# Unsolved!

Can you imagine: a book on cryptography that gets you hooked and keeps you reading like you would read a Dan Brown page turner. This is what Craig Bauer achieved with this book. When I had to imagine what a (popular) book about cryptography would look like, I would think about some modulo calculus, the Caesar code, perhaps something about Alan Turing and the Enigma machine, and principles of RSA and public key methods. Well, all of this is here, but it is also Indiana Jones, James Bond, The Name of the Rose, Dan Brown, the X-files, Sherlock Holmes, NCIS and Criminal Minds. You name it. Even though you already know in advance that in the end the problem will remain *Unsolved!*, you keep on reading, running along the cryptographer who is trying to unravel the mystery, collecting more and more information, trying yet another attack, following a new lead.

In fact, it gave me a complete new idea about cryptography. I would spontaneously think of it as a tool that was used to communicate a message such that the "enemy" would not be able to read it, like in war situations or when I communicate with my bank about transferring money. However, any message, in any form (text, picture, audio, or a signal from outer space, whatever, even the result of an ordinary experiment or a simulation) contains a message that we need to read and interpret correctly, even though we are not "the enemy". Sometimes this message is accidentally hidden. Usually then cryptography will not be of much help. The more challenging ones are of course the messages that have been deliberately obscured not by steganography but by following certain cryptographic rules. Of course, this is cryptography in a narrow sense where the cryptographer comes in with his or her wit and techniques (often statistical) to decipher the seemingly nonsense message. This is from all ages and all cultures and it has been a constant chase of the encryptor trying to outwit the attacking cryptographer.

In the early techniques not much mathematics was going on in the encryption process, just several methods of substituting letters or groups of letters or words by others or replacing them by especially designed symbols. Statistical techniques, using the frequencies of letters or groups appearing in some language may help detect what kind of substitution is used. It then remains to try to discover some key which requires wit and guesswork. Usually some modulo calculus, perhaps transposing a rectangular table, or transforming letters in numbers which are submitted to simple numerical transformations before transforming back to letters. But that is about all the mathematics that are needed, until prime number factorization becomes essential in RSA type methods. RSA is explained but it comes only at the very end of this book. This means that a mathematical education is not needed to read it. Nevertheless cryptography is usually considered as part of mathematics or maybe computer science or electrical engineering and it are often mathematicians and the likes who seem to have a knack for cryptography.

Rather than explaining different cryptographic methods and how to attack them and illustrate these with some examples, Bauer had the marvellous idea of presenting (historical) cases of ciphers which, at the time of writing of the book, have not been solved. This does not mean that they will not be solved in the future. Too often a code was assumed to be unbreakable in the past and yet it was eventually solved, certainly since computers could be employed to test a zillion of possible alternatives. The subtitle says it all: *The History and Mystery of the World's Greatest Ciphers from Ancient Egypt to Online Secret Societies*. Bauer has the gift of presenting the cases in such a way that you, as a reader, are confronted with a puzzling problem and you are fed with little teaspoons uncovering more information and background and along the way you are also instructed about the method of encryption and the way to attack it. It keeps you on the tip of your chair eager to read on. Obviously all these real life puzzles presented involve some cryptogram and it will turn out in the end that it could not be solved until now.

For some of the cases we do not know the origin of the cipher, and hence we cannot be absolutely sure that it is not a hoax. For others, we do know who produced it, challenging whoever wanting to know the content. I did not expect that there were so many weirdos trying to communicate with deceased or claiming they will try to get a message across after they die. These are relatively harmless but much more frightening are the serial killers hiding their identity in a cryptogram, claiming yet another murder on their list. Among the manuscripts with unknown origin we read about the much investigated Voynich manuscript from the early 15th century. But there are also Egyptian hieroglyph inscriptions and cryptic Viking rune stones. It helps if we know something about the author of the cryptic message. For example the Dorabella cipher which is a cryptographic letter by Edgar Elnar mailed to Dora Penny. Nevertheless this one could not be decrypted. The Zodiac is a serial killer who committed several murders around 1970 in the California Bay Area identifying himself with cryptic messages. He stands as an example for other similar cases. The Somerton man was found poisoned in Somerton Australia. While trying to identify him, also some cryptogram was involved. The most challenging ciphers come of course from cryptographers. An example is the *Krypton* sculpture, a piece of art by Jim Sanborn, placed in front of the CIA headquarters in Langley. It has 4 parts with cryptographic texts. The first three have been solved, but the last one is still open. There are treasure hunting cryptographic puzzles (online or not) hiding the identity of the author or the location or nature of the eventual treasure. And there are messages to or from outer space and many more unsolved problems, too many to enumerate them all. As I already mentioned at the end of the book RSA encoding is explained.

If you have read my review this far, it will be clear that I am blown away by this book. I have never read a non-fiction book before that is so thrillingly entertaining and forces you to read on nearly holding your breath. You are left in awe reading the details of what murderous weirdos are capable of, your curiosity is tickled to the extreme trying to find out the meaning of a strange manuscript, and you are left in admiration for the ingenuity of the cryptographers, and in the latter Bauer has contributed his part. Even though this is a thick book, it could not contain everything. Much material is available on the web and Bauer refers to it in the text and points to the many references to be consulted for further documentation. The last paragraph is entitled "More to Come!". I am already hoping now that there will be more of the same in the future.

**Submitted by Adhemar Bultheel |

**28 / Jun / 2017