[tor-dev] bananaphone obfsproxy module

[George Kadianakis]

David Stainton <dstainton415 at gmail.com> writes:

> Hi,
>
> Yeah... I should add a doc string to the BaseTransport __init__
> explaining that it runs upon connect.
>
> OK yesterday I implemented transport class method called setup()...
> The BananaphoneTransport overrides setup()... storing the markov model
> in a class attribute.
> I had to modify pyobfsproxy.py and run the class setup() method after
> the external cli args are parsed.
>
> I made it work for external cli mode... by making pyobfsproxy.py run
> the setup method for each transport after
> args.validation_function(args) runs... because the setup method needs
> some args to read the corpus file and build the markov model.
>
> What should I do to get arguments passed to obfsproxy when running in
> managed mode?
>

Hm. Good question.

You probably want to go to obfsproxy/managed/server.py and
obfsproxy/managed/client.py and place a strategic
run_transport_setup() hook. I would place it before the
launch_transport_listener() call. You might also need to use
obfsproxy/transports/get_transport_class() somewhere in there.

Another nice thing would be if you could pass the pt_config struct in
setup(), so that transports can use pt_config elements during
initialization. As an example, see how obfs2 configures its
shared-secret in its __init__ using getServerTransportOptions(). That
could be done in its setup(), I think.

Does this make sense? If you don't want to do this coding, I can do it
at some point next week.

Cheers!

(
And while I'm on it, let me tell you about the different ways that you
can pass parameters to obfsproxy. I wanted to document this somewhere,
and this thread seems like a good excuse :)

- External mode:
  You can pass global parameters to external mode transports by using
  the register_external_mode_cli() and validate_external_mode_cli()
  functions.

- Managed mode:
  - Global parameters:
    These are parameters that are passed to obfsproxy on startup.

    - Server:
      On the server-side we can pass global parameters to obfsproxy by
      using the TOR_PT_SERVER_TRANSPORT_OPTIONS environment
      variable. Obfsproxy exposes those parameters using the
      transport_config struct and
      obfsproxy/common/transport_config.py:getServerTransportOptions .
    - Client:
      On the client-side we don't have a way to pass global parameters
      to obfsproxy yet. If we ever need to, we can do it with
      environment variables here too.

  - Per-connection parameters:
    These are parameters which are supposed to be different for each
    connection. An example of such a parameter can be a shared-secret
    used for a specific bridge connection.
    
    - Server:
      On the server-side we don't have a way to pass per-connection
      parameters at the moment.
    - Client:
      On the client-side we pass per-connection parameters using the
      SOCKS handshake as a covert channel. Transports can retrieve these
      parameters using the handle_socks_args() method.
)