A.14 K_AMF to K_ASME‘ derivation for interworking

33.5013GPPRelease 18Security architecture and procedures for 5G SystemTS

A.14.1 Idle mode mobility

This input string is used when there is a need to derive K’_ASME from K_AMF during mapping of security contexts from 5G to EPS at idle mode mobility. The following input parameters shall be used.

– FC = 0x73

– P0 = NAS Uplink COUNT value

– L0 = length of NAS Uplink COUNT value (i.e. 0x00 0x04)

The input key KEY shall be K_AMF.

A.14.2 Handover

This input string is used when there is a need to derive K_ASME‘ from K_AMF during mapping of security contexts from 5G to EPS at handovers. The following input parameters shall be used.

– FC = 0x74

– P0 = NAS Downlink COUNT value

– L0 = length of NAS Downlink COUNT value (i.e. 0x00 0x04)

The input key KEY shall be K_AMF.