Information Systems for Business and Beyond (2019)

Labs 1. The Caesar Cipher. One of the oldest methods of encryption was used by Julius Caesar and involved simply shifting text a specified number of positions in the alphabet. The number of shifted positions is known as the key. So, a key = 3 would encrypt ZOO to CRR. Decrypt the following message which has a key = 3: FRPSXWHU 2. The Vigenere Cipher . This cipher was used as recently as the Civil War by the Confederate forces. The key is slightly more complex than the Caesar Cipher. Vigenere used the number of letters after ‘A’ for his key. For example, if the key = COD, the first letter in the cypher is shifted 2 characters (because “C” is 2 letters after the letter ‘A’), the second letter is shifted 14 letters (O being 14 letters after ‘A’), and the third letter is shifted 3 letters (D being 3 letters after ‘A’). Then the pattern is repeated for subsequent letters. Decrypt the following message which has a key = COD: YSPGSWCHGCKQ 3. Frequency and Pattern Analysis . If you’ve ever watched Wheel of Fortune you know that contestants look for patterns and frequencies in trying to solve a puzzle. Your job in this lab is to analyze letter frequency and letter patterns to determine the plaintext message which in this case is a single word. The key is a simple substitution where the same letter in plaintext always results in the same letter in the cyphertext. The most frequently used letters in the English language are: E, A, O, I, T, S, N. Pattern analysis includes knowing words that have double letters such as “school.” Other patterns include “ing” at the end of a word, “qu” and “th” as a pair of letters. Cyphertext = CAGGJ. What is the key and the plaintext? Information Systems for Business and Beyond (2019) pg. 139

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