I enjoyed the Triumph of the Nerds very much and also this book. Just as Cringely had, the author possesses a fine pedagogic instinct for technical matters, and definitely understands how to "herd" the crowd. He has made interesting a topic that may have been too technical for lay readers. I was so enthralled by this book at my time of reading that upon finishing it I immediately went out to purchase his other book, "Fermat's Last Theorem" (Singh's formula didn't quite work there, perhaps because there weren't enough contemporary parties to throw interviews at -- thus losing the dynamism present in this book -- but that's a different story).
This much said, a word of caution. This is after all a pop science book, light reading. It is difficult to imagine how a chapter about public key cryptography can be written without mentioning certificate authorities or hashing, but here is one.
Sit back, relax, and enjoy. This may very well be the pop science book of the decade.
The strength of Singh's book is its readability and structure. He introduces various methods of encoding information, points out the weaknesses that were exploited to break the code, then how the cryptographers came up with a new code to foil the codebreakers. Singh especially stresses the practicality of each method - there are very simple encoding schemes that are actually unbreakable, but also completely impractical for everyday use. This is especially important to the military - what good is a battlefield code if it takes too long to decode?
Early chapters are of historical interest, but also contain codes and ciphers that are very easy to understand, so the reader gets comfortable with the language and problems of cryptography. Each chapter presents a more complex cipher than the previous, and each time Singh explains it easily, even such convoluted automations as the Nazi Enigma machine. He offers some fascinating diversions into ancient language elucidation (e.g., heiroglyphics), and eventually ends with a discussion of quantum computers and quantum cryptography. This is an area especially challenging to explain to the lay reader - based on the other reviews, he has done well. This section is clear and fascinating to read. As a chemist familiar with quantum mechanics, I can assure you that the scientific facts are presented accurately, much to the author's credit.
Therefore, I highly recommend this book as an insightful, educational, and enjoyable introduction to cryptography. You will learn a lot, and will enjoy learning it.
Singh also provides easy to understand ways on how encryption works and even more intriguing, how to break it. He shows how all various encryption algorithms are done, and then how code breakers can decipher them, both in practical and historical consequences.
In the end, he even provides a challenge for would be decipherers out there. Granted, it's already been solved, it's still education and exciting that he offered a considerable amount of money for this challenge....
All in all, it's a fascinating book that will capture anyone's imagination, even if they hate history or math.