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Mohamed G. Gouda                                        CS386M
Homework # 3                                            Spring 2005
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1. It is required to design a password authentication protocol between a
   client c and a server s. The protocol satisfies the following
   conditions:
   (1) Client c knows its password p, but server s does not know p.
   (2) Neither user c nor server s have any (shared, public, private or
       individual) key.
   (3) The protocol can overcome any attack of the following form:
       The attacker can replay any message, which is sent in the past
       between s and c during a successful senario that concluded by
       s authenticating c, and make s authenticate the attacker as c.

2. Solve problem 11 in Chapter 18.

3. Prove or disprove the following statement:
   No protocol in which each message is encrypted by one or more
   public keys can achieve authentication.

4. Solve problem 10 in Chapter 20.