Book Review: The Code Book (1999) by Simon Singh

In this book, popular science writer Simon Singh lays out the history of cryptography. This is a considerable challenge, but Singh tackles the subject with great knowledge and ability. In eight chapters (c.350 pages) he manages to tell the story fluently and efficiently. Singh takes enough time to examine the mathematical principles behind the way that particular ciphers work, but his analysis is never so complicated that he loses the lay reader.

The stories in many of the early chapters are well known to those who already have an interest in the subject and Singh appears to rely quite heavily on The Codebreakers by David Kahn – long recognised as a key work on the history of cryptography. But Singh’s book has considerable strengths of its own. In an age of Turing-worship among certain historians, Singh correctly identifies that the Bletchley Park enterprise was very much a team effort in which electrical engineering as well as mathematical abilities played a key role. Singh is also right up to date (at least for when the book was published): he is able to reveal the triumphs of such men as James Ellis, Clifford Cocks and Malcolm Williamson. These GCHQ cryptanalysts were instrumental in breaking public key encryption – a system which was thought to be unbreakable right up until the 1990s. As with the heroes of Bletchley Park, these men were not given the recognition they deserved because they were government employees and their mathematical breakthroughs were so ahead of their time that they could not be announced for national security reasons. Singh was quite fortunate in that GCHQ did finally acknowledge the work of these men once other mathematicians had made similar breakthroughs and that he was therefore able to tell the full story.

Singh takes the story all the way up to the prospect of quantum computers and quantum analysis. His explanations of this complex topic are dense, but, if one pays attention, they are clear and thorough. Singh’s conclusion is that if quantum encryption ever becomes feasible then it is the cryptographers who will have won the ancient battle with the cryptanalysts. A truly unbreakable quantum code will one day become available – until someone discovers a new law of sub-atomic physics that is.

If Singh’s account has any weakness at all, it is that the author is a mathematician and not a spy. To be honest, spies in the field have never had a lot of time for secret codes. For a start they tend to be a pain in the neck to use. Anyone who has ever fiddled with the calculations of a “one-time pad” and its associated headaches will tell you that.

Secondly, spies don’t trust codes. Many of the operations that Singh describes (the Nazis misplaced faith in Enigma being the classic) tell of how someone assumed that the code they were using was completely unbreakable only to learn that their enemies had been reading the “secret” correspondence all along. Only recently, in 2006, MI6 officers who were using the modern electronic equivalent of the old one time pads, were caught out and exposed to public humiliation during the “Spy Rock” incident in Moscow. That says it all.

Finally, all spies know that there are alternate ways of dealing with even the toughest codes. People can be bought or otherwise persuaded to talk, cipher keys can be stolen, machines can be copied. Singh starts his book with a detailed account of the breaking of the code used by Mary, Queen of Scots in her attempt to escape from captivity as part of the infamous “Babington Plot.” For many years this was hailed as a triumph for Walsingham’s codebreaker, Thomas Phelippes. However, more recent evidence suggests that this might not have been a triumph of cryptanalysis at all. It may well be that the cipher key was simply handed over by Gilbert Gifford, a double (possibly triple) agent recruited in the field about a year earlier. Good old fashioned spy skills triumphing over mathematics yet again.

Indeed, the difference between spies and cryptanalysts may be amply illustrated by an anecdote that Kim Philby used to tell. During the Second World War he travelled to Bletchley Park and, as a trusted MI6 officer, he was shown some of the work that they were doing. A cryptanalyst showed Philby a partially decrypted message which said that Mussolini was travelling to the Brenner Pass to meet with a senior German politician whose name was H_TL_R.

“Could it by any chance be: ‘Hitler’?” suggested Philby.

The cryptanalyst looked at Kim over the top of his spectacles:

“Well, of course it bloody well is!” he exclaimed as if talking to a moron, “But there’s no way of proving it!”

One final point: the book has a number of appendices containing code challenges of increasing complexity. When the book was published there was a £10,000 prize for whoever managed to crack all of the codes first. That prize was won long ago. The puzzles remain as they are still interesting and – if you are some kind of mental masochist – fun. These days, would be codebreakers can also tackle the series of GCHQ puzzle books that are available. Yet another step in GCHQ’s recent publicity and recruitment drive.

The Code Book may be getting a bit long in the tooth now (it was first published in 1999). But the possibilities of quantum computing are still at the leading edge of the encryption story so the book has lost very little. It is still a valuable resource for anyone looking for a comprehensive introduction to the topic. Recommended.

[NB Our book reviews are not assessments of the literary value of the work. They are written by intelligence professionals and are concerned with the book’s accuracy, relevance to the realities of espionage, place in espionage history, etc.]

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