The Codebreakers - The Comprehensive History of Secret Communication from Ancient Times to the Internet

"Few false ideas have more firmly gripped the minds of so many intelligent men than the one that, if they just tried, they could invent a cipher that no one could break," writes David Kahn in this massive (almost 1,200 pages) volume. Most of The Codebreakers focuses on the 20th century, especially World War II. But its reach is long. Kahn traces cryptology's origins to the advent of writing. It seems that as soon as people learned how to record their thoughts, they tried to figure out ways of keeping them hidden. Kahn covers everything from the theory of ciphering to the search for "messages" from outer space. He concludes with a few thoughts about encryption on the Internet.

The Washington Post Kahn has produced a tour de force...The volume is an anthology of a hundred detective stories, one more ingenious than the last, and all real, central to the fate of armies and kingdoms....Magnificent.

The Christian Science Monitor A literary blockbuster...for many evening of gripping reading, no better choice can be made than this book.

Time Perhaps the best and most complete account of cryptography yet published.

The New York Times Book Review A notable achievement...Mr. Kahn has presented the specialist and the general public with a lavishly comprehensive introduction to a subject of basic significance for both.

Prepublication National Security Agency Evaluation, now declassified The book in its entirelty constitutes the most publicly revealing picture that has ever been presented of U.S. Sigint activities and the agencies engaged in this field.

This book is not intended to teach the reader how to design or cryptanalyze codes and ciphers; it is a history book, and a really great one. However, the reader should be aware of a couple of things that may not be apparent.
First, the 1996 "revised edition" differs from the 1967 first edition only in the addition of a final chapter to cover what Kahn didn't know (or didn't choose to include) in the 1967 edition. The first 26 of 27 chapters, and the references and bibliography associated with them, are essentially identical to those of the 1967 edition. This means that a number of statements and passages in the first 26 chapters, although correct in 1967, are misleading if one assumes they were written in 1996. I recommend that the reader skim Chapter 27 quickly before reading the rest of the book, so as not to misunderstand any of what's in earlier chapters.
Second, keep in mind that in 1967 Kahn was essentially an outsider so far as the intelligence community was concerned, but by 1996 he was definitely regarded as an insider. Hence, the new final chapter is written with complete respect for the sensitivities of the intelligence community, which the original book was not. I was surprised to see one particular statement in the last chapter until I realized that NSA wants to correct a misapprehension widely held outside the community. Much more important, Kahn now knows a great deal that he has chosen to omit from the last chapter, including much that's unclassified but still regarded by somebody as sensitive for one reason or another. He even omits certain material that he made publicly available some years ago in his written testimony to a Congressional subcommittee. So the reader should understand that this book says less than it might about various aspects of the history of cryptology and its impact dating back as far as World War II. Whether this is good or bad depends on where one sits; if one is concerned about the sensitivities of various governments, it's good; if one wants to know as much as one can about the history of cryptology since 1940 that's not still clasified, it's bad.

I first came across "The Codebreakers" in the original edition, published in the 1960s. It was a massive read, and one which I never finished in one sitting; however, a love of history, the romance of espionage and the fascination of working with mysterious information kept me going. It is a pleasure to see the book has been reissued.
Kahn does not create a textbook for the serious cryptologist; such a work would be more mathematical in approach. What he does is give, from a layman's view, a good mid-level history of the art/science of cryptology. The first chapter, covering the cryptanalytic events of Pearl Harbor, brings you in; then he goes over the history of secret writing from the days of Egyptian hieroglyphics to roughly the present day. Interesting areas include the discussion of the European "black chambers" of the 1600s and 1700s, a good talk about how rumrunners in the Prohibition days used complex code/cipher combinations to thwart the Noble Experiment, and a highly entertaining chapter on the "ciphers" that proved Francis Bacon wrote Shakespeare's works.
The updated edition falls short in its attempt at updating, which is why I don't give another star to the book. The discussion of cryptography in the world of the Internet is far too thin to satisfy. This, of course, could be a function of the beast; the Internet and electronic cryptology changes faster than any book could keep up with. In addition, information on the Enigma and other areas of World War II cryptology, declassified since the previous edition, could have been added to increase understanding of this critical time. However, the remaining "classic" text is still excellent, and has served as the layman's reference on cryptologic history for thirty years.