Return a list of DER coded X.509 public keys from the v3 signature block

def get_public_keys_der_v3(self):
        """
        Return a list of DER coded X.509 public keys from the v3 signature block
        """

        if self._v3_signing_data == None:
            self.parse_v3_signing_block()

        public_keys = []

        for signer in self._v3_signing_data:
            public_keys.append(signer.public_key)

        return public_keys