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					CSE 505A. Data Security: Homework 4

Due: November 29, Tuesday, 5:30pm
  1. Install and use the PGP email system. After reading Section 15.1, do
     the following: (50pt)

        a. Find, download, and install a PGP software available online.
           For example, a package for MS Windows is at:
           Report the software you used and the steps you followed.

        b. Generate a key pair for yourself. You may choose your preferred
           encryption algorithm and key size. DH/DSS algorithm and
           2048/1024 key size are recommended. Report your algorithm, key
           size, and your public key.

        c. Partner with another student in the class. Email him/her your
           public key in plain text and have him/her send you a PGP-
           encrypted email. Decrypt the message using your private key.
           Report all the steps you have taken in this practice. Compare the
           size of the message before and after decryption.

        d. Use PGP to encrypt and sign a large file (>10MB) in your
           computer. Then decrypt and verify the resulting file. Report the
           steps you used and the CPU time taken by each step. Also,
           compare the sizes of the original file, the encrypted and signed
           file, and the encrypted-then-decrypted file.

        e. It is known that public-key algorithms are slow and cannot
           efficiently handle large files. How do you explain the performance
           of PGP on large files?
2. Study the Kerberos V5 manual available online and answer the
   following questions, assuming that you are a user in a network domain
   using the Kerberos V5 login program. (30pt)

      a. What is the command for obtaining a ticket? What is the default
      lifetime for a ticket?

      b. Can you set a different lifetime for a ticket? How?

      c. Which command can show you all your tickets? From the
      resulting list of tickets, how can you tell which ones are the
      ticket-granting tickets?

      d. Assuming you are on a local host named h1.ker.wustl.edu and
      you want to use telnet to connect to the host named
      h2.ker.wustl.edu, and assuming you have no ticket yet, list the
      sequence of commands your need to use. For each command, list
      the tickets you have after executing it.

3. Problem 14.4. (20pt)
         Hint: Taking the normal integer eth root of an integer n is
         relatively easy.

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