viii CONTENTS
3.8. Problems 75
Chapter 4. Classical Cryptography: Attacks I 81
4.1. Breaking the Caesar Cipher 81
4.2. Function Preliminaries 84
4.3. Modular Arithmetic and the Affine Cipher 86
4.4. Breaking the Affine Cipher 91
4.5. The Substitution Alphabet Cipher 94
4.6. Frequency Analysis and the Vigen` ere Cipher 99
4.7. The Kasiski Test 102
4.8. Summary 106
4.9. Problems 107
Chapter 5. Classical Cryptography: Attacks II 113
5.1. Breaking the Permutation Cipher 114
5.2. Breaking the Hill Cipher 115
5.3. Running Key Ciphers 120
5.4. One-Time Pads 122
5.5. Summary 127
5.6. Problems 128
Chapter 6. Modern Symmetric Encryption 133
6.1. Binary Numbers and Message Streams 133
6.2. Linear Feedback Shift Registers 138
6.3. Known-Plaintext Attack on LFSR Stream Ciphers 142
6.4. LFSRsum 145
6.5. BabyCSS 150
6.6. Breaking BabyCSS 152
6.7. BabyBlock 158
6.8. Security of BabyBlock 161
6.9. Meet-in-the-Middle Attacks 162
6.10. Summary 164
6.11. Problems 164
Chapter 7. Introduction to Public-Channel Cryptography 171
7.1. The Perfect Code Cryptography System 173
7.2. KidRSA 180
7.3. The Euclidean Algorithm 182
7.4. Binary Expansion and Fast Modular Exponentiation 188
7.5. Prime Numbers 192
7.6. Fermat’s little Theorem 198
7.7. Summary 203
7.8. Problems 203
Chapter 8. Public-Channel Cryptography 213
8.1. RSA 214
8.2. RSA and Symmetric Encryption 218
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