Explain which implementation of the protection matrix is more suitable for the following

(a) granting read access to a file for all users.
(b) revoking write access to a file from all users.
(c) granting write access to a file to john, lisa, christie, and jeff.
(d) revoking execute access to a file from jana, mike, molly, and shane.

See explanation.

Explanation:

(a)

• To grant read access to a file for all users, access control list (ACL) is the best option.

o Create a group called 'all' with all users in it (assume the group name as 'all').

o Make a ACL for the file name with ACL as 'all:R'.

• It can also be done with capability list. With capability lists. it is sufficient to place the capability for the file in appropriate place in a capability system.

(b)

• To revoke write access for a file from all users, access control list (ACL) is the best option.

o Edit the ACL by removing the write access.

o If the group 'all: W' was the entry added to ACL, remove it from the ACL.

• It can also be done with capability list by changing the check field stored with the object.

(c)

• To grant write access to a file to John, Lisa. Christie and Jeff either the access control list method or the capability list can be used.

• It can be implemented with ACL as follows:

o Construct ACL for the file for all users,

o Then the ACL for file would be 'Christie, Jeff. John, Lisa: W'.

• It can be implemented using capability list method as follows:

o First construct the capability list for the file, 'file:W'.

o Then assign the above capability for each user named John, Lisa, Christie and Jeff.  

(d)

• To revoke execute access for a file from Jana, Mike, Molly, and Shane, access control lists are the only possibility.

o Edit the ACL by removing the execute access.

Hope this hels!