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# Homework 1 - 2 In this problem you will use a modified ECB...

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CIS 4363 Homework 1 Due: 2/15/2007 1. In this problem you will use a modified RC4 cipher. The text is encrypted at half a byte, 4 bits, at a time. Let’s call half a byte, 4 bits, as a unit. Vector S will be 16-unit long, from S[0] to S[15]. Each S[i] will have 4 bits, containing a number from 0 to 15. K will have a length equal or less then 16 units. Find the cipher text using the given K and plaintext. Hint: Convert each character to the ASCII code, which is a byte long. So every character will be converted into two units. You don’t need to convert cipher text back to characters, as you might end up with very strange characters. Just write every unit in hex, from 0 to F. An ASCII table is attached for your reference. a) K = “GOKNIGHT”, Plaintext = “FIRSTEXAM” b) K = “GETA”, Plaintext = “INCIS4363”

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Unformatted text preview: 2. In this problem you will use a modified ECB cipher. Instead of encrypting 64 bits at a time, encrypt a fixed length of characters at a time using Hill cipher. Find the cipher text using the given Hill cipher key and plaintext. Hint: Convert each character to a number between 0 and 25, as in Hill cipher. The fixed length is determined by Hill cipher key. a) = 3 19 8 7 K , Plaintext = “FIRSTEXAMX” b) = 19 21 5 2 18 17 2 21 17 K , Plaintext = “INTHISCOURSE” 3. Do problem 2 again with a modified Cipher Block Chaining Mode. Instead of XOR the plaintext block with the previous cipher text block, add them up character by character and then mod by 26. Hint: (11, 12) + (21, 22) = (11+21, 12+22) = (32, 34) = (6, 8)...
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