Using integer congruence and modular arithmetic to do shift ciphers on a spreadsheet. Day 2 of minicourse for MAT 140: Introduction to the Mathematical Sciences.

1. Cryptology
Day 2: Codemaking
as mathematics
MAT 140: Introduction to the
Mathematical Sciences
17 September 2008
Robert Talbert, PhD
Associate Professor of Mathematics
and Computing Science
rtalbert@franklincollege.edu
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2. Recap of Day 1
• Cryptology
• Shift cipher; plaintext; ciphertext; the encryption process
• Key; keyspace; brute force attack and exhaustive keyspace
search
• Monoalphabetic substitution; statistical attacks
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3. Shift cipher keys
0 = 26 = 52 = 78 = -26 = ...
1 = 27 = 53 = 79 = -25 = ...
2 = 28 = 54 = 80 = -24 = ...
...
24 = 50 = 76 = 102 = -2 = ...
25 = 51 = 77 = 103 = -1 = ...
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