NAS Security Mode Command

Activating NAS Security

After authentication completes, the AMF activates NAS security by sending the Security Mode Command to the UE. This message carries the selected NAS encryption algorithm (NEA) and integrity algorithm (NIA), along with the replayed UE security capabilities. The supported algorithms include NEA0 (null), NEA1 (SNOW 3G), NEA2 (AES), and NEA3 (ZUC) for encryption, with corresponding NIA1, NIA2, and NIA3 for integrity. NIA0 (null integrity) is only permitted for emergency registration scenarios.