# Hmk2-Sol - CIS 3362 Homework#2 Classical Polyalphabetic...

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CIS 3362 Homework #2 Classical Polyalphabetic, Polygraphic Ciphers Solutions 1) Using the index of coincidence test with 9 bins yields the following values for each bin: 6.26, 5.98, 6.46, 4.0, 4.3, 7.69, 7.38, 4.61, 5.53 None of the other bin sizes leads to any values above 6% (except for 3 bins). We can exclude 3 because the other two bins are much too small. Using both the mutual index of coincidence tool (matching with the English language) and the visual aid given in Cryptool, as well as matching a word to the first four letters, the beginning of the keyword becomes “CHAD”. From here, either subsequent guessing, or realizing that the Dolphins starting quarterback is Chad Henne, will help you complete the keyword to be “chadhenne”. Here is the corresponding plaintext: I will make this message slightly harder to break by omitting a particular word that you think will appear. But a digram from that word appears in this message often. Can you guess what word I am referring to? I really need to post this homework assignment soon so I will hurry up and finish this message. 2) A bin size of 8 reveals the following index of coincidences for each bin: 5.72, 7.13, 12.52, 8.14, 7.54, 6.28, 7.68, 6.42 This is clearly the length of the keyword. Using the mutual index of coincidence or the Cryptool graphs yields that “IN” are likely to be the first two letters of the keyword. The last two letters are likely to be “OR”, from there, using the given plaintext derived from plugging in these letters will reveal the keyword “inductor”. Here is the corresponding plaintext: Since I hid a prize last time I will hide another one this time to give everyone another chance. The prize will be the exact same thing as last time. To find out what it was you have to ask the person who won last time. Or maybe you can just figure it out by finding it this time. I will give the prize to a certain assistant in the office

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Hmk2-Sol - CIS 3362 Homework#2 Classical Polyalphabetic...

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