Abstract
This activity is designed to cement the basics of public/private key cryptography for under-graduate students. The basics being taught are: the role of the public key and the private key; the operations of encryption and signing; the possibility of a "man-in-the-middle" attack. The class is structured as an adversarial game between two teams trying to exchange messages and a third team trying to intercept that message. The class was conducted with large paper props representing messages, keys and the operations of signing/encryption. The adversarial (but friendly) nature of the game encourages students to better understand the situation and reason about what opportunities and problems occur for each role.