code: def unwrap_message(self, message, signature):
          
          if not self.is_established:
              raise Exception("Context has not been established")
          if self._wrapper is None:
              raise Exception("Neither sealing or signing have been negotiated")
          else:
              return self._wrapper.unwrap(message, signature)
docs: Verifies the supplied signature against the message and decrypts the message if 'confidentiality' was
          negotiated.
          A SignatureException is raised if the signature cannot be parsed or the version is unsupported
          A SequenceException is raised if the sequence number in the signature is incorrect
          A ChecksumException is raised if the in the signature checksum is invalid
          :return: The decrypted message