Codes and Ciphers
Clever Devices for Coding and Decoding to Cut Out and Make
Make this collection of seven ingenious paper gadgets which introduce and explain many of the concepts used in cipher machines.
Decode the secret messages and then start to understand how cryptographers try to protect information from prying eyes.
See also how cryptanalysts set about breaking such codes and ciphers.
A substantial minibook explains the principles of codebreaking, and includes the story of the Enigma machine and Bletchley Park.