HW #4_ SECURITY - IS2150 Homework#4 Introduction to...

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IS2150 Introduction to Security prp14 Homework #4 IS2150/TEL2810 Introduction to Security Homework 4 Total Points: 100 Due Date: Oct 20, 2009 Q.1) From Section 6.6 Do exercise 1, 3 (Points 20) SOLUTION: Exercise 6.6 #1: Let S L S C be the security clearance and category set of the security level L. According to Bell- LaPadula model, a subject in L and read an entity in L 1 if S L 1 < S L and S C 1 C S C . As the security and integrity levels are the same, S L S C also defines integrity clearance and category set of integrity level L. Now, the Biba’s model allows a subject in L to read an entity in L 1 , if and only if, L 1 dominated L. So this means that S L < S L 1 and S C C S C 1 . Now combining these together, L can read an entity in L 1 if, and only if, S L 1 < S L , S L < S L 1 AND S C C S C 1 , S C 1 C S C . This means that the subject and the entity being read must be in the same security level. Similarly, the subject and the entity being written must also be in the same security level. SOLUTION:Exercise 6.6 #3: The TPs can be executed in parallel provided the Bernstein conditions are met. However the problem may occur when the two of them try to update/write the same CDI at the same time. Now, the Bernstein conditions states that multiple processes can read an object at the same time but only one process can write to it and during that time, no process may read that object. This ensures that the values in the object are consistent with the updates.
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