The Code Book
I just finished reading The Code Book by Simon Singh. I would recommend it to anyone interested in the history of cryptography, as well as the specifics of some of the techniques. It includes historical information from Egypt to modern day. I found the sections describing the Enigma engine particularly interesting, as well as the discussion of the recent history of RSA encryption and PGP. It is an easy read; you don’t have to be a mathematician nor a computer scientist to understand it. It will also help you how your web browser does encryption, and the relationship of the certifying authorities to web based encryption.