The 35-year-old saga of Kryptos, an enigmatic sculpture containing four encrypted messages outside the CIA headquarters, just ...

In general, you want to avoid writing down sensitive information and just keeping it in your head but that's not always an option. If you have to write down a password, or some other sensitive ...

1. Introduction -- 2. From Julius Caesar to simple substitution -- 3. Polyalphabetic systems -- 4. Jigsaw ciphers -- 5. Two-letter ciphers -- 6. Codes -- 7. Ciphers for spies -- 8. Producing random ...