code: def iter_chunks(self, start_count=0):
          
          ciphertext = self.chunks_block
          chunknum = start_count
          idx = 0
          lastchunk = False
          while idx < len(ciphertext):
              plainlen = int.from_bytes(ciphertext[idx: idx+4], 'little')
              chunklen = plainlen + 16
              if idx + 4 + chunklen == len(ciphertext):
                  lastchunk = True
              elif idx + chunklen > len(ciphertext):
                  raise ValueError("Bad ciphertext; when reading chunks, hit EOF early")
              yield chunknum, ciphertext[idx + 4 : idx + 4 + chunklen], lastchunk
              idx += chunklen + 4
              chunknum += 1
docs: Iterate over the chunks of the file according to their length prefixes.
          yields: index <int>, encrypted chunks without length prefixes <bytes>, lastchunk <bool>