static public function getDefaultKeyName(Config $conf = null) {
        $locationId = "global";
        if (is_null($conf)) {
            $projectId = self::getProjectId();
            $keyRingId = self::getKeyRingId();
            $cryptoKeyId = self::getCryptoKeyId();
        } else {
            $projectId = $conf->get(self::CONF_PROJECT_ID_NAME);
            $keyRingId = $conf->get(self::CONF_KEYRING_ID_NAME);
            $cryptoKeyId = $conf->get(self::CONF_KEY_ID_NAME);
        }
        return self::getKeyName($projectId, $locationId, $keyRingId, $cryptoKeyId);
    }