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.

USERS	ALICERC	BORBC	CYNDYRC
ALICE	OX	R	NO ACCESS
BOB	R	OX	NO ACCESS
CYNDY	R	RW	ORWX

Cyndy gives Alice permission to read cyndyrc, and Alice removes Bob's ability to read alicerc.

USERS	ALICERC	BORBC	CYNDYRC
ALICE	OX	R	R
BOB	NO ACCESS	OX	NO ACCESS
CYNDY	R	RW	ORWX

Ease of	Per-subject access control	Per-object access control	Access control matrix	Capability
Determining authorized access during execution	Good/easy	Good/easy	Good/easy	Excellent
Adding access for a new subject	Good/easy	Excellent	Not easy	Excellent
Deleting access by a subject	Excellent	Excellent	Excellent	Excellent
Creating a new object to which all subjects by default have access	Not easy	Excellent	Easy	Easy

Question 1.

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.

Question 2.

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.