A.3 Calculation of PTK

33.3033GPPProximity-based services (ProSe)Release 17Security aspectsTS

When calculating a PTK from PGK, the following parameters shall be used to form the input S to the KDF that is specified in Annex B of TS 33.220 [5]:

– FC = 0x4A.

– P0 = Group Member Identity (i.e. the Layer 2 source address of the sending UE).

– L0 = length of Group Member Identity ( i.e. 0x00 0x03).

– P1 = PTK Identity.

– L1 = length of PTK Identity (i.e. 0x00 0x02).

– P2 = Group Identity.

– L2 = length of Group Identity (i.e. 0x00 0x03).

The input key shall be the 256-bit PGK.