AEF PSK key derivation shall be performed using the key derivation function (KDF) specified in TS 33.220. This subclause specifies how to construct the input string, S, to the KDF (which is input together with the relevant key). The FC number space is controlled by TS 33.220. AEF PSK shall be derived by the API invoker and the CAPIF core function based on Service API interface information and CAPIF-1e TLS session parameters. Length and format of TLS session parameters used for key derivation are as specified in TLS. Security profiles for TLS implementation and usage shall follow the provisions given in TS 33.310, Annex E. The following parameters shall be used to form the input S to the KDF. The input key shall be equal to CAPIF-1e TLS session's Master Secret.