Tough problem for sure, especially getting users to understand. For keyboards you could use the Bluetooth pairing trust trick. Display a short random number cod

Tough problem for sure, especially getting users to understand. For keyboards you could use the Bluetooth pairing trust trick. Display a short random number code on the screen, and only accept the keyboard if the numbers are typed, which could be interpreted as the user vouching for the keyboard. The need for this in Bluetooth land is more obvious due to the wireless nature of it, but USB is also an untrusted network.