1. Explain the intuition behind the two rules in the Bell-LaPadula model for mandatory access control.

2. Give an example of how covert channels can be used to defeat the Bell-LaPadula model.

3. Give an example of polyinstantiation.

4. Describe a scenario in which mandatory access controls prevent a breach of security that cannot be prevented through discretionary controls.

5. Describe a scenario in which discretionary access controls are required to enforce a security policy that cannot be enforced using only mandatory controls.

6. If a DBMS already supports discretionary and mandatory access controls, is there a need for encryption?

7. Explain the need for each of the following limits in a statistical database system:

(a) A maximum on the number of queries a user can pose.

(b) A minimum on the number of tuples involved in answering a query.

(c) A maximum on the intersection of two queries (i.e., on the number of tuples that both queries examine).

8. Explain the use of an audit trail, with special reference to a statistical database system.

9. What is the role of the DBA with respect to security?

10. What is public-key encryption? How does it differ from the encryption approach taken in the Data Encryption Standard (DES), and in what ways is it better than DES?

11. What are one-way functions, and what role do they play in public-key encryption?

12. Explain how a company offering services on the Internet could use public-key encryption to make its order-entry process secure. Describe how you would use DES encryption for the same purpose, and contrast the public-key and DES approaches