Question: When is a full 32-bit NAS-MAC appended to integrity-protected NAS messages, except for one specific case?
Option 1: Always, for all integrity-protected messages without exceptions.
Option 2: Never, only the 16 least significant bits are used for all messages.
Option 3: For all integrity-protected messages except the NAS Service Request message.
Option 4: Only for NAS Attach Request messages when the EPS security context is not deleted.
Explanation: A full 32-bit NAS-MAC is appended to all integrity-protected messages with one exception: for the NAS Service Request message, only the 16 least significant bits of the 32-bit NAS-MAC are appended, highlighting its unique handling in terms of integrity protection and MAC length.