Having discussed the evolution of codes and their impact on history, the book’s second objective is to demonstrate how the subject is more relevant today than ever before. As information becomes an increasingly valuable commodity, and as the communications revolution changes society, so the process of encoding messages, known as encryption, will play an increasing role in everyday life. Nowadays our phone calls bounce off satellites and our e-mails pass through various computers, and both forms of communication can be intercepted with ease, so jeopardising our privacy. Similarly, as more and more business is conducted over the Internet, safeguards must be put in place to protect companies and their clients. Encryption is the only way to protect our privacy and guarantee the success of the digital marketplace. The art of secret communication, otherwise known as cryptography, will provide the locks and keys of the Information Age.

However, the public’s growing demand for cryptography conflicts with the needs of law enforcement and national security. For decades, the police and the intelligence services have used wire-taps to gather evidence against terrorists and organised crime syndicates, but the recent development of ultra-strong codes threatens to undermine the value of wire-taps. As we enter the twenty-first century, civil libertarians are pressing for the widespread use of cryptography in order to protect the privacy of the individual. Arguing alongside them are businesses, who require strong cryptography in order to guarantee the security of transactions within the fast-growing world of Internet commerce. At the same time, the forces of law and order are lobbying governments to restrict the use of cryptography. The question is, which do we value more – our privacy or an effective police force? Or is there a compromise?

Although cryptography is now having a major impact on civilian activities, it should be noted that military cryptography remains an important subject. It has been said that the First World War was the chemists’ war, because mustard gas and chlorine were employed for the first time, and that the Second World War was the physicists’ war, because the atom bomb was detonated. Similarly, it has been argued that the Third World War would be the mathematicians’ war, because mathematicians will have control over the next great weapon of war – information. Mathematicians have been responsible for developing the codes that are currently used to protect military information. Not surprisingly, mathematicians are also at the forefront of the battle to break these codes.

While describing the evolution of codes and their impact on history, I have allowed myself a minor detour. Chapter 5 describes the decipherment of various ancient scripts, including Linear B and Egyptian hieroglyphics. Technically, cryptography concerns communications that are deliberately designed to keep secrets from an enemy, whereas the writings of ancient civilisations were not intended to be indecipherable: it is merely that we have lost the ability to interpret them. However, the skills required to uncover the meaning of archaeological texts are closely related to the art of codebreaking. Ever since reading The Decipherment of Linear B, John Chadwick’s description of how an ancient Mediterranean text was unravelled, I have been struck by the astounding intellectual achievements of those men and women who have been able to decipher the scripts of our ancestors, thereby allowing us to read about their civilisations, religions and everyday lives.

Turning to the purists, I should apologise for the title of this book. The Code Book is about more than just codes. The word ‘code’ refers to a very particular type of secret communication, one that has declined in use over the centuries. In a code, a word or phrase is replaced with a word, number or symbol. For example, secret agents have codenames, words that are used instead of their real names in order to mask their identities. Similarly, the phrase Attack at dawn could be replaced by the codeword Jupiter, and this word could be sent to a commander in the battlefield as a way of baffling the enemy. If headquarters and the commander have previously agreed on the code, then the meaning of Jupiter will be clear to the intended recipient, but it will mean nothing to an enemy who intercepts it. The alternative to a code is a cipher, a technique that acts at a more fundamental level, by replacing letters rather than whole words. For example, each letter in a phrase could be replaced by the next letter in the alphabet, so that A is replaced by B, B by C, and so on. Attack at dawn thus becomes Buubdl bu ebxo. Ciphers play an integral role in cryptography, and so this book should really have been called The Code and Cipher Book. I have, however, forsaken accuracy for snappiness.

As the need arises, I have defined the various technical terms used within cryptography. Although I have generally adhered to these definitions, there will be occasions when I use a term that is perhaps not technically accurate, but which I feel is more familiar to the nonspecialist. For example, when describing a person attempting to break a cipher, I have often used codebreaker rather than the more accurate cipherbreaker. I have done this only when the meaning of the word is obvious from the context. There is a glossary of terms at the end of the book. More often than not, though, crypto-jargon is quite transparent: for example, plaintext is the message before encryption, and ciphertext is the message after encryption.

Before concluding this introduction, I must mention a problem that faces any author who tackles the subject of cryptography: the science of secrecy is largely a secret science. Many of the heroes in this book never gained recognition for their work during their lifetimes because their contribution could not be publicly acknowledged while their invention was still of diplomatic or military value. While researching this book, I was able to talk to experts at Britain’s Government Communications Headquarters (GCHQ), who revealed details of extraordinary research done in the 1970s which has only just been declassified. As a result of this declassification, three of the world’s greatest cryptographers can now receive the credit they deserve. However, this recent revelation has merely served to remind me that there is a great deal more going on, of which neither I nor any other science writer is aware. Organisations such as GCHQ and America’s National Security Agency continue to conduct classified research into cryptography, which means that their breakthroughs remain secret and the individuals who make them remain anonymous.

Despite the problems of government secrecy and classified research, I have spent the final chapter of this book speculating about the future of codes and ciphers. Ultimately, this chapter is an attempt to see if we can predict who will win the evolutionary struggle between codemaker and codebreaker. Will codemakers ever design a truly unbreakable code and succeed in their quest for absolute secrecy? Or will codebreakers build a machine that can decipher any message? Bearing in mind that some of the greatest minds work in classified laboratories, and that they receive the bulk of research funds, it is clear that some of the statements in my final chapter may be inaccurate. For example, I state that quantum computers – machines potentially capable of breaking all today’s ciphers – are at a very primitive stage, but it is possible that somebody has already built one. The only people who are in a position to point out my errors are also those who are not at liberty to reveal them.

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