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hw4 - CMPSCI 177 Computer Security Fall 2011 Fourth...

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CMPSCI 177 - Computer Security Fall 2011 Fourth Homework - DES and Public Key Due: Tuesday, 25 OCT 11 2:00pm Part I: DES 1. Consider the following 64 bit key: 1000110110001011101101001010100111101011001010011011001011001100 What is the value of the key used for the fourth round of the DES encryption algorithm? 2. Consider the following 48 bit string: 101101010110011010110000010101011001101111011011 If this string is input to the s boxes in the DES encryption algorithm, what string is output from the s boxes? Part II: Public Key 1. What is the totient of 36? Defend your answer. 2. Use the superincreasing sequence S=[2,4,9,17,34,69,146], modulus n=311, and multiplier w=19 to gen- erate a public key sequence H for Merkle-Hellman. 3. Assume that you received the ciphertext C=101 from someone using the public key generated in exer- cise 2. You are to decipher C and determine the message M that was used to generate C. 4. Alice has chosen primes p=2357 and q=2551 and exponent e=3674911 to use with the RSA algorithm. What does Alice publish as her public key? 5. Suppose Alice receives the following message from Bob, who used the public key from exercise 4 to encrypt it: 3650502. Determine the plaintext that Alice obtains from this ciphertext.

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