The Proof Puzzle

The arcade pays one thousand zatoshis when the safe opens, and nothing if it does not. You set a secret three-digit code inside the safe while the Watcher closes his eyes. Then he asks the safe three questions about your code. You answer yes or no. The safe checks each answer against the code inside it and only says open or shut. If all three match, the payment moves. The Watcher never sees the code.

What it teaches

Before the network accepts a payment, it checks that the money is real, that it has not been spent before, and that it is going where it says. It checks all three without showing who paid, who got paid, or how much. The check runs on math built from the secret itself, so nobody has to hold the secret to verify it. That math has a name: a zero-knowledge proof. It is the only thing the network ever sees. That is how Zcash keeps payments private while the network still agrees they are valid.

What you will see

A safe with your secret code, three yes-or-no questions, and a receipt that shows only that a payment happened.