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 ...

You could do worse than to confuse the meanings of "code" and "cipher"—even cryptographers sometime use the terms as though they had the same meaning. There is, however, a definite distinction between ...

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 ...