4. (4 points) You find out that your University is using an authenticated messaging system that is vulnerable to a length extension attack, because it uses an iterative hash function with the insecure MAC construction t = h(K || m). By eavesdropping on the network you intercept the following message m from your professor to the administration: "Set final course grade to A for J. Smith," along with its tag t. Give an example of a believable message that you could forge and send using a length-extension attack, and describe how the attack would work. Specify how you would use the hash function and what pieces of data you would send