protected function convertDN($dn)
    {
        $base64 = false;
        // ASCII-chars that are NOT safe for the
        // start and for being inside the dn.
        // These are the int values of those chars.
        $unsafe_init = array(0, 10, 13, 32, 58, 60);
        $unsafe      = array(0, 10, 13);

        // Test for illegal init char
        $init_ord = ord(substr($dn, 0, 1));
        if ($init_ord >= 127 || in_array($init_ord, $unsafe_init)) {
            $base64 = true;
        }

        // Test for illegal content char
        for ($i = 0; $i < strlen($dn); $i++) {
            $char = substr($dn, $i, 1);
            if (ord($char) >= 127 || in_array($init_ord, $unsafe)) {
                $base64 = true;
            }
        }

        // Test for ending space
        if (substr($dn, -1) == ' ') {
            $base64 = true;
        }

        // if converting is needed, do it
        return ($base64)? 'dn:: '.base64_encode($dn) : 'dn: '.$dn;
    }