My laptop has a USB keyboard (well, that's how it's presented, wiring is all internal), and I regularly connect an external USB keyboard to it. You might think

My laptop has a USB keyboard (well, that's how it's presented, wiring is all internal), and I regularly connect an external USB keyboard to it. You might think you could identify it by manufacturer/model (VID/PID) or even serial number, but all those are easily modifiable by a serious attacker for a given target. It might make shotgun/blind attacks harder, but ultimately it wouldnt' be much more secure than MAC filtering on your network router. There are also plenty of non-keyboard HID types that could potentially generate unwanted input of this sort, although not quite as easily.