Writing and breaking codes is an essential skill for any secret agent and great fun for everyone else. Expert Herbie Brennan's guide tells you everything a cryptographer or code-buster needs to know: how to crack codes, tools to hide messages - from invisible ink to computer pixels, how to develop complex ciphers, exciting code-busting events from the Kama Sutra to the Enigma machine and computer ciphers, and allows you to test your skills with code examples and tests.