Homework 3_it223_Spring2017

# Homework 3_it223_Spring2017 - Homework 3 Cryptanalysis IT...

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Homework 3 Cryptanalysis IT 223 – 35 points total Please submit a DOC file. Do the best you can. Cheating (not Safe Assign, but other methods) will be considered an HCV. Do not help others with this assignment. Fractionation Systems In fractionation systems, letters are both substituted and transposed yielding the superencryption. First, the plain letters are substituted by selected letters (commonly pairs of letters are used, in which case the cipher is called a "biliteral cipher"). Secondly, such letters are then superencrypted by the transposition. Example: Let’s superencrypt "Probability" by using keywords "cyber" for the ADFGVX substitution and "crime" for the transposition matrix. Step 1 - ADFGVX substitution: One of the most famous field ciphers ever was a fractionation system - the ADFGVX Cipher which was employed by the German Army during the First World War. This system was so named because it used a 6 by 6 matrix to substitution-encrypt the 26 letters of the alphabet and 10 digits into pairs of the symbols A, D, F, G, V and X. The variable setup of the matrix is guaranteed through the choice of the keyword (here “cyber”) that precedes the remaining letters and digits. The resulting biliteral cipher is only the intermediate cipher; it is then written into the rectangular matrix and transposed to produce the final cipher that is the one that was transmitted.

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