$$An organisation is using the Bell$$LaPadula security model to control their

communications and controlling all their communications. They have a

bulletin board which all staff can post messages on to$.$ Given that Alice has

top clearance $($level $4),$ Bob has middle clearance $($level $2),$ Karen $($level $1)$ and Derek

has low level clearance $($level $0).$ Bob posts a message inviting all staff to

a BBQ$.$ Answer questions $7$ and $8,$ assuming all staff who receive a message, reply

to it on the bulletin board by the end of the working day.

Q$7$

What messages would Karen $($level $1)$ staff be able to read from the

board at the end of the day $($when everyone would have replied$).$

a$)$ No messages

b$)$ Messages from Alice and Bob only

c$)$ Messages from Alice, Bob and Derek only

d$)$ Messages from Alice, Bob, Derek and Karen only

e$)$ Messages from

Q$8$

What messages would Bob be able to read at the end of the day?

a$)$ No messages

b$)$ Only his own only

c$)$ Alice and his own messages only

d$)$ His own message$$s and Karen and Derek

e$)$ No messages

Q$9$

Assuming everyone wants to go to the BBQ$,$ who will be there?

a$)$ Everyone only

b$)$ No one only

c$)$ Alice and Bob only

d$)$ Alice, Bob and Derek only

e$)$ Bob only

Q$10$

What is authentication?

a$)$ Checking messages have not been altered

b$)$ Keeping messages secret

c$)$ Keeping messages with a timestamp

d$)$ Verifying the identity of a user of the system

e$)$ Controlling access rights to data