Correct me if I'm wrong, but I don't think iptables allows you to authenticate the knocks? Also, anyone listening to your network would be able to replay the sequence and open the port.

This project reminds me a bit of moxie's knockknock[1], where the idea of port knocking is kept intact, but with some added security. Plus, it seems really easy to setup, compared to writing dozens of iptables rules.

[1]: https://github.com/moxie0/knockknock