Day1Fall06

# Day1Fall06 - An Introduction to Cryptology and Coding...

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An Introduction to Cryptology and Coding Theory Sarah Spence Adams Olin College sarah.adams@olin.edu Gordon Prichett Babson College prichett@babson.edu

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Communication System Digital Source Digital Sink Source Encoding Source Decoding Encryption Decryption Error Control Encoding Error Control Decoding Modulation Channel Demodulation
Cryptology Cryptography Inventing cipher systems; protecting communications and storage Cryptanalysis Breaking cipher systems

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Cryptography
Cryptanalysis

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What is used in Cryptology? Cryptography: Linear algebra, abstract algebra, number theory Cryptanalysis: Probability, statistics, combinatorics, computing
Caesar Cipher ABCDEFGHIJKLMNOPQRSTUVWXYZ Key = 3 DEFGHIJKLMNOPQRSTUVWXYZABC Example Plaintext: OLINCOLLEGE Encryption: Shift by KEY = 3 Ciphertext: ROLQFROOHJH Decryption: Shift backwards by KEY = 3

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Cryptanalysis of Caesar Try all 26 possible shifts Frequency analysis
Substitution Cipher Permute A-Z randomly: A B C D E F G H I J K L M N O P… becomes H Q A W I N F T E B X S F O P C… Substitute H for A, Q for B, etc. Example Plaintext: OLINCOLLEGE Key: PSEOAPSSIFI

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Cryptanalysis of Substitution Ciphers Try all 26! permutations – TOO MANY! Bigger than Avogadro's Number! Frequency analysis
Map A, B, C, … Z to 0, 1, 2, …25 A B … M N T U 0 1 … 13 14 20 21 Plaintext: MATHISUSEFULANDFUN Key: NGUJKAMOCTLNYBCIAZ

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## This note was uploaded on 11/11/2011 for the course MATH 110 taught by Professor Staff during the Winter '08 term at BYU.

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Day1Fall06 - An Introduction to Cryptology and Coding...

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