The Code Book, by Simon Singh

"The Science of secrecy from ancient Egypt to Quantum Cryptography"

Quite an interesting non-fiction book, this book goes through the history of codes and hiding information. How we used to do it, how we do it now, how it will be done, and how we break it. It explains how information is encrypted today. It can be had off of amazon for about $14, so if you're interested in this kind of stuff, I recommend it