A.17 SoR-MAC-I_AUSF generation function

33.5013GPPRelease 18Security architecture and procedures for 5G SystemTS

When deriving a SoR-MAC-I_AUSF from K_AUSF, the following parameters shall be used to form the input S to the KDF.

– FC = 0x77,

– P0 = SoR header,

– L0 = length of SoR header,

– P1 = Counter_SoR,

– L1 = length of Counter_SoR,

– P2 = octets included in SoR transparent container (in clause 9.11.3.51 of TS 24.501 [35]) beyond (and not including) octet 22,

– L2 = length of list data included in P2

The input key KEY shall be K_AUSF.

The selection of parameters included in P2 shall be the same as the selection of input to the Nausf_SoRProtection service operation. If none of these parameters are included in Nausf_SoRProtection service operation, P2 and L2 are not included for SoR-MAC-I_AUSF generation.

The SOR header is either received from the requester NF (e.g UDM), or constructed by the AUSF, as described in clause 9.11.3.51 of TS 24.501 [35], based on the information received from the requester NF (e.g. UDM), i.e. ACK Indication and List of preferred PLMN/access technology combinations or secured packet (if provided).

The SoR-MAC-I_AUSF is identified with the 128 least significant bits of the output of the KDF.