Contents
Preface xi
Acknowledgments xvii
Chapter 1. Historical Introduction 1
1.1. Ancient Times 2
1.2. Cryptography During the Two World Wars 8
1.3. Postwar Cryptography, Computers, and Security 12
1.4. Summary 14
1.5. Problems 15
Chapter 2. Classical Cryptology: Methods 19
2.1. Ancient Cryptography 20
2.2. Substitution Alphabet Ciphers 22
2.3. The Caesar Cipher 24
2.4. Modular Arithmetic 26
2.5. Number Theory Notation 28
2.6. The Affine Cipher 30
2.7. The Vigen` ere Cipher 33
2.8. The Permutation Cipher 36
2.9. The Hill Cipher 39
2.10. Summary 42
2.11. Problems 42
Chapter 3. Enigma and Ultra 51
3.1. Setting the Stage 51
3.2. Some Counting 54
3.3. Enigma’s Security 60
3.4. Cracking the Enigma 67
3.5. Codes in World War II 70
3.6. Summary 72
3.7. Appendix: Proofs by Induction 73
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