hexchat

0. Protocol Overview This protocol uses an xmpp chat service as a means to
forward tcp traffic from one computer to another. It listens on a port on one
computer and forwards data through a chat server to another computer logged into
the same chat server.


1. Motivation Many countries that censor their citizens' internet access allow
access to xmpp chat servers such as google chat. With the appropriate software,
these chat servers can be used to connect and relay traffic to tor bridges.
Since most xmpp servers support encryption, it would be difficult stop tor
traffic from being relayed through xmpp chat servers without blocking access to
the chat server itself.


2. Connecting
a. The client sends a connection request to the server.

The connection request will be in the form of an IQ if the client knows the
server's full JID (user@server/resource). Otherwise, it will be in the form of a
message. Enclosed in the message/IQ is information concerning the source
ip:port, the ip:port the server should connect to, and a list of JIDs that the
client can be reached by.

b. The server acknowledges the connection request

The server indicates whether the connection succeeded or failed in an IQ stanza.
If the connection succeeded, the server sends a list of JIDs that it can be
reached by in this IQ stanza. The IQ also contains stanzas that uniquely
identify the connection by source ip:port and destination ip:port.


4. Data Exchange
a. Data is read from a socket

When data is read, it is sent in an IQ stanza. The data itself is base 64 and
enclosed in a data stanza. The IQ also contains stanzas that uniquely identify
the connection by source ip:port and destination ip:port.

b. Data is recieved from the chat server

The data is decoded from base 64 and sent to the appropriate socket.

5. Disconnecting
a. A disconnect request is sent

Disconnect requests are sent in IQ stanzas. The IQ also contains stanzas that
uniquely identify the connection by source ip:port and destination ip:port.


6. Error handling

When a bot sends XML to a user that is not logged in, the chat server replies
in the recipient's stead with an error message. When a bot receives such an
error message, it disconnects and sends disconnect requests to a different JID
(acquired from the list if JIDs given during the connection phase) until the
message goes through or it runs out of alternative JIDs.

9. Acknowledgments Thanks to asn, xnyhps, and the other tor developers for
encoraging this idea and all of the useful feedback.