Homework Access Control 1. Consider a computer system with three users: Alice, Bob, and Cyndy. Alice owns the file alicerc, and Bob and Cyndy can read it. Cyndy can read and write Bob's file bobrc, but Alice can only read it. Only Cyndy can read and write her file cyndyrc. Assume that the owner of each of these files can execute it. a. Create the corresponding access control matrix. b. Cyndy gives Alice permission to read cyndyrc, and Alice removes Bob's ability to read alicerc. Show the new access control matrix. 2. Describe each of the following four kinds of access control mechanisms in terms of (a) ease of determining authorized access during execution, (b) ease of adding access for a new subject, (c) ease of deleting access by a subject, and (d) ease of creating a new object to which all subjects by default have access. a. per-subject access control list (that is, one list for each subject tells all the objects to which that subject has access) b. per-object access control list (that is, one list for each object tells all the subjects who have access to that object) c. access control matrix d. capability 3. Suppose a per-subject access control list is used. Deleting an object in such a system is inconvenient because all changes must be made to the control lists of all subjects who did have access to the object. Suggest an alternative, less costly means of handling deletion. 4. One feature of a capability-based protection system is the ability of one process to transfer a copy of a capability to another process. Describe a situation in which one process should be able to transfer a capability to another