Part 1: Concepts (20 marks; 4 marks each) Please answer the following questions in complete sentences. Your answer for each question should be about 150 words.

1. Why is it important to distinguish between mechanisms of protection and policies of protection?

2. What is an access matrix, and how can it be implemented?

3. How does a virus differ from a worm?

4. What is the difference between symmetric encryption and asymmetric encryption?

5. What are the two main varieties of authentication algorithms?