOWN" / "DUMP" / "DEBUG" / "HALT" /
"HUP" / "INT" / "USR1" / "USR2" / "TERM"
The meaning of the signals are:
RELOAD -- Reload: reload config items, refetch directory. (like HUP)
SHUTDOWN -- Controlled shutdown: if server is an OP, exit immediately.
If it's an OR, close listeners and exit after 30 seconds.
(like INT)
DUMP -- Dump stats: log information about open connections and
circuits. (like USR1)
DEBUG -- Debug: switch all open logs to loglevel debug. (like USR2)
HALT -- Immediate shutdown: clean up and exit now. (like TERM)
The server responds with "250 OK" if the signal is recognized (or simply
closes the socket if it was asked to close immediately), or "552
Unrecognized signal" if the signal is unrecognized.
3.7 MAPADDRESS
Sent from the client to the server. The syntax is:
"MAPADDRESS" 1*(Address "=" Address SP) CRLF
The first address in each pair is an "original" address; the second is a
"replacement" address. The client sends this message to the server in
order to tell it that future SOCKS requests for connections to the original
address should be replaced with connections to the specified replacement
address. If the addresses are well-formed, and the server is able to
fulfill the request, the server replies with a 250 message:
250-OldAddress1=NewAddress1
250 OldAddress2=NewAddress2
containing the source and destination addresses. If request is malformed,
the server replies with "512 syntax error in command argument". If the server
can't fulfill the request, it replies with "451 resource exhausted."
The client may decline to provide a body for the original address, and
instead send a special null address ("0.0.0.0" for IPv4, "::0" for IPv6, or
"." for hostname), signifying that the server should choose the original
address itself, and return that address in the reply. The server
should ensure that it returns an element of address space that is unlikely
to be in actual use. If there is already an address mapped to the
destination address, the server may reuse that mapping.
If the original address is already mapped to a different address, the old
mapping is removed. If the original address and the destination address
are the same, the server removes any mapping in place for the original
address.
Example:
C: MAPADDRESS 0.0.0.0=tor.eff.org 1.2.3.4=tor.freehaven.net
S: 250-127.192.10.10=tor.eff.org
S: 250 1.2.3.4=tor.freehaven.net
{Note: This feature is designed to be used to help Tor-ify applications
that need to use SOCKS4 or hostname-less SOCKS5. There are three
approaches to doing this:
1. Somehow make them use SOCKS4a or SOCKS5-with-hostnames instead.
2. Use tor-resolve (or another interface to Tor's resolve-over-SOCKS
feature) to resolve the hostname remotely. This doesn't work
with special addresses like x.onion or x.y.exit.
3. Use MAPADDRESS to map an IP address to the desired hostname, and then
arrange to fool the application into thinking that the hostname
has resolved to that IP.
This functionality is designed to help implement the 3rd approach.}
Mappings set by the controller last until the Tor process exits:
they never expire. If the controller wants the mapping to last only
a certain time, then it must explicitly un-map the address when that
time has elapsed.
3.8 GETINFO
Sent from the client to the server. The syntax is as for GETCONF:
"GETINFO" 1*(SP keyword) CRLF
one or more NL-terminated strings. The server replies with an INFOVALUE
message.
Unlike GETCONF, this message is used for data that are not stored in the Tor
configuration file, and that may be longer than a single line. On success,
one ReplyLine is sent for each requested value, followed by a final 250 OK
ReplyLine. If a value fits on a single line, the format is:
250-keyword=value
If avalue must be split over multiple lines, the format is:
250+keyword=
value
.
Recognized key and their values include:
"version" -- The version of the server's software, including the name
of the software. (example: "Tor 0.0.9.4")
"desc/id/<OR identity>" or "desc/name/<OR nickname>" -- the latest server
descriptor for a given OR, NUL-terminated. If no such OR is known, the
corresponding value is an empty string.
"network-status" -- a space-separated list of all known OR identities.
This is in the same format as the router-status line in directories;
see tor-spec.txt for details.
"addr-mappings/all"
"addr-mappings/config"
"addr-mappings/cache"
"addr-mappings/control" -- a space-separated list of address mappings, each
in the form of "from-address=to-address". The 'config' key
returns those address mappings set in the configuration; the 'cache'
key returns the mappings in the client-side DNS cache; the 'control'
key returns the mappings set via the control interface; the 'all'
target returns the mappings set through any mechanism.
"circuit-status"
A series of lines as for a circuit status event. Each line is of the form:
CircuitID SP CircStatus SP Path CRLF
"stream-status"
A series of lines as for a stream status event. Each is of the form:
StreamID SP StreamStatus SP CircID SP Target CRLF
"orconn-status"
A series of lines as for an OR connection status event. Each is of the
form:
ServerID SP ORStatus CRLF
Examples:
C: GETINFO version desc/name/moria1
S: 250+desc/name/moria=
S: [Descriptor for moria]
S: .
S: 250-version=Tor 0.1.1.0-alpha-cvs
S: 250 OK
3.9 EXTENDCIRCUIT
Sent from the client to the server. The format is:
"EXTENDCIRCUIT" SP CircuitID SP ServerID *("," ServerID) CRLF
This request takes one of two forms: either the Circuit ID is zero, in
which case it is a request for the server to build a new circuit according
to the specified path, or the Circuit ID is nonzero, in which case it is a
request for the server to extend an existing circuit with that ID according
to the specified path.
If the request is successful, the server sends a reply containing a message
body consisting of the Circuit ID of the (maybe newly created) circuit.
The syntax is "250" SP "EXTENDED" SP CircuitID CRLF.
3.10 ATTACHSTREAM
Sent from the client to the server. The syntax is:
"ATTACHSTREAM" SP StreamID SP CircuitID CRLF
This message informs the server that the specified stream should be
associated with the specified circuit. Each stream may be associated with
at most one circuit, and multiple streams may share the same circuit.
Streams can only be attached to completed circuits (that is, circuits that
have sent a circuit status 'BUILT' event or are listed as built in a
GETINFO circuit-status request).
If the circuit ID is 0, responsibility for attaching the given stream is
returned to Tor.
Tor responds with "250 OK" if it can attach the stream, 552 if the circuit
or stream didn't exist, or 551 if the stream couldn't be attached for
another reason.
{Implementation note: By default, Tor automatically attaches streams to
circuits itself, unless the configuration variable
"__LeaveStreamsUnattached" is set to "1". Attempting to attach streams
via TC when "__LeaveStreamsUnattached" is false may cause a race between
Tor and the controller, as both attempt to attach streams to circuits.}
3.11 POSTDESCRIPTOR
Sent from the client to the server. The syntax is:
"+POSTDESCRIPTOR" CRLF Descriptor CRLF "." CRLF
This message informs the server about a new descriptor.
The descriptor, when parsed, must contain a number of well-specified
fields, including fields for its nickname and identity.
If there is an error in parsing the descriptor, the server must send a "554
Invalid descriptor" reply. If the descriptor is well-formed but the server
chooses not to add it, it must reply with a 251 message whose body explains
why the server was not added. If the descriptor is added, Tor replies with
"250 OK".
3.12 REDIRECTSTREAM
Sent from the client to the server. The syntax is:
"REDIRECTSTREAM" SP StreamID SP Address CRLF
Tells the server to change the exit address on the specified stream. No
remapping is performed on the new provided address.
To be sure that the modified address will be used, this event must be sent
after a new stream event is received, and before attaching this stream to
a circuit.
Tor replies with "250 OK" on success.
3.13 CLOSESTREAM
Sent from the client to the server. The syntax is:
"CLOSESTREAM" SP StreamID SP Reason *(SP Flag) CRLF
Tells the server to close the specified stream. The reason should be one
of the Tor RELAY_END reasons given in tor-spec.txt, as a decimal. Flags is
not used currently; Tor servers SHOULD ignore unrecognized flags. Tor may
hold the stream open for a while to flush any data that is pending.
3.14 CLOSECIRCUIT
The syntax is:
CLOSECIRCUIT SP CircuitID *(SP Flag) CRLF
Flag = "IfUnused"
Tells the server to close the specified circuit. If "IfUnused" is
provided, do not close the circuit unless it is unused.
Other flags may be defined in the future; Tor SHOULD ignore unrecognized
flags.
4 Replies
Reply codes follow the same 3-character format as used by SMTP, with the
first character defining a status, the second character defining a
subsystem, and the third designating fine-grained information.
The TC protocol currently uses the following first characters:
2yz Positive Completion Reply
The command was successful; a new request can be started.
4yz Temporary Negative Completion reply
The command was unsuccessful but might be reattempted later.
5yz Permanent Negative Completion Reply
The command was unsuccessful; the client should not try exactly
that sequence of commands again.
6yz Asynchronous Reply
Sent out-of-order in response to an earlier SETEVENTS command.
The following second characters are used:
x0z Syntax
Sent in response to ill-formed or nonsensical commands.
x1z Protocol
Refers to operations of the Tor Control protocol.
x5z Tor
Refers to actual operations of Tor system.
The following codes are defined:
250 OK
251 Operation was unnecessary
[Tor has declined to perform the operation, but no harm was done.]
451 Resource exhausted
500 Syntax error: protocol
510 Unrecognized command
511 Unimplemented command
512 Syntax error in command argument
513 Unrecognized command argument
514 Authentication required
515 Bad authentication
550 Unspecified Tor error
551 Internal error
[Something went wrong inside Tor, so that the client's
request couldn't be fulfilled.]
552 Unrecognized entity
[A configuration key, a stream ID, circuit ID, event,
mentioned in the command did not actually exist.]
553 Invalid configuration value
[The client tried to set a configuration option to an
incorrect, ill-formed, or impossible value.]
554 Invalid descriptor
555 Unmanaged entity
650 Asynchronous event notification
Unless specified to have specific contents, the human-readable messages
in error replies should not be relied upon to match those in this document.
4.1 Asynchronous events
These replies can be sent after a corresponding SETEVENTS command has been
received. They will not be interleaved with other Reply elements, but they
can appear between a command and its corresponding reply. For example,
this sequence is possible:
C: SETEVENTS CIRC
S: 250 OK
C: GETCONFIG SOCKSPORT ORPORT
S: 650 CIRC 1000 EXTENDED moria1,moria2
S: 250-SOCKSPORT=9050
S: 250 ORPORT=0
But this sequence is disallowed:
C: SETEVENTS CIRC
S: 250 OK
C: GETCONFIG SOCKSPORT ORPORT
S: 250-SOCKSPORT=9050
S: 650 CIRC 1000 EXTENDED moria1,moria2
S: 250 ORPORT=0
Clients SHOULD tolerate more arguments in an asynchonous reply than
expected, and SHOULD tolerate more lines in an asynchronous reply than
expected. For instance, a client that expects a CIRC message like:
650 CIRC 1000 EXTENDED moria1,moria2
should tolerate:
650+CIRC 1000 EXTENDED moria1,moria2 0xBEEF
650-EXTRAMAGIC=99
650 ANONYMITY=high
4.1.1 Circuit status changed
The syntax is:
"650" SP "CIRC" SP CircuitID SP CircStatus SP Path
CircStatus =
"LAUNCHED" / ; circuit ID assigned to new circuit
"BUILT" / ; all hops finished, can now accept streams
"EXTENDED" / ; one more hop has been completed
"FAILED" / ; circuit closed (was not built)
"CLOSED" ; circuit closed (was built)
Path = ServerID *("," ServerID)
4.1.2. Stream status changed
The syntax is:
"650" SP "STREAM" SP StreamID SP StreamStatus SP CircID SP Target SP
StreamStatus =
"NEW" / ; New request to connect
"NEWRESOLVE" / ; New request to resolve an address
"SENTCONNECT" / ; Sent a connect cell along a circuit
"SENTRESOLVE" / ; Sent a resolve cell along a circuit
"SUCCEEDED" / ; Received a reply; stream established
"FAILED" / ; Stream failed and not retriable.
"CLOSED" / ; Stream closed
"DETACHED" ; Detached from circuit; still retriable.
Target = Address ":" Port
The circuit ID designates which circuit this stream is attached to. If
the stream is unattached, the circuit ID "0" is given.
4.1.3 OR Connection status changed
The syntax is:
"650" SP "ORCONN" SP ServerID SP ORStatus
ORStatus = "LAUNCHED" / "CONNECTED" / "FAILED" / "CLOSED"
4.1.3 Bandwidth used in the last second
The syntax is:
"650" SP "BW" SP BytesRead SP BytesWritten
BytesRead = 1*DIGIT
BytesWritten = 1*DIGIT
4.1.4 Log message
The syntax is:
"650" SP Severity SP ReplyText
or
"650+" Severity CRLF Data
Severity = "DEBUG" / "INFO" / "NOTICE" / "WARN"/ "ERR"
4.1.5 New descriptors available
Syntax:
"650" SP "NEWDESC" 1*(SP ServerID)
4.1.6 New Address mapping
Syntax:
"650" SP "ADDRMAP" SP Address SP Address SP Expiry
Expiry = DQOUTE ISOTime DQUOTE / "NEVER"
5. Implementation notes
5.1. Authentication
By default, the current Tor implementation trusts all local users.
If the 'CookieAuthentication' option is true, Tor writes a "magic cookie"
file named "control_auth_cookie" into its data directory. To authenticate,
the controller must send the contents of this file.
If the 'HashedControlPassword' option is set, it must contain the salted
hash of a secret password. The salted hash is computed according to the
S2K algorithm in RFC 2440 (OpenPGP), and prefixed with the s2k specifier.
This is then encoded in hexadecimal, prefixed by the indicator sequence
"16:". Thus, for example, the password 'foo' could encode to:
16:660537E3E1CD49996044A3BF558097A981F539FEA2F9DA662B4626C1C2
++++++++++++++++**^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
salt hashed value
indicator
You can generate the salt of a password by calling
'tor --hash-password <password>'
or by using the example code in the Python and Java controller libraries.
To authenticate under this scheme, the controller sends Tor the original
secret that was used to generate the password.
5.2. Don't let the buffer get too big.
If you ask for lots of events, and 16MB of them queue up on the buffer,
the Tor process will close the socket.
5.3. Backward compatibility
For backward compatibility with the "version 0" control protocol, Tor checks
whether the third octet the first command is zero. If it is, Tor
assumes that version 0 is in use. This feature is deprecated, and will be
removed in the 0.1.2.x Tor development series.
In order to detect which version of the protocol is supported controllers
should send the sequence [00 00 0D 0A]. This is a valid and unrecognized
command in both protocol versions, and implementations can detect which
error they have received.
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