Assume that passwords are selected from four-character combinations of 26 alphabetic characters. Assume that an adversary is able to attempt passwords at a rate of one per second.
a. Assuming no feedback to the adversary until each attempt has been completed, what is the expected time to discover the correct password?
b. Assuming feedback to the adversary flagging an error as each incorrect character is entered, what is the expected time to discover the correct password?