1. Explain multi-factor (multiple means of) authentication of a user and give two examples for each authentication factor.

2. Describe the fundamental principles in both the Bell-LaPadula and Biba security models. For each, explain what sort of security the model is intended to provide, the two key properties of the model, and then explain in your own words why each of the properties makes sense from a security standpoint.

3. Define the principle of defense in depth. Give two examples of how the principle might be applied: one describing security measures across multiple layers of security architecture, and another describing security measures within a single layer.

4. Alan and Beatrice are both users of PKI. Explain how they use their keys to communicate when Alan sends a private message to Beatrice, and provides proof that he sent the message.

5. Compare and contrast Mandatory Access Control and Discretionary Access Control. How well are they supported in various well-known (common) operating systems?