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Unformatted text preview: CIS 3362 Homework #1 Monoalphabetic Ciphers Solutions 1) Try each of the possible keys. To decrypt, shift by 10. Thus, the original encryption key was 16. Here is the message, with spaces and punctuation added: Welcome to crypto class! Hope this message wasnt so hard to break. 2) Brute force can also be applied to this cipher. Trying all 312 keys yields the original encryption keys to be a = 19, b = 6. (The corresponding decryption keys are a = 11, b = 12.) Here is the message below: While this one is harder, there is no reason you cant just try all of the possible keys. Dont forget to write down what the encryption function was. 3) By running a frequency analysis, we find the most frequent ciphertext letters: B 10.1% K 9.3% Q 10.7% U 11.8% It is more than likely that one of these four letters maps to the letter plaintext letter e. The trigram QLU appears 8 times in the cipher text and it is likely that this maps to the word, the. Other repeated blocks of text that starts with QL are QLPQ and QLKS. Other words the....
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This note was uploaded on 07/13/2011 for the course CIS 3362 taught by Professor Staff during the Fall '08 term at University of Central Florida.
 Fall '08
 Staff
 Information Security

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