: The Evolution of Secrecy from Mary, Queen of Scots
to Quantum Cryptography
A book written by Simon Singh. Published by Doubleday in 1999. It is about the history of secret codes, cryptography, and other methods of attempting to communicate in secrecy.
I just started reading this book. I'll add more once I finish. I watched Mr. Singh give a talk about the book on C-SPAN. It sounded interesting after having read Cryptonomicon.
Update: Wow! It was a damn good book. I highly recommend it for anybody that is interested in the history of cryptology. It is far from a complete history and it does tend to lean heavy on what the British have done. It isn't a textbook that explains all the math involved with each system, but it was much easier to read than a textbook. It tells the story of the men and women involved in some of the important steps in cryptology's development. Similar to a PBS or History Channel documentory. (Mr. Singh's day job is writting those types of shows.) It also has an excellent set of reference's for further reading in the back.
It also includes a contest, The Code Book Cipher Challenge. The first person to decrypt all 10 steps will win $15,000. More info can be found at http://www.4thestate.co.uk/cipherchallenge.