code: def encrypted_to(self, raw_data):
          
          # TODO: make this support multiple keys.
          result = self._gpg.list_packets(raw_data)
          if not result.key:
              raise LookupError(
                  "Content is not encrypted to a GnuPG key!")
          try:
              return self.find_key_by_keyid(result.key)
          except:
              return self.find_key_by_subkey(result.key)
docs: Return the key to which raw_data is encrypted to.