docs: def _load_hardware_key(keyfile):
      """ Load a 256-bit key, similar to stored in efuse, from a file
  
      192-bit keys will be extended to 256-bit using the same algorithm used
      by hardware if 3/4 Coding Scheme is set.
      """
      key = keyfile.read()
      if len(key) not in [24, 32]:
          raise esptool.FatalError("Key file contains wrong length (%d bytes), 24 or 32 expected." % len(key))
      if len(key) == 24:
          key = key + key[8:16]
          print("Using 192-bit key (extended)")
      else:
          print("Using 256-bit key")
  
      assert len(key) == 32
      return key