def self_signed(self):
        """
        :return:
            A boolean - if the certificate is self-signed
        """

        if self._self_signed is None:
            self._self_signed = False
            if self.asn1.self_signed in set(['yes', 'maybe']):

                signature_algo = self.asn1['signature_algorithm'].signature_algo
                hash_algo = self.asn1['signature_algorithm'].hash_algo

                if signature_algo == 'rsassa_pkcs1v15':
                    verify_func = rsa_pkcs1v15_verify
                elif signature_algo == 'dsa':
                    verify_func = dsa_verify
                elif signature_algo == 'ecdsa':
                    verify_func = ecdsa_verify
                else:
                    raise OSError(pretty_message(
                        '''
                        Unable to verify the signature of the certificate since
                        it uses the unsupported algorithm %s
                        ''',
                        signature_algo
                    ))

                try:
                    verify_func(
                        self,
                        self.asn1['signature_value'].native,
                        self.asn1['tbs_certificate'].dump(),
                        hash_algo
                    )
                    self._self_signed = True
                except (SignatureError):
                    pass

        return self._self_signed
:return:
            A boolean - if the certificate is self-signed