Over the years, I have been interviewed several times by various journalists. Below is a compilation of some of the questions that I have been asked about The Code Book and cryptography in general, and my answers to those questions.

Secrets, mysteries, puzzles: what makes them so appealing to almost everyone?

Cryptography is the science of secrecy. It is about the development of techniques that allow us to protect our secrets, and we all have secrets. Ever since people began to write, I imagine that people have invented methods of encrypting those texts that contained illicit affairs, military plans or recipes for alchemy. It is very natural for everybody to want to protect their secrets, and similarly we all want to find out the secrets of others, which is where code breaking becomes relevant.

So you can see that cryptography is a subject that should be of interest to many people, especially because we now live in the Information Age, and our secrets can be transmitted in so many ways – email, cell phone, etc. – and all these channels need to be protected.

How did you get the idea for The Code Book?

My first book, Fermat’s Last Theorem, was the history of a notorious mathematical problem, and it included a short section on how mathematicians use computers, and how computer development was driven by code breaking in the Second World War. This brief encounter with code breaking fired my imagination and I thought about writing a history of code breaking going back 2,000 years and coming up to the present Information Age.

I once heard how a biographer took a minor character from his last book and turned him or her into the main subject of his next biography. This is effectively what happened in my case – the minor character of cryptography in my first book became the major figure in my second book.

Did this accidental interest in cryptography pay off?

There were four main reasons why cryptography is an ideal topic for a book. First, the science is fascinating. The continual battle between codemakers and codebreakers is full of brilliant discoveries, which are elegant, ingenious and often completely counterintuitive. Second, this is a science with a history that goes back over 2,500 years. When explaining scientific ideas, it really helps to have a history. As a writer and populariser, it means that I can begin with earliest ideas, which are relatively easy to explain, and then gradually develop towards more sophisticated concepts. Third, secret codes are at the centre of some wonderful stories, including the execution of Mary Queen of Scots and the pivotal Zimmermann Telegram in the First World War. Once again, from a writer’s point of view, it was great to have such enthralling stories to rely on. They illustrate the significance of secret codes, they are gripping, and they provide a variation in pace against the more purely scientific passages. Fourth, and finally, secret codes are more relevant today than ever before. For the first two-thirds of the book the reader learns some great science and reads some great history, but in the final third there should be the realisation that codes are having a very real impact as we enter the 21st century and the Information Age. It is said that codes will provide the locks and keys of the Information Age. You can’t send personal e-mails without using cryptography to guarantee privacy and you can’t have e-commerce without using cryptography to secure your credit card details, and so on.

What is your favourite chapter or passage in The Code Book and why?

My favourite story concerns the secret discovery of the most important form of encryption of the twentieth century, one that has transformed security in the Information Age. The code breakers worked behind the closed doors of a British Government research centre, so their work was immediately classified and they received no credit for their work. Their idea was subsequently re-invented in America, but the British code breakers continued to receive no credit. After 25 years of secrecy, whilst I was writing the book, the British Government went public.

I am particularly fond of this story because I feel privileged to be the first to write about it at length. Also, the theme of the anonymous code breaker recurs throughout the book. Code breakers, by dint of what they do, rarely get the credit they deserve. The science of secrecy is a secret science.

Which parts of The Code Book did you enjoy researching the most?

For me the most fascinating aspect of writing The Code Book was learning about each new code, and thinking that it seemed unbreakable. Then after a bit more research I realised how each code could be broken. The real buzz was that moment when I discovered the weakness in each code, when I suddenly realised out to unravel a particular code.

Which chapter or passage of The Code Book was hardest to write and why?

The breaking of the German Enigma cipher used in the Second World War was an extraordinary difficult chapter to write. The story is remarkable, but unless a science writer can also explain the science then there is a certain emptiness. I struggled with the subject for several months, and I think that I have succeeded in providing a clear explanation. I worked closely with an illustrator who was able to draw some elucidating diagrams, which I think will help readers to understand how the Enigma works.

And I have now created a cryptography CD-ROM which animates the Enigma, and this really makes its internal workings crystal clear. There is even an Enigma emulator so that you can encrypt your own messages.

What was the challenge for you in writing about the history of code breaking?

The main challenge was to decide which stories and which scientific breakthroughs to select. I wanted to create a digestible and accessible book, yet this is a subject that spans 4,000 years and appears in every continent. So I had to decide which stories were most important, which ones linked best with each other, and which were most exciting and interesting. For example, the Second World War involved numerous ciphers, but I concentrated on the making and breaking of the Enigma cipher, because this changed the course of the war and it represented an enormous leap forward for code makers until it was cracked … at which point it represented an enormous breakthrough for code breakers.

Does the beauty of mathematics lie beneath codes and code breaking?

Much of cryptography can be seen mathematically, but this is a subject that also involves linguistics, computer science and physics. The latest encryption system is called quantum cryptography. Many people see this as a book that is driven by mathematics, but I think that their view is jaundiced by the subject matter of my first book, Fermat’s Last Theorem. I think The Code Book contains a significant amount of mathematics, but it would be wrong to ignore all the other elements.

Have you now become a master code breaker?

No.