THE SECRET AGENT TRAINING MANUAL

Simple directions for using codes, ciphers, and steganography to send secret messages to friends or fellow spies.

After opening with an overview of historical cryptography from the “Caesar cipher” and an ancient Chinese script called Nushu (used exclusively by women) to the Enigma machine and other World War II–era coding devices, Hunt proceeds to describe over two dozen ways to hide or disguise messages. Along with substitution codes, letter and number grids, anagrams, a tic-tac-toe cipher, a Vigenère table, and like techniques, she provides recipes for invisible ink, instructions for creating paper decoder bracelets or rings, and templates to copy for an Alberti cipher wheel. Most of the illustrations are charts or simple line drawings, with a sprinkling of human figures (all seem to be white). The author adds frequent practice pages with blank lines and short secret messages to decode, and she closes with a series of longer puzzles (answer key included) in a final “Cryptographic Challenge.” But young would-be coders hoping to find more than passing nods to computer programs or cellphone tools—or even that much about modern advances in cryptography—will be disappointed.

A reasonably comprehensive handbook, though it’s confined to classical low- to no-tech methods.