protected function hashIt(/*# string */ $key)/*# : string */
    {
        $md5  = md5($key);
        $hash = $this->file_pref . $md5 . $this->file_suff;

        // no hash
        if (!$this->hash_level) {
            return $hash;
        }

        // hash
        $pref = '';
        for ($i = 0; $i < $this->hash_level; $i++) {
            $pref .= $md5[$i] . '/';
        }
        return $pref . $hash;
    }