Another thinking one: Select the best answer (closest proximity.) The original DES cipher used a 56-bit key (Trivia note: 64-bit keys were required, but 8 bits were discarded in the actual algorithm. Hence, we only consider a DES key as a 56-bit key). Using a brute-force approach, how many keys must the cryptanalyst test in the worst-case scenario and how long will it take her to test all of them? Assume that she can test a billion (109) keys a second. (THINK!!!!) (T. A. 256 keys must be tested and it will take a little over 2000 years to test them all. B. 56 keys must be tested and it will take 56 nanoseconds to test them all. C. 56 ! (! is the notation for factorial) keys need to be tested and it will take 2.51070 years to test them all. D. 256 keys must be tested and it will take a little over 2.1 years to test them all. E. 56 ! (! is the notation for factorial) keys need to be tested and it will take 2.51081 years to test them all