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Cryptology - Unofficial St. Mary's College of California Web Site

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Contents<br />

List <strong>of</strong> Figures 8<br />

1 Caesar Ciphers 9<br />

1.1 Saint Cyr Slide . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12<br />

1.2 Running Down the Alphabet . . . . . . . . . . . . . . . . . . . . 14<br />

1.3 Frequency Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 15<br />

1.4 Linquist’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . 20<br />

1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22<br />

1.6 Topics and Techniques . . . . . . . . . . . . . . . . . . . . . . . . 22<br />

1.7 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23<br />

2 Cryptologic Terms 29<br />

3 The Introduction <strong>of</strong> Numbers 31<br />

3.1 The Remainder Operator . . . . . . . . . . . . . . . . . . . . . . 33<br />

3.2 Modular Arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . 38<br />

3.3 Decimation Ciphers . . . . . . . . . . . . . . . . . . . . . . . . . 40<br />

3.4 Deciphering Decimation Ciphers . . . . . . . . . . . . . . . . . . 42<br />

3.5 Multiplication vs. Addition . . . . . . . . . . . . . . . . . . . . . 44<br />

3.6 Koblitz’s Kid-RSA and Public Key Codes . . . . . . . . . . . . . 44<br />

3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48<br />

3.8 Topics and Techniques . . . . . . . . . . . . . . . . . . . . . . . . 48<br />

3.9 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49<br />

4 The Euclidean Algorithm 55<br />

4.1 Linear Ciphers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55<br />

4.2 GCD’s and the Euclidean Algorithm . . . . . . . . . . . . . . . . 56<br />

4.3 Multiplicative Inverses . . . . . . . . . . . . . . . . . . . . . . . . 59<br />

4.4 Deciphering Decimation and Linear Ciphers . . . . . . . . . . . . 63<br />

4.5 Breaking Decimation and Linear Ciphers . . . . . . . . . . . . . . 65<br />

4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67<br />

4.7 Topics and Techniques . . . . . . . . . . . . . . . . . . . . . . . . 67<br />

4.8 Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68<br />

3

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