B.3 NAF specific key derivation in GBA and GBA_U

33.2203GPPGeneric Authentication Architecture (GAA)Generic Bootstrapping Architecture (GBA)TS

In GBA and GBA_U, the input parameters for the key derivation function shall be the following:

– FC = 0x01,

– P1 = RAND,

– L1 = length of RAND is 16 octets (i.e. 0x00 0x10),

– P2 = IMPI encoded to an octet string using UTF-8 encoding (see clause B.2.1),

– L2 = length of IMPI is variable (not greater that 65535),

– P3 = NAF_ID with the FQDN part of the NAF_ID encoded to an octet string using UTF-8 encoding (see clause B.2.1), and

– L3 = length of NAF_ID is variable (not greater that 65535).

In the key derivation of Ks_NAF as specified in clause 4 and Ks_ext_NAF as specified in clause 5,

– P0 = "gba-me" (i.e. 0x67 0x62 0x61 0x2d 0x6d 0x65), and

– L0 = length of P0 is 6 octets (i.e., 0x00 0x06).

In the key derivation of Ks_int_NAF as specified in clause 5,

– P0 = "gba-u" (i.e. 0x67 0x62 0x61 0x2d 0x75), and

– L0 = length of P0 is 5 octets (i.e., 0x00 0x05).

The Key to be used in key derivation shall be:

– Ks (i.e. CK || IK concatenated) as specified in clauses 4 and 5,

NOTE: In the specification this function is denoted as:
Ks_NAF = KDF (Ks, "gba-me", RAND, IMPI, NAF_Id),
Ks_ext_NAF = KDF (Ks, "gba-me", RAND, IMPI, NAF_Id), and
Ks_int_NAF = KDF (Ks, "gba-u", RAND, IMPI, NAF_Id).