Homework #3

CMPS 122, Spring 2004

Assigned:	26 April 2004
Due:	4 May 2004 at 11:59 PM

Please read the homework guidelines for information about how to work on the assignment and how to submit it.

1. For this problem, you're going to need to learn how to use PGP or GPG. You can install a free GPG client if necessary, or you can use a PGP client—they're interoperable (to some extent...).
   1. Create a public / private key pair for yourself using DSA and El-Gamal. Submit the public key to the MIT key server (http://pgp.mit.edu/). You may use an existing key of your own if you already have one.
   2. Email a (short) signed message to cmps122-staff [at] ucsc [dot] edu . Include the phrase "CMPS 122" in the subject. This message should not be encrypted, but must be signed by your private key.
2. In a public key system using RSA, you intercept the ciphertext C=46922 sent from Alice to Bob. Bob's public key is e=20235, n=62113. You'll need to explain how you got your answers, and include in your solution any simple program(s) that you might have written. HINT: the Unix program bc can do exact math on numbers of any length (including greater than 32 bits).
   1. What is the plaintext M?
   2. What is Bob's private key?
3. Problem 9.12 in Stallings (page 281).
4. Problem 11.6 in Stallings (page 340).
5. Problem 13.8 in Stallings (page 396).

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Last updated 26 Apr 2004 by Ethan L. Miller (elm at ucsc d0t edu)