You are standing outside of a sealed room (you cannot see inside it in any way). There are three light switches on the wall, one of which controls a light bulb inside the room. Explain how you would manipulate the switches to determine which one controls the bulb. You are only allowed to enter the room one time. How can you solve the problem? What assumptions do you need to make. Consider thinking "outside the box".

As soon as you discover that you cannot solve the problem using just the switches and the results, one needs to look for a way to get additional information.

In particular, one binary (yes-no) decision is not sufficient. Two binary (yes-no) decisions are needed so a way to find additional information is needed.

In the security field, this additional information is called a side channel. Side channels can be used to break the security of systems but need to be accounted for when protecting systems from compromise.