While I am not at all a fan of the “security through obscurity” paradigm, I think in some cases it has its benefits. For example in preventing automated scripts (i.e., worms) to compromise your box. I found this page about “Port Knocking” which only opens port 22 if you connect to a series of other ports beforehand. What I like about this solution is the simplicity by using iptables.
The solution uses the
-m recent –rcheck
feature of iptables to open port 22 if a certain other port is being connected to.