Ciphers and Codebreaking (mini booklet)

Originally written for Algebra 2 students as a fun end-of-year after-testing activity. It's a lighthearted take on the subject but includes some more serious math.

This is a 58-page mini-textbook that covers some basic elements of classical cryptography, including Caesar, vigenere, affine, and keyword ciphers, among others. It discusses modular arithmetic, solving algebraic equations with modular arithmetic, and some basic work with prime numbers (coprimes, Ulam's spiral, Mersenne Primes).

The book includes a link to a companion website which will allow students to see a specific decryption algorithm at work and test it themselves. The book also includes approximately 10 practice ciphers to attempt decoding. Finally, there is a page that can be cut-out and assembled into a cipher-wheel as a physical manipulative.

WARNING:

The book is downloadable as a microsoft word file. You MUST print with the selection "print on both sides - flip pages on short edge" or the pages will not line up correctly. Specifically, pages 9-10 are intended to be torn out and used, so unless you select the correct printer option these will not line up correctly.

Once printed, the book folds into five signatures of three sheets for 12 "pages" in each signature.