how do i store some value to use after redirected from Payment gateway

Or save the info in an encrypted cookie.

can you please explain how can I use an encrypted cookie?

I tried using cookie but it is not working.

PHP Code:

helper('cookie');
 set_cookie('username', $data['billing_name'], time() + 60*60*24*30);
return redirect('testing'); exit; 


PHP Code:

public function testing(){
  helper('cookie');
  echo "page is working";
  echo get_cookie('username', false, '');
}