Simon Singh
Books: History | Mathematics | Cryptology
The Code Book (1999)
A history if cryptology and cryptanalysis. This is an absolutely fascinating book, looking at the earliest instances of cryptology and hidden messages, to the political and social ramifications of secret messages, and quantum cryptology (although I have to admit that I skipped the section on quantum cryptography).
He describes how cryptology works and adds stories of how cryptology has affected politics and the the world in which we live. His technical details of how the various cryptographic processes work are excellent, as is his description of both the German's Enigma machine of WWII (including pictures), and modern computer cryptology, including PGP or Pretty Good Privacy, the computer security software available free to home users.
He also talks about how the first true computers were created by British cryptanalysts but the information was classified for years. But this is not dry technical detail; he discusses the people behind the breakthroughs, as well as, starting with the trial of Mary Queen of Scots, the effect that these discoveries had upon the world.