I have a small network of servers and I would like to increase the general security. I don't have enough time/money/paranoia to set up a VPN -- what's a basic way I can increase the security of my system?
One thing could be to require that users both send their key and enter a password. This is kinda hard to google for because everything about "ssh key password" is about sshing without a password. :-)
One scheme I've always wanted to toy with is requiring that incoming connections only come from a whitelist of dyndns ip addresses. I know some security heads would vomit at the thought of the idea, but the fact of the matter is it would add very significant complexity to exploit a box.
What do you think? What else is out there?