In this lesson, students deepen their understanding of encryption by exploring how a different method of substitution can be used to transform information. Building on their prior knowledge of ciphers and access control, students first use a telephone keypad to analyze and decode a message encrypted using a polyphonic cipher. They then use the polyphonic cipher to encrypt their own secret message, and assemble a Scratch program that checks a user’s input for the correct encryption. Finally, students share their programs with their peers to receive feedback about their programming decisions.