I have a terrible, terrible secret. I want so desperately to tell it to you, but it’s important that it doesn’t fall into the wrong hands. So suppose I write it in a secret code. Of course, there’s no way I can give you the code now without giving it to everyone, so the only way you can ever find it out is to crack the code yourself. I can’t guarantee you’ll be able to do it, but if you can, then you must be someone who deserves to know it.
Codebreakers, by David Kahn (1968, reissued 1996) is an epic history of the ways people try to hide messages and how others break them. It’s the big classic of cryptography; if you’ve read anything else on the subject, chances are that author started off here.
The book follows two tracks. One is the history of cryptography itself—how the art advanced, how standard techniques developed and how some of the basic ciphers work (I should take a moment to give some definitions: steganography hides information, as in invisible ink, etc.; cryptography transforms information, as in codes and ciphers; codes are made up of words or number that substitute for other words; ciphers substitute letter by letter to more or less create a new alphabet ). There is a lot of very technical stuff here—if you’re not a math genius (and I’m not) or a math-fairly-competent (uhhh, not that either), then you might struggle with some of this. Probably the best advice I would give anyone reading this is to not go crazy trying to understand every code, and just keep going rather than labor over some of the more difficult ones (unless you’re planning a career in cryptography, in which case, if you are having trouble reading this book, welllll…maybe you ought to rethink your future). I found that was the best way to manage, though even that may occasionally leave you a little lost; a sentence like “For simplicity’s sake, this may be imagined as a St. Cyr slide with a mixed cipher alphabet that shifts forward one space after each plaintext letter is enciphered,” sent me running for the index to try to remember the difference between a St. Cyr slide and your basic Caesar slide. (I should note, I also went back later and just spent time with pen and paper working through some of the codes in isolation, without worrying about them as part of the text. That worked for me and made me feel a little better. I should also mention that I am painfully aware that I use way too many parentheses).
Much of the book shows how the history of cryptography basically shadows developments in communications. People write letters by hand, people create letter and number codes to conceal the original text; the telegraph is invented, and so are ways to encode text for that machine; radio messages are sent, radio messages are encoded, intercepted and the code broken. Photography is invented, coded messages are photographed and shrunk down to microdots. Typewriters are at the root of the Enigma machine, telephones lead to voice scramblers that hide voice conversations, and those too are broken back down again. This is all great stuff, but I was rather charmed by some of the more low-tech methods—the secret words thrown into radio broadcasts, the endless messages hidden in personal ads. These are probably the hardest to execute, but the most foolproof when done right.
The other major track of the book is the role of codes in history. Codes, it seemed, have been a part of just about every big event (this makes sense because if these were small events, no one would be interested in keeping them secret). Mary Queen of Scots and her plot to overthrow Elizabeth, the Zimmerman telegram, the Dreyfus Affair. Lots of WW I and WW II, including a minutely detailed section on the hours leading up to Pearl Harbor and the attempt to decode and understand the intercepted Japanese messages coming during that time (none of which, by the way, said “Hey! We are bombing Pearl Harbor on the morning of December 7th …”).
The book covers the development of official cryptography branches in various different nations. Some were better than others—according to Kahn, France was super, Japan not so super; Russia not so great in WW I, but Most Improved Campers in WW II. The U.S. seems to have been the only one to dissolve an enormously successful cryptography group due to moral anxiety. The American Black Chamber, established as part of the State Department towards the end of WW I, was shut down by Secretary of State Henry Stimson because he thought it was a kind of low-minded snooping that violated the trust and openness that made for good foreign policy. The newly unemployed, former head of the ABC, Herbert Osborne Yardley, responded by writing a book called The American Black Chamber that told everyone who wanted to read it exactly what they did, how they did it, and who they did it too, albeit with a somewhat melodramatic cast. Presumably this was not the kind of openness Stimson had in mind.
The general sneakiness of cryptography was not the only moral dilemma faced by cryptanalysts. What if you had worked for months, if not years, to break a code, used it to follow the moves of your enemy on a daily basis and then one day found a piece of information that could change the whole direction of a war? However, if you acted on the information you had obtained, it would become obvious to your enemy that you knew their codes, they would change them and you would have to start all over. This risk was handled in different ways. To get the information in the Zimmerman Telegram out without revealing who had cracked it, cryptanalysts rerouted it through a number of different channels before letting its contents became public. In WW II, the US got information revealing the travel plans of Admiral Yamamoto, Japanese Commander-in-Chief of the Fleet and architect of the Pearl Harbo attack. Taking out Yamamoto would have a powerful effect on Japan’s war effort, but losing the ability to read Japanese encoded messages would also hurt the US. The chance to get Yamamoto was too good pass up, though, and Japan’s lack of reaction in the past to reports that the US had their codes made it a worthwhile risk—and it worked. Yamamoto’s plane was shot down and the codes remained in place.
Kahn covers this immense wealth of information as clearly as possible, in a structure that is logical and easy to follow. He doesn’t spend a lot of time on biographies of the people involved in cryptography, though (which considering it’s a 900 something page book is probably a necessity). Most descriptions tend toward the “a tall, well-dressed soft-spoken man,” or an “outgoing, hard-living, poker-player, ever ready for the main chance” type (and that would be you, Herbert Yardley). I was most fascinated by William and Elizabeth Smith Friedman, cryptography super-couple, who met when they both were hired by an eccentric millionaire to work at the lab he had established to prove that Shakespeare’s plays were written by Francis Bacon. Along the way they got married, developed mathematical formulas that turned cryptography from an art into a science, worked for the US signal intelligence (him), worked for the Coast Guard tracking bootleggers during Prohibition (her) and finally, writing a book together that revealed the Francis Bacon thing as a whole lot of nonsense. There’s not a lot of info about either of them, but I would like to imagine them as sort of a Nick and Nora Charles of cryptography (Him: “How’s that superenciphered polyalphabetic code coming along, my darling?” Her: It would come along a lot better with some champagne. Do be a love and get me some. This beastly hangover keeps turning my Gronsfeld Square into a Vigenere Square.”).
While I am deeply impressed by this book, I do have a few problems with it. One is that the information about Morse and Morse code is totally wrong (it should be no surprise that I am complaining about that). Another is a peculiar problem with the index. When I first got the book out of the library, I went through the index looking for some of my, well, favorite cryptography people and stories. I looked for Linear B, found no listing for it, shrugged, and thought oh, how unfortunate, no Linear B here. Then towards the end of the book, what do I find? An extensive section on Linear B. So I have no idea what went wrong there (I do love the Linear B story; maybe I should write something about that here sometime).
A problem that can’t be helped is the passage of time. The book was originally written in 1968, with material added in a reissue in 1996. Note that—material was added, it wasn’t really updated. So there are some things that stand out. A reference to Germany’s seemingly inexplicable lack of action during the run-up to D-Day was, I would guess, really due to the counterintelligence work of super double-agent Garbo, which was not yet declassified when this was originally written. The Soviet Union is written about in present tense, and in another symptom of the time period, it is noted that working at NSA was a problem for girls in their early twenties, because “its compartmentalization and restriction of movement tend to limit their romantic aspirations.” Ah, yes, what is the point of a job when you don't have a chance to marry the boss? Also, some terms and descriptions are used that are very cringe-inducing, so I won't put them out here in public again.
Despite this, Codebreakers still remains an important source for anyone interested in cryptography. After reading through it all, though, what fascinated me the most is that even with all the formulas, all the machines, all the technology that went into making and breaking codes, there have always been two factors that were more important than any of that. One is a basic understanding of language itself—which letters in a language are the most frequently used, which the least; what kind of consonant vowel pairs are common and which are impossible. Knowing your enemy is also important, as in knowing what topics, and thus which words are likely to appear in a message, what kind of salutations and phrases are typically used, what names and places might be discussed. These types of things are almost always the first keys to a code; here intuition is just as, if not more important, than technology.
The other factor is human error—the code clerk who mistakenly uses the wrong code on the wrong day, doesn’t change the codes as often as instructed, or is too lazy to look up the most precise word or phrase in a code book while encoding a message. The telegraph operator who misses a dot or a dash and the person who is easily taken and gives a code book to a spy posing as a friend or lover. All the technology in the world, all the foolproof formulas and algebraic structures of codes can’t overcome this sort of thing. Which makes it all the more fun, of course.