The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography by Simon Singh

An intelligent mix of history and how-to

In The Code Book, British author and physicist Simon Singh provides a history of cryptography from ancient times to the present. This is a popular science book aimed at general readers, so the text is accessible and isn’t bogged down with incomprehensible mathematical jargon. It’s still an intellectually challenging read, however, and those who are interested in the arcane details of this subject will find it quite entertaining. Singh explains that The Code Book is really more about ciphers than about codes, but The Cipher Book just wouldn’t sound as cool.

Every time someone writes a book about cryptography for the general reader, some fundamentals must be covered. First of all, the author must explain how a simple alphabetic substitution cipher works (each letter in the alphabet is substituted for another). Then, the writer must explain how to solve such a cipher using frequency analysis (the most commonly used letter in the ciphertext, for example, is likely to represent E, the most common letter in the English alphabet, and so on). Anyone with an interest in cryptography already knows about these elementary matters, but they must be included in order to lay the foundation for the discussion and to educate newcomers to the subject. It’s no small feat that Singh manages to explain these basics in an articulate way that novices can understand but won’t bore the pants off those who already know what he’s talking about.

The Code Book is a fascinating mix of cryptographic history and practical knowledge on how ciphers are created and cracked. Singh doesn’t just talk about how ciphers were used in the past and show you some examples. He really gives you an understanding of how each cipher works and the motivation behind its development. There’s an entire chapter, for example, on the Nazis’ World War II code machine named Enigma. The reader comes away with a pretty thorough understanding of that mechanism’s cryptographic process. This is followed by another chapter about how the Allies cracked the Enigma cipher. From there, Singh goes into digital cryptography. To some extent, computer-generated ciphers are too complex for the unaided human mind to unravel, but Singh still does a great job of explaining the methods and mathematics behind today’s digital encryption. Finally, Singh moves into quantum cryptography and quantum computing. In order to discuss these topics, he has to give the reader a nutshell overview of quantum mechanics, which he manages to do quite eloquently.

Singh goes off on some digressions that feel unnecessary. In the first chapter, I don’t think I needed a complete biography of Mary Queen of Scots to figure out how her cipher worked, and the discussion of cryptography really got lost amid all the historical context. Singh also spends half a chapter on the decipherment of ancient languages, such as Egyptian hieroglyphics and Linear B. While I’m interested in that subject, it feels out of place here because it ventures more into linguistics than cryptography.

The Code Book was published in 1999, so it only covers the history of cryptography up to that point. A lot has happened since then. Singh writes about identity theft and personal data leaks as if they were events bound to happen in the future, not the common occurrences of today. Although he covers the initial scientific investigations into quantum computing, further developments have occurred in the past two decades. This is a history book, after all, and the present never stays the present forever. As a historical summary of cryptography up to the year 2000, it’s hard to imagine a better one-volume treatment than this.  

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