It seems I was the only one not to know about something that requires a gigantic effort in self-discipline to restrain the geeky part of me from drooling all over the keyboard: port knocking.

Now, what is port knocking, in case you missed the train just like I did?

As Martin Krzywinski himself puts it, port knocking is a method of establishing a connection to a networked computer that has no open ports.
Before a connection is established, ports are opened using a port knock sequence, which is a series of connection attempts to closed ports.