Security in Computing, Third Edition

5.11. Exercises

1:	A principle of the Bell–La Padula model was not mentioned in this chapter. Called the tranquillity principle, it states that the classification of a subject or object does not change while it is being referenced. Explain the purpose of the tranquillity principle. What are the implications of a model in which the tranquillity principle is not true?
2:	Subjects can access objects, but they can also access other subjects. Describe how a reference monitor would control access in the case of a subject acting on another subject. Describe how a reference monitor would control access in the case of two subjects interacting.
3:	List the source and end of all information flows in each of the following statements. (a) sum := a+b+c; (b) if ...