Bering-uClibc 6.x - User Guide - Advanced Topics - Setting Up SSH password-less login and Port Knocking
SSH (DropBear) allows password-less login by using RSA security key pairs. To set it up you will have to generate the RSA key pairs on your client machine and copy the public key in /root/.ssh/authorized_keys. If you have more client machines, repeat the same process and append the public keys in /root/.ssh/authorized_keys file.
You can now login in your firewall without a password. You could disable password login but be careful not to lock you out...
If you intend to log from the internet, you have to add the following rule to /etc/shorewall/rules
SSH(ACCEPT) net fw
You can always choose another port like 65022 for SSH to listen to. The port scanners wont usually reach there. There are going debates about the questionable security of this obfuscation... Anyway, if you do, add this rule then:
ACCEPT net fw tcp 65022
If you don't like to type ssh -p 65022 email@example.com when you login, you could also hide the default SSH port 22 with port knocking. The port is then normally closed up until you send a proper sequence of port connections, using TCP or UDP. The port knocking software will detect this sequence, and will open up port 22 for 60 seconds for instance, thus giving you time enough to make your SSH login connection attempt.
Near the end of this article: " http://shorewall.org/Events.html " you will find in Examples a simple Port Knocking setup that works quite well.