code: def _set_signature_type(self):
          
          try:
              verify_interface(ec.EllipticCurve, self.algorithm.signing_algorithm_info)
              return ec.EllipticCurve
          except InterfaceNotImplemented:
              raise NotSupportedError("Unsupported signing algorithm info")
docs: Ensures that the algorithm signature type is a known type and sets a reference value.