Consider the following protocol for adding money to a debit card. (i) User inserts debit card into debit card machine. (ii) Debit card machine determines current value of card (in dollars), which is...

Consider the following protocol for adding money to a debit card.

(i) User inserts debit card into debit card machine.

(ii) Debit card machine determines current value of card (in dollars), which is stored in variable x.

(m) User inserts dollars into debit card machine and the value of the inserted dollars is stored in variable y.

(iv) User presses enter button on debit card machine.

(v) Debit card machine writes value of x + y dollars to debit card and ejects card.

Recall the discussion of race conditions in the text. This particular protocol has a race condition.

a. What is the race condition in this protocol?

b. Describe a possible attack that exploits the race condition.

c. How could you change the protocol to eliminate the race condition, or at least make it more difficult to exploit?