Question: What is a key requirement for constructing an Initialization Vector (IV) for CBC mode in IP network layer security, as per Network Domain Security (NDS) specifications?
Option 1: The IV field must be exactly 16 octets, regardless of the cipher algorithm's block size, and chosen sequentially.
Option 2: The IV field shall be the same size as the block size of the cipher algorithm being used, and shall be chosen at random, ensuring unpredictability.
Option 3: The IV can be constructed from the encrypted data of the preceding encryption process to ensure efficiency.
Option 4: The IV must always be a fixed value, predetermined by the network architecture for simplicity.
Explanation: This option correctly reflects the strengthened requirement for CBC mode, emphasizing that the IV's size must match the cipher algorithm's block size and that it must be randomly chosen to ensure unpredictability. This is crucial for enhancing security against attacks that exploit predictable IVs, regardless of the underlying cipher algorithm's strength.