2009 05 22
Recently read: The Code Book

Posted by in: Books, Cryptography

Simon Singh. The Code Book: The Evolution of Secrecy from Mary, Queen of Scots, to Quantum Cryptography

When I was seven or eight I read a kid’s book in which the protagonist is challenged by a professor/substitute-father-figure type to come up with a cipher that the professor-type can’t crack. The protagonist whips up an enciphered message and then watches in dismay as the professor-type cracks it quickly before his eyes using frequency analysis, a simple technique that uses the relative frequencies in letters in the relevant language to make educated guesses about the cipher used to encipher the original message.* (If you know what book this was, please let me know. I can’t remember.) When I was seven or eight this blew my mind and I spent many hours in the following years daydreaming about stronger methods of encryption. Indeed, even though my talents obviously don’t lie anywhere in the vicinity of this sort of problem, I still sometimes find myself idly thinking about it and related problems on the subway or while I’m walking down the street.

Thanks to Simon Singh’s entertaining The Code Book, I was recently able to relive some of my childhood enthusiasm for cyphers and cryptography. Singh reviews the history of cyphers and secret writing, from the cipher that Mary Queen of Scots trusted (unwisely) to keep the secret of her involvement in a plot to assassinate Queen Elizabeth to the enigma machine to quantum cryptography. Over eight unhurried chapters, he charts the history of the problems that cryptographers faced and the characters involved in each chapter of this history.

Singh’s willingness to digress a bit from his main theme also leads him to include a chapter not on cryptography at all, but rather on the related problem of discovering the meaning of lost languages. This was just as well, since the two episodes that Singh reviews—the decipherment of Egyptian hieroglyphics using the Rosetta Stone and the decipherment of Linear B (Mycenaean Greek)—are fun and interesting.

Readers looking for a technical, advanced discussion of cryptography might be underwhelmed by parts of Singh’s exposition, but I thought he did a great job of providing an accessible and non-technical explanation of some reasonably sophisticated ideas. There’s nothing here that would really stump a bright high school kid, and a lot that would she would find stimulating. Recommended.

* The letter ‘e,’ for example, occurs more than any other in the English language. If you’re trying to crack a monoalphabetic substitution cipher (a very simple type of cipher in which each letter in your message is swapped for a different one in the enciphered text), and you see a ton of z’s, for example, you can guess that ‘z’ encrypts ‘e’ in the cipher. If you find a letter standing alone in your enciphered text, you’re likely to be dealing with either an ‘I’ or an ‘a,’ since these occur alone in English all the time. And so on.

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