The Security Protocol Game is a highly visual and interactive game for teaching secure data communication protocols. Students use the game to simulate protocols and explore possible attacks against them. The power of the game lies in the representation of secret and public key cryptography. Specifically, the game provides representations for plain text and encrypted messages, message digests, digital signatures and cryptographic keys. Using these representations, students can construct public key certificates and perform multiple encryption, tunnelling and encrypted key transmission. They can simulate a wide range of protocols including authentication, key exchange and blind signature protocols. Application protocols such as Transport Layer Security and Pretty Good Privacy can be simulated in detail. The game clearly reveals the key issues of confidentiality, integrity, authentication and non-repudiation in secure data communications. Used as a small group learning activity, students gain a deep understanding of protocol design and operation issues. The game is suitable for use in tertiary and professional education courses for managers and information technology students at all levels.