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# hw3 - With the help of a neat diagram describe signing...

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10/15/2009 CSE 565: Computer Security Due: 10/29/09 Homework 3 Problem 1: Problem No. 10.2 from Stallings. Problem 2: Diffie-Hellman key-exchange algorithm is subject to man-in-the-middle attack. Describe the steps of this attack (you can use the version discussed in the class, or use the version from the book, but remember to correct the errors in some of the steps given in the book). You then provide a version that is resilient to the main-in-the-middle attack (Hint: use digital signatures). You can get the solution from Trappe and Washington (Introduction to Cryptography with Coding Theory). If you do so, indicate the reference. Problem 3: (Optional) Problem No. 10.6 from Stallings. This problem was covered in the class in the context of El Gamal signature scheme. Problem 4: Problem No. 10.7 from Stallings. Note that this problem is related to the previous problem. Problem 5:
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Unformatted text preview: With the help of a neat diagram describe signing using the public-key encryption where ar-biter doesn’t see message. Explain how this protocol overcomes the alliances to defraud in the conventional encryption schemes. The solution can be found in the book. If you use the book, do not forget to make a reference to the book in your answer. Problem 6: Problem 13.9 from Stallings. Problem 7: (Optional) Suppose we use the ElGamal signature scheme with p=65539, α =2 and β =33384. Pablo wants to sign a message hi (809), and another, bye (22505). Note that the letters are coded as 01=a, 02=b, etc. The two signed messages (m,r,s) are: (809, 18357, 1042) and (22505, 18357, 26272). (a) Show that the same value of k was used for each signature. (b) Use this fact to Fnd this value of k and to Fnd the value of a such that β α a (mod p). 1...
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