# HW7 - case? C. In what way does a cryptographic hash, e.g.,...

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CS 453: Networks Fall 2009 Homework 7 (Extra credit) Instructor: V. Arun Assigned: 12/07/09, Due: 12/14/09 Note: Please show as much of your work as you can. Whenever possible, use variable names before plugging in numerical values . Even if you get the answer wrong, you can get partial credit if you show your approach clearly. It will help us tell you where you made a mistake. If you plug in numbers right upfront and your answer is wrong, you will not get partial credit. Problem 1 (Quickies): A. Define confidentiality and message integrity. Can you have one without the other? Justify your answer. B. Suppose N people want communicate with each of N-1 other people using symmetric key encryption. All communication between any two people, i and j, is visible to all other people in this group of N, and no other person in this group should be able to decode their communication. How many keys are required in the system as a whole? Now suppose that public key encryption is used. How many keys are required in this
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Unformatted text preview: case? C. In what way does a cryptographic hash, e.g., MD5, provide better message integrity check than an Internet checksum? D. Consider a variation of the MAC algorithm (Figure 8.9 in text) where the sender sends (m, H(m)+s), where H(m) + s is the concatenation of H(m) and s. Is this variation flawed? Why or why not? Problem 2 (Mobile IP): Consider the diagram on slide 6-51, and suppose now that the correspondent (shown as being stationary in its home network in slide 6-51) and the mobile host shown in Figure 6-51 are both mobile. Draw the corresponding diagram for this case, showing the steps taken when the correspondent sends a datagram to the remote host and the remote host replies back to the correspondent. Problem 3 (Wireless): Problem P8 from Chapter 6. Problem 4 (Security): Problem P10 from Chapter 8. Problem 5 (Security): Problem 24 from Chapter 8....
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