function serialize()
    {
        $data = array(
                     'version' => '2',
                     'handle' => $this->handle,
                     'secret' => base64_encode($this->secret),
                     'issued' => strval(intval($this->issued)),
                     'lifetime' => strval(intval($this->lifetime)),
                     'assoc_type' => $this->assoc_type
                     );

        assert(array_keys($data) == $this->assoc_keys);

        return Auth_OpenID_KVForm::fromArray($data);
    }