Which feature of WPA2 helps ensure that each packet is unique?

The Temporal Key Integrity Protocol (TKIP) is specifically designed to enhance the security of wireless networks using WPA and WPA2 by ensuring that each packet transmitted is unique. TKIP accomplishes this by employing a per-packet key mixing function that combines the original encryption key with a unique initialization vector (IV) for each packet. This results in different encryption keys for each transmission, which significantly mitigates the risk of replay attacks and makes it exceedingly difficult for an attacker to decipher the packets even if they capture them.

The unique packet identifiers make it much harder for an attacker to decrypt a packet based on previously captured data because each packet is not only encrypted but also has a unique key applied to it. This feature of TKIP is critical in maintaining the confidentiality and integrity of data transmitted over wireless networks, particularly in environments where security threats are prevalent.

The other options, while relevant to network security, do not specifically address the uniqueness of each transmitted packet in the same manner as TKIP. AES encryption, for example, is a strong encryption standard, but without unique keys for each packet (which TKIP provides), it doesn't inherently ensure the uniqueness of packets.