Can you solve it? The crazy maths of crypto
"You work in an office of 100 people. One day your favorite paper clip is stolen. You have a pretty good idea of who did it. Your colleague Annabel tells you that she also has a pretty good idea.
You want to check with Annabel that you both suspect the same person, but neither of you are willing to identify your suspect just in case you are thinking of different people. (Because of office politics, no one wants to point fingers.)
Think of a method that allows you and Annabel to check whether your suspect and her suspect are the same person, without either of you revealing any information about your suspects."
Read more about the concept of zero-knowledge proof and check your answer at The Guardian.