Question: What is the length of RAND used to derive RES* and XRES*?
Option 1: Variable length between 0x00 0x04 and 0x00 0x10
Option 2: Fixed length of 0x00 0x08
Option 3: Fixed length of 0x00 0x10
Option 4: Variable length as specified in 24.501 [35]
Explanation: According to the specification, when deriving RES* and XRES*, the length of RAND (L1) is fixed at 0x00 0x10, which corresponds to 16 bytes or 128 bits.