The Code Breakers David Kahn

The magnificent, unrivaled history of codes and ciphers--how they're made, how they're broken, and the many and fascinating roles they've played since the dawn of civilization in war, business, diplomacy, and espionage--updated with a new chapter on computer cryptography and the Ultra secret. Man has created codes to keep secrets and has broken codes to learn those secrets since the time of the Pharaohs.