private function encodeCookie($string)
{
$result = '';
$strlen = strlen($string);
for ($i = 0; $i < $strlen; ++$i) {
$char = substr($string, $i, 1);
$keychar = substr($this->cookie_key, $i % 32 - 1, 1);
$result .= chr(ord($char) + ord($keychar));
}
return $this->base64Encode($result);
}