The CryptoClub Cipher Handbook is recommended for use in informal learning environments such as afterschool and enrichment programs. It teaches cryptography as an application of mathematics topics from the middle-grade curriculum. It covers six ciphers: Caesar, additive, keyword, multiplicative, affine, and Vigenère. The mathematics involved includes negative numbers, decimals, percents, prime numbers, common factors, inverses, methods for solving linear equations, division with remainder, and pattern recognition. Overarching themes throughout the book are problem solving and reasoning. The