The Code Book

The Secret History of Codes and Code-Breaking

By Singh, Simon
1999, Fourth Estate
ISBN 1857028899
Paperback, 416 pages, many diagrams and photos.

Descripton: A superb book on the history of cryptography (including, of course, the Enigma machine), from the ancient Greeks right up to the modern alphabet soup: RSA, DES, PGP. Excellent explanations of all the above codes and how they work, with examples. Very very readable despite the technical stuff, the most technical of which is separated into the various appendices.