def authority_issuer_serial(self):
        """
        :return:
            None or a byte string of the SHA-256 hash of the isser from the
            authority key identifier extension concatenated with the ascii
            character ":", concatenated with the serial number from the
            authority key identifier extension as an ascii string
        """

        if self._authority_issuer_serial is False:
            akiv = self.authority_key_identifier_value
            if akiv and akiv['authority_cert_issuer'].native:
                issuer = self.authority_key_identifier_value['authority_cert_issuer'][0].chosen
                # We untag the element since it is tagged via being a choice from GeneralName
                issuer = issuer.untag()
                authority_serial = self.authority_key_identifier_value['authority_cert_serial_number'].native
                self._authority_issuer_serial = issuer.sha256 + b':' + str_cls(authority_serial).encode('ascii')
            else:
                self._authority_issuer_serial = None
        return self._authority_issuer_serial
def authority_issuer_serial ( self ) : if self . _authority_issuer_serial is False : akiv = self . authority_key_identifier_value if akiv and akiv [ 'authority_cert_issuer' ] . native : issuer = self . authority_key_identifier_value [ 'authority_cert_issuer' ] [ 0 ] . chosen issuer = issuer . untag ( ) authority_serial = self . authority_key_identifier_value [ 'authority_cert_serial_number' ] . native self . _authority_issuer_serial = issuer . sha256 + b':' + str_cls ( authority_serial ) . encode ( 'ascii' ) else : self . _authority_issuer_serial = None return self . _authority_issuer_serial
:return:
            None or a byte string of the SHA-256 hash of the isser from the
            authority key identifier extension concatenated with the ascii
            character ":", concatenated with the serial number from the
            authority key identifier extension as an ascii string