The Code Book: The Secret History of Codes and Code-breaking

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Simon Singh. The Code Book: The Secret History of Codes and Code-breaking

The Code Book. The Secret History of Codes and Codebreaking. Simon Singh

Copyright

Dedication

Epigraph

Contents

Introduction

1 The Cipher of Mary Queen of Scots

2 Le Chiffre Indéchiffrable

3 The Mechanisation of Secrecy

4 Cracking the Enigma

5 The Language Barrier

6 Alice and Bob Go Public

7 Pretty Good Privacy

8 A Quantum Leap into the Future

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The Cipher Challenge

Appendix A

Appendix B

Appendix C

Appendix D

Appendix E

Appendix F

Appendix G

Appendix H

Appendix I

Appendix J

Glossary

Further Reading

Picture Credits

Searchable Terms

Acknowledgements

About the Author

Other Books by Simon Singh

About the Publisher

Отрывок из книги

For my mother and father,

Sawaran Kaur and Mehnga Singh

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At this point, we have confidently identified two of the letters in the ciphertext. Our conclusion that X = a is supported by the fact that X appears on its own in the ciphertext, and a is one of only two English words that consist of a single letter. The only other letter that appears on its own in the ciphertext is Y, and it seems highly likely that this represents the only other one-letter English word, which is i. Focusing on words with only one letter is a standard cryptanalytic trick, and I have included it among a list of cryptanalytic tips in Appendix B. This particular trick works only because this ciphertext still has spaces between the words. Often, a cryptographer will remove all the spaces to make it harder for an enemy interceptor to unscramble the message.

Although we have spaces between words, the following trick would also work where the ciphertext has been merged into a single string of characters. The trick allows us to spot the letter h, once we have already identified the letter e. In the English language, the letter h frequently goes before the letter e (as in the, then, they, etc.), but rarely after e. The table below shows how frequently the O, which we think represents e, goes before and after all the other letters in the ciphertext. The table suggests that B represents h, because it appears before O on 9 occasions, but it never goes after it. No other letter in the table has such an asymmetric relationship with O.

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