1. Distinguish between vulnerability, threat, and control.
2. Theft usually results in some kind of harm. For example, if someone steals your car, you may suffer financial loss, inconvenience (by losing your mode of transportation), and emotional upset (because of invasion of your personal property and space). List three kinds of harm a company might experience from theft of computer equipment.
3. List at least three kinds of harm a company could experience from electronic espionage or unauthorized viewing of confidential company materials.
4. List at least three kinds of damage a company could suffer when the integrity of a program or company data is compromised.
5. List at least three kinds of harm a company could encounter from loss of service, that is, failure of availability. List the product or capability to which access is lost, and explain how this loss hurts the company.
6. 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.
• per-subject access control list (that is, one list for each subject tells all the objects to which that subject has access)
• per-object access control list (that is, one list for each object tells all the subjects who have access to that object)
• access control matrix
• capability
7. 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.
8. File access control relates largely to the secrecy dimension of security. What is the relationship between an access control matrix and the integrity of the objects to which access is being controlled?
9. 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.
10. Suggest an efficient scheme for maintaining a per-user protection scheme. That is, the system maintains one directory per user, and that directory lists all the objects to which the user is allowed access. Your design should address the needs of a system with 1000 users, of whom no more than 20 are active at any time. Each user has an average of 200 permitted objects; there are 50,000 total objects in the system.
11. Give an example of the use of physical separation for security in a computing environment.
12. Give an example of the use of temporal separation for security in a computing environment.
13. Give an example of an object whose sensitivity may change during execution.
14. Respond to the allegation "An operating system requires no protection for its executable code (in memory) because that code is a duplicate of code maintained on disk."
15. Explain how a fence register is used for relocating a user's program.
16. Can any number of concurrent processes be protected from one another by just one pair of base/bounds registers?
17. The discussion of base/bounds registers implies that program code is execute only and that data areas are read-write-only. Is this ever not the case? Explain your answer.
18. A design using tag bits presupposes that adjacent memory locations hold dissimilar things: a line of code, a piece of data, a line of code, two pieces of data, and so forth. Most programs do not look like that. How can tag bits be appropriate in a situation in which programs have the more conventional arrangement of code and data?
19. What are some other modes of access that users might want to apply to code or data, in addition to the common read, write, and execute permission?
20. If two users share access to a segment, they must do so by the same name. Must their protection rights to it be the same? Why or why not?