'Do the obfs3 handshake:
PUBKEY | WR(PADLEN)'

def circuitConnected(self):

    padding_length = random.randint(0, (MAX_PADDING / 2))
    handshake_message = (self.dh.get_public() + rand.random_bytes(padding_length))
    self.circuit.downstream.write(handshake_message)
