Commit 7c3c5198 authored by Philipp Winter's avatar Philipp Winter
Browse files

Generate a password if the bridge operator didn't. 

Generally, we require a password (the UniformDH shared secret) which is set by
the bridge operator using "ServerTransportOptions" in Tor's torrc.  Since some
bridge operators won't bother taking care of that, we want a fallback mechanism
which silently generates and publishes a password if ServerTransportOptions is
not used.  We (ab)use obfsproxy's get_public_server_options() which is meant to
sanitise parameters.  We, however, use it to add the password parameter if it's
not there.
parent 5e3fb32d

scramblesuit.py

+44 −6
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ import obfsproxy.common.log as logging 


import random

import base64

import yaml



import probdist

import mycrypto
@@ -101,6 +102,10 @@ class ScrambleSuitTransport( base.BaseTransport ): 


    @classmethod

    def setup( cls, transportConfig ):

        """

        Called once when obfsproxy starts.

        """



        util.setStateLocation(transportConfig.getStateLocation())



        cls.weAreClient = transportConfig.weAreClient
@@ -111,14 +116,47 @@ class ScrambleSuitTransport( base.BaseTransport ): 
        # shared secret from the server transport options.

        if cls.weAreServer and not cls.weAreExternal:

            cfg  = transportConfig.getServerTransportOptions()

            if "password" not in cfg:

                raise base.PluggableTransportError(

                    "Couldn't find 'password' in server transport options")



            if cfg and "password" in cfg:

                cls.uniformDHSecret = base64.b32decode(util.sanitiseBase32(

                        cfg["password"]))

                cls.uniformDHSecret = cls.uniformDHSecret.strip()



    @classmethod

    def get_public_server_options( cls, transportOptions ):

        """

        Generate and return a password if it's not in Tor's torrc.



        This method implements a fallback mechanism if the bridge operator did

        not specify `ServerTransportOptions'.  In that case, we silently

        generate and store a password.

        """



        log.debug("Tor's transport options: %s" % str(transportOptions))



        if not "password" in transportOptions:

            log.info("No password found in transport options.  " \

                     "Taking care of that.")



            # First, try to load the password from file.

            rawPassword = util.readFromFile(const.STATE_LOCATION +

                                            const.SERVER_PASSWORD_FILE)

            if rawPassword:

                password = yaml.safe_load(rawPassword)

                log.debug("Loaded password from file.")

            else:

                # ...if that fails, generate a new one and store it.

                log.debug("Generating new password and storing it in `%s'." %

                          (const.STATE_LOCATION + const.SERVER_PASSWORD_FILE))



                password = mycrypto.strongRandom(const.SHARED_SECRET_LENGTH)

                util.writeToFile(yaml.dump(password), const.STATE_LOCATION +

                                 const.SERVER_PASSWORD_FILE)



            transportOptions = {"password": base64.b32encode(password)}

            cls.uniformDHSecret = password



        return transportOptions



    def deriveSecrets( self, masterKey ):

        """

        Derive various session keys from the given `masterKey'.