Diffie-Hellman Key Exchange

How do two strangers agree on a secret while everyone is listening? Art of the Problem answers with paint. Each side mixes a private color into a shared public one, swaps the result, and adds its own color again, ending with the same shade that an eavesdropper cannot unmix. The video then explains the math the paint stands in for, which lands far more gently once you already hold the picture. It also tells the story of how public key cryptography came about, and the whole thing runs under nine minutes.