Exercise 9 |
1. (2) The Diffie-Hellman key exchange is being used to establish a secret key between Alice and Bob. Alice sends (719,3,191); Bob replies with 543. Alice's secret number, x, is 16. What is the key?
2. (3) In Figure 8-39, A is for the name Alice and B is Bob. Why is A sent in plaintext along with the encrypted message? Must all communication pass through the KDC? Explain.
3. (3) Alice wants to communicate with Bob using public-key cryptography. She contacts someone she hopes is Bob and asks for his key. Bob sends public key in plaintext and X.509 certificate signed by the root CA. Alice has the public key for the root CA. What steps does Alice take to verify that she is talking to Bob? Assume that Bob does not care who he is talking to.
Alice now knows that she received Bob's certificate but is it possible someone else sent it?
4. (2) Suppose an organization uses VPN to securely connect its sites over the Internet. Is there a need for a user, Jim, in this organization to use encryption or other security mechanism to communicate with another user in the organization? Explain.
5. (2) Give 2 reasons why PGP compresses messages.
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