Where's Waldo?

Frederick: Where's Waldo? I'll describe what it is if people don't understand. One person that wants to prove that they found Waldo. The other needs to verify whether or not the prover is telling the truth and has actually found it. Frederick: This is a very, very basic example of a interactive zero-knowledge proof. Our next example is going to be a far more common example. We're going to call it red pill blue pill.