code: def verify_signature(self):
          
          if self.get_contact_key:
              sender_key = self.get_contact_key(self.sender_handle)
          else:
              sender_key = fetch_public_key(self.sender_handle)
          if not sender_key:
              raise NoSenderKeyFoundError("Could not find a sender contact to retrieve key")
          MagicEnvelope(doc=self.doc, public_key=sender_key, verify=True)
docs: Verify the signed XML elements to have confidence that the claimed
          author did actually generate this message.