Which of the following is one of the key lengths offered by AES?

• A. 112 bits
• B. 192 bits
• C. Both A and B
• D. Neither A nor B

Answer: (B)

AES uses a fixed 128-bit block size but supports three key lengths: 128, 192, and 256 bits. Because of that, 192 bits is a valid AES key length, while 112 bits is not defined for AES. The different key sizes also determine the number of rounds: 128-bit keys use 10 rounds, 192-bit keys use 12 rounds, and 256-bit keys use 14 rounds. So the correct choice is the 192-bit key length.