protected function getValidAlgorithm($class)
    {
        $logging = \Plop\Plop::getInstance();;
        $w =    'abcdefghijklmnopqrstuvwxyz' .
                'ABCDEFGHIJKLMNOPQRSTUVWXYZ' .
                '1234567890-@.';
        $name = $class::getName();
        if (!is_string($name) || strspn($name, $w) !== strlen($name)) {
            $logging->debug(
                'Skipping algorithm "%(name)s" (invalid algorithm name)',
                array('name' => $name)
            );
            return null;
        }
        return $name;
    }