Question: What input parameters are used by the NAS ciphering algorithm for encrypting messages in a 5G System (5GS)?
Option 1: BEARER ID, DIRECTION bit, and NAS encryption key
Option 2: BEARER ID, DIRECTION bit, NAS COUNT, NAS encryption key, and the length of the key stream to be generated by the encryption algorithm
Option 3: NAS sequence number, NAS overflow counter, and NAS encryption key
Option 4: Length of the key stream, NAS message container IE, and CIoT small data container IE
Explanation: The correct answer is Option 2 because the NAS ciphering algorithm uses a combination of parameters including BEARER ID, DIRECTION bit, NAS COUNT (which includes the NAS sequence number and an estimate for the NAS overflow counter), NAS encryption key, and the length of the key stream to be generated by the encryption algorithm. This ensures secure encryption of messages in a 5G System (5GS).