Question

Consider a computer system with three users, Alice, Bob and Cindy. Alice owns the file alicerc, and Bob and Cindy can read it. Cindy can read the write the file bobrc, which Bob owns, but Alice can only read it. Only Cindy can read and write the file cyndyrc, which she owns. Assume that the owner of each of these files can execute it. Create the corresponding access control matrix Cindy gives Alice permission to read cyndyrc, and Alice removes Bob's ability to rad alicerc. Show the new access control matrix.

Answer 1

The first access control matrix:

Alice Bob Cindy

alicerc rwx r r

bobrc r rwx rw

cyndyrc rwx

The access control matrix after the new permissions:

• Bob will not have access to read alicerc. So, r is deleted in the CMA.
• Alice will have access to read cyndyrc. So, r is added to the CMA.

Alice Bob Cindy

alicerc rwx r

bobrc r rwx rw

cyndyrc r rwx