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499 lines
20 KiB
Plaintext
499 lines
20 KiB
Plaintext
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TC: A Tor control protocol (Version 0)
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-1. Deprecation
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THIS PROTOCOL IS DEPRECATED. It is still documented here because Tor
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0.1.1.x happens to support much of it; but the support for v0 is not
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maintained, so you should expect it to rot in unpredictable ways. Support
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for v0 will be removed some time after Tor 0.1.2.
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0. Scope
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This document describes an implementation-specific protocol that is used
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for other programs (such as frontend user-interfaces) to communicate
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with a locally running Tor process. It is not part of the Tor onion
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routing protocol.
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We're trying to be pretty extensible here, but not infinitely
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forward-compatible.
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1. Protocol outline
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TC is a bidirectional message-based protocol. It assumes an underlying
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stream for communication between a controlling process (the "client") and
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a Tor process (the "server"). The stream may be implemented via TCP,
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TLS-over-TCP, a Unix-domain socket, or so on, but it must provide
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reliable in-order delivery. For security, the stream should not be
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accessible by untrusted parties.
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In TC, the client and server send typed variable-length messages to each
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other over the underlying stream. By default, all messages from the server
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are in response to messages from the client. Some client requests, however,
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will cause the server to send messages to the client indefinitely far into
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the future.
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Servers respond to messages in the order they're received.
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2. Message format
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The messages take the following format:
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Length [2 octets; big-endian]
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Type [2 octets; big-endian]
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Body [Length octets]
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Upon encountering a recognized Type, implementations behave as described in
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section 3 below. If the type is not recognized, servers respond with an
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"ERROR" message (code UNRECOGNIZED; see 3.1 below), and clients simply ignore
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the message.
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2.1. Types and encodings
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All numbers are given in big-endian (network) order.
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OR identities are given in hexadecimal, in the same format as identity key
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fingerprints, but without spaces; see tor-spec.txt for more information.
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3. Message types
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Message types are drawn from the following ranges:
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0x0000-0xEFFF : Reserved for use by official versions of this spec.
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0xF000-0xFFFF : Unallocated; usable by unofficial extensions.
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3.1. ERROR (Type 0x0000)
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Sent in response to a message that could not be processed as requested.
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The body of the message begins with a 2-byte error code. The following
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values are defined:
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0x0000 Unspecified error
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[]
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0x0001 Internal error
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[Something went wrong inside Tor, so that the client's
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request couldn't be fulfilled.]
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0x0002 Unrecognized message type
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[The client sent a message type we don't understand.]
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0x0003 Syntax error
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[The client sent a message body in a format we can't parse.]
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0x0004 Unrecognized configuration key
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[The client tried to get or set a configuration option we don't
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recognize.]
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0x0005 Invalid configuration value
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[The client tried to set a configuration option to an
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incorrect, ill-formed, or impossible value.]
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0x0006 Unrecognized byte code
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[The client tried to set a byte code (in the body) that
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we don't recognize.]
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0x0007 Unauthorized.
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[The client tried to send a command that requires
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authorization, but it hasn't sent a valid AUTHENTICATE
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message.]
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0x0008 Failed authentication attempt
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[The client sent a well-formed authorization message.]
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0x0009 Resource exhausted
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[The server didn't have enough of a given resource to
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fulfill a given request.]
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0x000A No such stream
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0x000B No such circuit
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0x000C No such OR
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The rest of the body should be a human-readable description of the error.
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In general, new error codes should only be added when they don't fall under
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one of the existing error codes.
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3.2. DONE (Type 0x0001)
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Sent from server to client in response to a request that was successfully
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completed, with no more information needed. The body is usually empty but
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may contain a message.
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3.3. SETCONF (Type 0x0002)
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Change the value of a configuration variable. The body contains a list of
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newline-terminated key-value configuration lines. An individual key-value
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configuration line consists of the key, followed by a space, followed by
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the value. The server behaves as though it had just read the key-value pair
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in its configuration file.
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The server responds with a DONE message on success, or an ERROR message on
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failure.
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When a configuration options takes multiple values, or when multiple
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configuration keys form a context-sensitive group (see below), then
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setting _any_ of the options in a SETCONF command is taken to reset all of
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the others. For example, if two ORBindAddress values are configured,
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and a SETCONF command arrives containing a single ORBindAddress value, the
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new command's value replaces the two old values.
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To _remove_ all settings for a given option entirely (and go back to its
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default value), send a single line containing the key and no value.
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3.4. GETCONF (Type 0x0003)
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Request the value of a configuration variable. The body contains one or
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more NL-terminated strings for configuration keys. The server replies
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with a CONFVALUE message.
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If an option appears multiple times in the configuration, all of its
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key-value pairs are returned in order.
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Some options are context-sensitive, and depend on other options with
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different keywords. These cannot be fetched directly. Currently there
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is only one such option: clients should use the "HiddenServiceOptions"
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virtual keyword to get all HiddenServiceDir, HiddenServicePort,
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HiddenServiceNodes, and HiddenServiceExcludeNodes option settings.
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3.5. CONFVALUE (Type 0x0004)
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Sent in response to a GETCONF message; contains a list of "Key Value\n"
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(A non-whitespace keyword, a single space, a non-NL value, a NL)
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strings.
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3.6. SETEVENTS (Type 0x0005)
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Request the server to inform the client about interesting events.
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The body contains a list of 2-byte event codes (see "event" below).
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Any events *not* listed in the SETEVENTS body are turned off; thus, sending
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SETEVENTS with an empty body turns off all event reporting.
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The server responds with a DONE message on success, and an ERROR message
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if one of the event codes isn't recognized. (On error, the list of active
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event codes isn't changed.)
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3.7. EVENT (Type 0x0006)
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Sent from the server to the client when an event has occurred and the
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client has requested that kind of event. The body contains a 2-byte
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event code followed by additional event-dependent information. Event
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codes are:
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0x0001 -- Circuit status changed
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Status [1 octet]
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0x00 Launched - circuit ID assigned to new circuit
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0x01 Built - all hops finished, can now accept streams
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0x02 Extended - one more hop has been completed
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0x03 Failed - circuit closed (was not built)
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0x04 Closed - circuit closed (was built)
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Circuit ID [4 octets]
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(Must be unique to Tor process/time)
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Path [NUL-terminated comma-separated string]
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(For extended/failed, is the portion of the path that is
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built)
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0x0002 -- Stream status changed
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Status [1 octet]
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(Sent connect=0,sent resolve=1,succeeded=2,failed=3,
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closed=4, new connection=5, new resolve request=6,
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stream detached from circuit and still retriable=7)
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Stream ID [4 octets]
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(Must be unique to Tor process/time)
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Target (NUL-terminated address-port string]
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0x0003 -- OR Connection status changed
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Status [1 octet]
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(Launched=0,connected=1,failed=2,closed=3)
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OR nickname/identity [NUL-terminated]
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0x0004 -- Bandwidth used in the last second
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Bytes read [4 octets]
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Bytes written [4 octets]
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0x0005 -- Notice/warning/error occurred
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Message [NUL-terminated]
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<obsolete: use 0x0007-0x000B instead.>
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0x0006 -- New descriptors available
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OR List [NUL-terminated, comma-delimited list of
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OR identity]
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0x0007 -- Debug message occurred
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0x0008 -- Info message occurred
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0x0009 -- Notice message occurred
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0x000A -- Warning message occurred
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0x000B -- Error message occurred
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Message [NUL-terminated]
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3.8. AUTHENTICATE (Type 0x0007)
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Sent from the client to the server. Contains a 'magic cookie' to prove
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that client is really allowed to control this Tor process. The server
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responds with DONE or ERROR.
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The format of the 'cookie' is implementation-dependent; see 4.1 below for
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information on how the standard Tor implementation handles it.
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3.9. SAVECONF (Type 0x0008)
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Sent from the client to the server. Instructs the server to write out
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its config options into its torrc. Server returns DONE if successful, or
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ERROR if it can't write the file or some other error occurs.
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3.10. SIGNAL (Type 0x0009)
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Sent from the client to the server. The body contains one byte that
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indicates the action the client wishes the server to take.
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1 (0x01) -- Reload: reload config items, refetch directory.
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2 (0x02) -- Controlled shutdown: if server is an OP, exit immediately.
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If it's an OR, close listeners and exit after 30 seconds.
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10 (0x0A) -- Dump stats: log information about open connections and
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circuits.
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12 (0x0C) -- Debug: switch all open logs to loglevel debug.
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15 (0x0F) -- Immediate shutdown: clean up and exit now.
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The server responds with DONE if the signal is recognized (or simply
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closes the socket if it was asked to close immediately), else ERROR.
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3.11. MAPADDRESS (Type 0x000A)
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Sent from the client to the server. The body contains a sequence of
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address mappings, each consisting of the address to be mapped, a single
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space, the replacement address, and a NL character.
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Addresses may be IPv4 addresses, IPv6 addresses, or hostnames.
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The client sends this message to the server in order to tell it that future
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SOCKS requests for connections to the original address should be replaced
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with connections to the specified replacement address. If the addresses
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are well-formed, and the server is able to fulfill the request, the server
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replies with a single DONE message containing the source and destination
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addresses. If request is malformed, the server replies with a syntax error
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message. The server can't fulfill the request, it replies with an internal
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ERROR message.
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The client may decline to provide a body for the original address, and
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instead send a special null address ("0.0.0.0" for IPv4, "::0" for IPv6, or
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"." for hostname), signifying that the server should choose the original
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address itself, and return that address in the DONE message. The server
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should ensure that it returns an element of address space that is unlikely
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to be in actual use. If there is already an address mapped to the
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destination address, the server may reuse that mapping.
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If the original address is already mapped to a different address, the old
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mapping is removed. If the original address and the destination address
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are the same, the server removes any mapping in place for the original
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address.
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{Note: This feature is designed to be used to help Tor-ify applications
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that need to use SOCKS4 or hostname-less SOCKS5. There are three
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approaches to doing this:
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1. Somehow make them use SOCKS4a or SOCKS5-with-hostnames instead.
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2. Use tor-resolve (or another interface to Tor's resolve-over-SOCKS
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feature) to resolve the hostname remotely. This doesn't work
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with special addresses like x.onion or x.y.exit.
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3. Use MAPADDRESS to map an IP address to the desired hostname, and then
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arrange to fool the application into thinking that the hostname
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has resolved to that IP.
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This functionality is designed to help implement the 3rd approach.}
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[XXXX When, if ever, can mappings expire? Should they expire?]
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[XXXX What addresses, if any, are safe to use?]
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3.12 GETINFO (Type 0x000B)
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Sent from the client to the server. The message body is as for GETCONF:
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one or more NL-terminated strings. The server replies with an INFOVALUE
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message.
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Unlike GETCONF, this message is used for data that are not stored in the
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Tor configuration file, but instead.
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Recognized key and their values include:
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"version" -- The version of the server's software, including the name
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of the software. (example: "Tor 0.0.9.4")
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"desc/id/<OR identity>" or "desc/name/<OR nickname>" -- the latest server
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descriptor for a given OR, NUL-terminated. If no such OR is known, the
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corresponding value is an empty string.
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"network-status" -- a space-separated list of all known OR identities.
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This is in the same format as the router-status line in directories;
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see tor-spec.txt for details.
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"addr-mappings/all"
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"addr-mappings/config"
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"addr-mappings/cache"
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"addr-mappings/control" -- a NL-terminated list of address mappings, each
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in the form of "from-address" SP "to-address". The 'config' key
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returns those address mappings set in the configuration; the 'cache'
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key returns the mappings in the client-side DNS cache; the 'control'
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key returns the mappings set via the control interface; the 'all'
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target returns the mappings set through any mechanism.
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3.13 INFOVALUE (Type 0x000C)
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Sent from the server to the client in response to a GETINFO message.
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Contains one or more items of the format:
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Key [(NUL-terminated string)]
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Value [(NUL-terminated string)]
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The keys match those given in the GETINFO message.
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3.14 EXTENDCIRCUIT (Type 0x000D)
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Sent from the client to the server. The message body contains two fields:
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Circuit ID [4 octets]
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Path [NUL-terminated, comma-delimited string of OR nickname/identity]
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This request takes one of two forms: either the Circuit ID is zero, in
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which case it is a request for the server to build a new circuit according
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to the specified path, or the Circuit ID is nonzero, in which case it is a
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request for the server to extend an existing circuit with that ID according
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to the specified path.
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If the request is successful, the server sends a DONE message containing
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a message body consisting of the four-octet Circuit ID of the newly created
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circuit.
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3.15 ATTACHSTREAM (Type 0x000E)
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Sent from the client to the server. The message body contains two fields:
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Stream ID [4 octets]
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Circuit ID [4 octets]
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This message informs the server that the specified stream should be
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associated with the specified circuit. Each stream may be associated with
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at most one circuit, and multiple streams may share the same circuit.
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Streams can only be attached to completed circuits (that is, circuits that
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have sent a circuit status 'built' event).
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If the circuit ID is 0, responsibility for attaching the given stream is
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returned to Tor.
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{Implementation note: By default, Tor automatically attaches streams to
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circuits itself, unless the configuration variable
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"__LeaveStreamsUnattached" is set to "1". Attempting to attach streams
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via TC when "__LeaveStreamsUnattached" is false may cause a race between
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Tor and the controller, as both attempt to attach streams to circuits.}
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3.16 POSTDESCRIPTOR (Type 0x000F)
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Sent from the client to the server. The message body contains one field:
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Descriptor [NUL-terminated string]
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This message informs the server about a new descriptor.
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The descriptor, when parsed, must contain a number of well-specified
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fields, including fields for its nickname and identity.
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If there is an error in parsing the descriptor, the server must send an
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appropriate error message. If the descriptor is well-formed but the server
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chooses not to add it, it must reply with a DONE message whose body
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explains why the server was not added.
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3.17 FRAGMENTHEADER (Type 0x0010)
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Sent in either direction. Used to encapsulate messages longer than 65535
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bytes in length.
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Underlying type [2 bytes]
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Total Length [4 bytes]
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Data [Rest of message]
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A FRAGMENTHEADER message MUST be followed immediately by a number of
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FRAGMENT messages, such that lengths of the "Data" fields of the
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FRAGMENTHEADER and FRAGMENT messages add to the "Total Length" field of the
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FRAGMENTHEADER message.
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Implementations MUST NOT fragment messages of length less than 65536 bytes.
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Implementations MUST be able to process fragmented messages that not
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optimally packed.
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3.18 FRAGMENT (Type 0x0011)
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Data [Entire message]
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See FRAGMENTHEADER for more information
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3.19 REDIRECTSTREAM (Type 0x0012)
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Sent from the client to the server. The message body contains two fields:
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Stream ID [4 octets]
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Address [variable-length, NUL-terminated.]
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Tells the server to change the exit address on the specified stream. No
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remapping is performed on the new provided address.
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To be sure that the modified address will be used, this event must be sent
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after a new stream event is received, and before attaching this stream to
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a circuit.
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3.20 CLOSESTREAM (Type 0x0013)
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Sent from the client to the server. The message body contains three
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fields:
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Stream ID [4 octets]
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Reason [1 octet]
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Flags [1 octet]
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Tells the server to close the specified stream. The reason should be
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one of the Tor RELAY_END reasons given in tor-spec.txt. Flags is not
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used currently. Tor may hold the stream open for a while to flush
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any data that is pending.
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3.21 CLOSECIRCUIT (Type 0x0014)
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Sent from the client to the server. The message body contains two
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fields:
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Circuit ID [4 octets]
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Flags [1 octet]
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Tells the server to close the specified circuit. If the LSB of the flags
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field is nonzero, do not close the circuit unless it is unused.
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4. Implementation notes
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4.1. Authentication
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By default, the current Tor implementation trusts all local users.
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If the 'CookieAuthentication' option is true, Tor writes a "magic cookie"
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file named "control_auth_cookie" into its data directory. To authenticate,
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the controller must send the contents of this file.
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If the 'HashedControlPassword' option is set, it must contain the salted
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hash of a secret password. The salted hash is computed according to the
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S2K algorithm in RFC 2440 (OpenPGP), and prefixed with the s2k specifier.
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This is then encoded in hexadecimal, prefixed by the indicator sequence
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"16:". Thus, for example, the password 'foo' could encode to:
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16:660537E3E1CD49996044A3BF558097A981F539FEA2F9DA662B4626C1C2
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++++++++++++++++**^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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salt hashed value
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indicator
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You can generate the salt of a password by calling
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'tor --hash-password <password>'
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or by using the example code in the Python and Java controller libraries.
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To authenticate under this scheme, the controller sends Tor the original
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secret that was used to generate the password.
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4.2. Don't let the buffer get too big.
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If you ask for lots of events, and 16MB of them queue up on the buffer,
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the Tor process will close the socket.
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