Answer Happy

Exercise 5.5.1 Consider the following scenario. There are two grades of gaso- line: P for premium gasoline and R for regular gasoline. There are also two pumps (Pump1 and Pump2) and two cars: one car (RGC) uses regular gasoline and the other car (PGC) requires premium gasoline. Assume that the typical relation on gasoline grades holds: premium gasoline is higher quality than regular gasoline. You may also assume that cars specified as taking a particular grade of gasoline can safely take that grade of gasoline or higher. a. Provide the additional arrows (along with their proper labels) necessary for Figure 5.8 to satisfy the following: (a) Biba's strict integrity policy, and (b) Fuel requirements on cars.

b. Based on your completed diagram, for each pump below, give their domains: Pump1 = Pump2 c. Using P for Premium grade and R for regular grade, fill out the level assign- ments for the subject and objects in the following table: Subjects and Objects Integrity Level Premium Gas Tank PGT Regular Gas Tank RGT Pump1 Pump2 Premium Gas Car PGC Regular Gas Car RGC d. Fill in the access-control matrix: Subject PGT RGT PGC RGC

Regular Gas Tank RGT Pump) Pump2 Premium Gas Car PGC Regular Gas Car RGC d. Fill in the access-control matrix: Subject | PGT RGT PGC RGC Pump1 Pump2 e. Express as a formula in the access-control logic the policy that states that Pump/ can put into PGC. f. Propose a derived inference rule that states that Pump/ can put gasoline into PGC. Give a formal proof of the derived rule.