The Code Book


Simon Singh


Non Fiction


Date Reviewed:

April 25, 2006

he Code Book is a prime example of how fascinating non-fiction books can be. This book is the history of cryptography, and it is chock full of tidbits of historical events, plus clear explanations of the ciphers work, and how the code breakers crack them. The details are so intriguing that you can't help but relate a tale or two from this book to a friend or relative; I would wager that this book is lent to others for reading much more often than most other books. Indeed, it was a friend at work who loaned me his copy. I read it in a week. Melanie saw me reading it, and she picked it up when I was finished, and read the whole book too.

The first chapter in the book deals with Mary Queen of Scots, who was plotting against her relative, Queen Elizabeth of England. Mary is in prison, but communicates with loyal supporters via a sophisticated code. The English spymaster must break that code so he can present evidence to Queen Elizabeth that Queen Mary must be executed. I was impressed by the sophistication of the code, which is shown in figure 8 of the book. There is a unique symbol for each letter of the alphabet, plus four extra symbols that are fakes. There is a symbol for double letters (like the "ee" in tree), plus there are unique symbols for approximately 30 of the most common words used in messages. What impressed me is that we know so much about these long ago events. Indeed, in figure 9, there is an example of one of the actual coded messages, which includes a postscript that was added by an English forger. (The English did indeed crack the code, and added their own note to an intercepted message, saying that the plotters need to send back to Queen Mary their names so that she knows who is trying to rescue her.) Singh gives us an explanation of the statistical analysis (basically, the letter e is the most commonly used letter in the English language, so substitute e for the symbol that appears most frequently, and see what further clues can be learned from the result.) and shows how early code breaking working.

The second chapter describes the next advances in cryptography, designed to defeat frequency analysis. Instead of using a single set of substitutions, substituting one character for another, messages were encrypted using 4,5 or more alphabets. This defeats simple frequency analysis, since the letter e might be encrypted as the letter x in the first alphabet, but as the letter p in the next alphabet.

There are many interesting stories throughout the book, such as the mystery of the Beale treasure, the background story of the Zimmerman telegram which propelled the US into World War 1, and of course a whole chapter devoted to the cracking of the Nazi's infamous Enigma machine in World War 2. There is also some material about reading Egyptian hieroglyphics (which weren't encrypted, but no one in the world could read them) and an ancient text called Linear B.

I have heard about public keys, but until reading this book, I didn't understand how the concept worked. How can you encrypt anything if you make the key public? Singh gives an excellent write up. The gist of the idea is that making a key public allows anyone to encrypt a message, but then no one can decipher the message unless they possess knowledge of the prime numbers that were used to generate the key. Thus, a user will publish his/her key, and anyone who wishes to send that person a message will use it to encrypt their secret. The message is then sent, and even if it is intercepted, it can not be cracked. This is the idea behind Pretty Good Privacy, which is a publically available program that allows anyone to conceal their messages. Not even the NSA can crack it (Of course, no one knows for sure the capabilities of the NSA, but it is presently believed that they can not crack PGP.)

The last chapter of the book deals with a bizarre topic called quantum cryptography, and it is a tribute to the clarity of Singh's writing that such a strange subject seems comprehensible in the book. Basically, quantum mechanics are utilized to encrypt a message, which can NOT be deciphered, not even by the NSA, at least, not unless the laws of physics turn out to be different than we currently understand. Even better, quantum cryptography will let you detect if someone has tampered with the message. I can't even begin to explain these ideas here. I highly recommend this book. It is some great non fiction writing! A lot of the subjects raised in this book sound intriguing, I will have to look up some books on Mary, Queen of Scots, Navaho Windtalkers, Enigma Code Breaking, and the Zimmerman Telegram (any book by Barbara Tuchman has got to be good).