3.5. Exercises
| 1: | The proof of Theorem 31 states the following: Suppose two subjects s1 and s2 are created and the rights in A[s1, o1] and A[s2, o2] are tested. The same test for A[s1, o1] and A[s1, o2] = A[s1, o2] A[s2, o2] will produce the same result. Justify this statement. Would it be true if one could test for the absence of rights as well as for the presence of rights? | | 2: | Devise an algorithm that determines whether or not a system is safe by enumerating all possible states. Is this problem NP-complete? Justify your answer. | | 3: | Prove Theorem 33. (Hint: Use a diagonalization argument to test each system as the set of protection systems is enumerated. Whenever a protection system leaks a right, add it to the list of unsafe protection systems.) |
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