Question and answers – 20

3 to 4 line answers only each.

No Plagarism.


Need by 10/9/2016 – 10:00 AM


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



12. Give an example of the use of temporal separation for security in a computing



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?



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