Book Review: The Code Book
By Simon Singh. Published by Fourth Estate, ISBN 1-85702-879-1. UK Price ??.??
From Mary Queen of Scots to Quantum Computing
This book defies categorisation.
Is it a political/military history ? Yes. Since it is clear that the history of creating and trying to break cyphers is part-and-parcel of history, and particularly military history.
Is it a mathematics or computer book ? Again, yes, since you must expect to deal with some deep mathematical theory on the way. And where would the Internet be without PKI, the idea of a code that is both unbreakable, and publically known.
Or is this a bit of an intellectual "Boys Own" adventure ?
Right again, since you are following one of the age-old good-against-evil contests, where sometimes the bad guys win, and sometimes the good guys get on top. Of course, it is a matter of debate whether the good guys are the code breakers, or the code creators. It all depends upon whether you are interested in keeping a secret, or finding out the secrets of others.
The "Unbreakable" Code
Although the first chapter starts at the famous Mary Queen of Scots cypher, and the political intrigue of the Elizabethan court, this is just the backdrop to the crypographic art. By examining the Mary Cypher, Simon not only shows how clever it was (and by implication - how clever the code crackers were), but casts it into the historical context. Hence we get a review of the earliest Caeser Cypher, through the Dark Ages and on to the state of code making at that time.
The Caeser Cypher, by the way, is the simple "sliding alphabet", beloved of schoolboy codes. And for many years, this code was in genuine use. But, by making use of cryptanalysis, it is possible to crack this code fairly easily.
The "Unbreakable Code" ("Le Chiffre Indechiffrable"), on the other hand, was theoretically unable to succumb to cryptographic analysis. Until Babbage - a name well known to computer historians - was able to show how it could be cracked. So the battle between code creators and breakers had been joined.
Wartime Stories and Enigma
What Simon Singh is able to show is that even so-called uncrackable codes could be broken by clever use of intuitive techniques and mathematical theory.
The way in which this has been done appears little short of magic on first inspection, but Simon explains the logic with a clarity which contains the "of course" impact. Suddenly, the reader realises that even complex codes can be broken. And the approach is never to use the brute force ("try every combination until one works"). Instead, there are significant shortcuts to many of these approaches.
One example of this was the breaking of the German Enigma codes during World War Two. Here, a slight lack of randomness, a few lucky breaks, and dogged hard work, was able to help the Allies change the course of the war.
Could PKI be cracked ?
One of the disturbing parts of this book is the way in which clearly "uncrackable" cyphers have, in fact, been broken. And the way in which they have been addressed have been in the form of "obvious" pattern analysis. This raises an interesting question - would it be possible to break a Public Key Infrastructure key ?
PKI is part and parcel of the Internet. When you make a transaction, and the "padlock" symbol appears on your browser, you are using PKI. It works by having a public key, and your own private key. These are mathematically linked, but it is not possible to derive one from the other. OR IS IT ? IF (big, frightening, IF) someone somewhere could work out a way of deriving an individual's private key from knowing his public one, that person could become the hacker of all time, able to evesdrop on every email and secure transaction on the World Wide Web.
So could it be done ? Theoretically, as Simon has shown, this is impossible. But I have to say that for literally centuries people were convinced that "Le Chiffre Indechiffrable" was uncrackable. Until Babbage came along, everyone was convinced that the only was to crack that code was by brute force. Exactly the same opinion which is held about PKI today.
More worrying still, is it possible that someone in GCHQ, or the CIA has already worked out a shorthand way of identifying all the unique prime factors for a large number ? If so, they won't be telling anyone. Just like Clifford Cocks, who came up with an idea for an asymmetric cipher years before RSA "invented" it. Cocks' secret was burried by the UK Security Service, for Security Reasons.
The game of code-creating and cracking is still very much alive. And living in the World Wide Web.
A THOROUGHLY ENJOYABLE COMBINATION OF INTELLECTUAL CHALLENGE AND HISTORICAL READ.
Simon has also written a book on "Fermat's Last Theorem". I must find a copy.
Book Reviewed by Dennis Adams in November 2000.
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