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The Code Book
Perhaps the most remarkable thing about Simon Singh's masterful The Code Book becomes clear at the end, when he provides seven coded messages. He starts with a simple substitution cypher and ends with what appears to be a form of public key encyrption. After only 350 pages, he has made codebreaking so exciting, so worthy an endeaver, and has explained the mechanics of the process so well, that you can't help but pick up a pencil and set to work.
When compared to other mass-market books on cryptography, Singh goes into much more detail on the contruction of cyphers, and the mathematics behind them. This makes the power and momentum of his writing a bit of a surprise. However, his thrill at the cracking of each code, and his understanding of the world-altering effects of each one, infect the reader.
The book contains everything you would expect -- Vigniere cyphers, the cracking of Enigma, a brief history of public key encryption. It also includes the Beale Treasure (crack a code, and there may still be millions in gold left to find), the Zimmerman telegram (which, when decoded by the British in 1917, drove the United States to declare war on Germany), and other stories of varying levels of familiarity. Most unusual, Singh includes the story of the decoding of Linear B and Egyptian Hieroglyphics. In other books, these chapters might seem very much out of place, as neither language was developed as a tool to keep things secret, and they are therefore distinctly out of place when next to commercial and military cyphers. That said, Singh's book is more about the thrill of decypherment and the intellect of code-breakers. Since the skills necessary to decode these languages closely resemble those of code-breakers, and since the triumph of victory is very much the same, they fit here.
What's Bad?
Codes and cyphers of importance in Britain and the United States dominate the book. There is almost no discussion of codes or codebreaking elsewhere. Perhaps Singh will address them in a later book. Also, for some, very sophisticated readers, much of the math will be overly simplistic. For some, very slow readers, later chapters will be difficult to follow. However, most people will find this book to be a treasure -- worth reading, and worth sharing with others.
What's Good?
From the perspective of the early 21st century, the weaknesses of old codes are obvious. As Singh walks us through the Cipher of Mary Queen of Scots, substitution codes and cyphers of increasing sophistication, the Vigniere cipher, we cover thousands of years worth of the science of secret writing. Today, computers bring us such tremendously powerful tools for cracking these codes, that you want to put a hand over your eyes and shake your head in embarassment for the governments, businesses, and hobbyists who should have known better. When Singh shows us the first Arabic document on the use of frequency analysis to crack substitution cyphers, I felt a pride similar to that I feel when I contemplate powered flight. As Singh's story progresses, it becomes clear that the advance of code-making, just like the advance in agriculture or the advance of transportation, carries within it the evolution of global civilizations. It includes technology, politics, trade, and the the demand for civil liberties (or privacy, which often amounts to the same thing).
Singh considers future technologies as well, especially quantum computing and its implications for modern, prime-number based encryption systems. He ends with quantum cryptography, perhaps the next paradigm in secrecy. If Singh is right, there is no principal in physics as we now understand it which will allow an untrusted party to decode messages encrypted with quantum cryptography.
He has also put up $15,000 for whoever can read the secret messages at the back of the book. The first few are easy, but they quickly get difficult. If the last few are what I think they are, a distributed computing network will be needed to crack them. Anybody volunteering to organize it?
Stern is the president of Information Markets Corp. You can purchase this book at ThinkGeek.
You've indicated that you want a book that is "fun to read" and this in my mind leaves only one choice: Applied Cryptography 2nd Ed by B.Schneier. It's funny, well written, insightful and accessible.
Something like Handbook of Applied Cryptography is more precise and scientific in approach, but has 0% humour.
Seriously, buy Applied Crypto...You won't regret it. Secrets & Lies is Schneiers follow-up and this is also a very good book, but is more into dealing with computer security rather than crypto.
"Mary had a crypto key, she kept it in escrow, and everything that Mary said, the Feds were sure to know."
Get a real book on crypto (Koblitz, maybe) if you're interested in learning the math for real. If you just want a good history of the field and what it evolved from, then this is the book to get. Anybody who is interested in cryto should consider this a must-read simply for the historical perspective.
BTW, I know what the encrypted message really is at the end of the book. It's just xyzzy over and over and over......
Actually, the GCHQ is really the precursor to the NSA, and as such we don't give credit to such organiziations. We don't care how far ahead of the public world the NSA is, because we don't like them.
What's bad: Codes and cyphers of importance in Britain and the United States dominate the book. There is almost no discussion of codes or codebreaking elsewhere.
True, but the Code Book doesn't claim to be a comprehensive treatment of cryptography through the ages and around the world...And for good reason: David Kahns The CodeBreakers is the definitive comprehensive and technically rich reference of cryptography in a historical context. My understanding is that The Code Book was supposed to be easy to read and accessible (like Dr Singhs other book "Fermats Last Theorem").
Personally I believe Singh achieves this - the book is very well written and "just at the right level" for a non-technical person to understand.
"Mary had a crypto key, she kept it in escrow, and everything that Mary said, the Feds were sure to know."
I especially enjoyed hearing his story about RSA bashing (in a "polite way") on Elliptic Curve crypto. He showed us a quote by Rivest where he said that finding a mathematician who could give you a reasonable analysis of EC crypto was about as hard as finding someone to give you an interpretation of Chaldean poetry. In response, the organizers of an EC workshop that Koblitz attended had shirts made with elliptic curves on them and the statement "I Love Chaldean Poetry" silkscreened on the front.
Koblitz wore the shirt to the talk, and we all had a good chuckle. :)
I don't think that this is unusual. The landmark book for the history of cryptography, David Kahn's The Codebreakers, also contains a chapter on Linear B and the Rosetta stone. Decoding unknown languages is a good, lucid way to demonstrate how cryptanalysis proceeds without a lot of mathematics, and has the advantage of having all of the details openly published. For the casual reader without a strong background in computers or cryptography, showing how linquists decipher an unknown written language is the best way I can think of to show the thought processes of a cryptanalyst.