Question: What happens when a UE sends a NAS message that needs to be both ciphered and integrity protected?
Option 1: The NAS message is first integrity protected and then ciphered.
Option 2: The NAS message is first ciphered and then the ciphered NAS message and the NAS sequence number are integrity protected by calculating the MAC.
Option 3: The NAS message is only ciphered, without any integrity protection.
Option 4: The NAS message is only integrity protected, without any ciphering.
Explanation: According to the text, when a NAS message needs to be sent both ciphered and integrity protected, the NAS message is first ciphered and then the ciphered NAS message and the NAS sequence number are integrity protected by calculating the MAC. This ensures that the message is both confidential (through ciphering) and authentic (through integrity protection).