* This tunnel should be used inside an encrypted tunnel
* For example:

        ss-local (rc4)

          -> neko-obfs -> ss-tunnel (aes-256-cfb)

            -> gfw -> internet

          -> ss-tunnel (aes-256-cfb) -> neko-obfs 

        -> ss-server (rc4)
* Note it's the `ss-tunnel` layer that protects the obfuscation, otherwise
  data and noise length are clearly visable.