Question: In the Generic Bootstrapping Architecture (GBA) key derivation for Ks_NAF and Ks_ext_NAF, what is the specific value and length of the input parameter P0 used in the Key Derivation Function (KDF)?
Option 1: P0 = gba-u with a length of 5 octets (0x00 0x05)
Option 2: P0 = gba-me with a fixed length of 8 octets (0x00 0x08)
Option 3: P0 = gbau with a variable length not greater than 65535
Option 4: P0 = gba-me with a length of 6 octets (0x00 0x06)
Explanation: In the context of GBA key derivation for both Ks_NAF and Ks_ext_NAF, the input parameter P0 is specifically defined as the string gba-me. This string, when encoded, has a length of 6 octets (0x67 0x62 0x61 0x2d 0x6d 0x65), which corresponds to the hexadecimal representation of each character in gba-me. Thus, the correct specification for P0 in this scenario is gba-me with a length of 6 octets.