1RSA: Building a Public Key from Secret IngredientsBuild a real RSA key pair with numbers small enough to check by hand, and see what each number does, why it works, and where it would break.Foundational 2Diffie-Hellman: Making the Same Secret Without Sending ItTwo strangers can agree on a shared secret while everyone listens. Here is how the trick works, with numbers you can check, and the one thing it cannot do.Foundational 3Elliptic Curves: Repeated Steps, Compact Public KeysElliptic-curve keys are a secret count of steps around a curve. Walk a tiny curve by hand, see why the count stays hidden, and learn which curve does which job.Foundational 4Signatures: What the Signer Computes and the Verifier ChecksA digital signature is a short calculation anyone can check but only one key can produce. Sign and verify two tiny examples by hand and see what the check really proves.Foundational 5One Agent Connection, Several Different KeysOne secure call from an AI agent to a tool quietly involves at least four kinds of keys. Follow the handshake, name each key, and see what stealing it would really cost.Foundational