code: def dummy_signatures(self):
          
          if not self.signing_algorithm:
              return []
          algo_id = {'sha1': 1, 'sha384': 2}[self.signing_algorithm]
          signature = make_dummy_signature(algo_id)
          return [(algo_id, signature)]
docs: Create a dummy signature.
  
          This is used when initially writing the MAR header and we don't know
          what the final signature data will be.
  
          Returns:
              Fake signature data suitable for writing to the header with
              .write_signatures()