Would implementing openssl prevent users from changing the button values?

Would implementing openssl prevent users from changing the button values? I've researched into encrypting buttons, from hosted to using openssl. Using hosted buttons would provide security at the cost of flexibility although there are variables that you can override, but still you cant override the important ones.

1. would using and implementing openssl on my webserver prevent users from changing a non-hosted paypal button ?

2. or would it just be better t开发者_StackOverflow中文版o fall back to a hosted button and use/validate using IPN?

My answer is non–PayPal specific (applies to any kind of HTTP form input), but the short answer is no. Even SSL cannot prevent the browser from modifying the form values that it receives.

A user could use a bookmarklet to execute a JavaScript program of her choice on your page after it has loaded, which has the ability to change form values. Because SSL only protects the transport between the browser and the server, not after the page has been processed by the browser, it makes no difference at all whether you use it.

This could be automated with Greasemonkey, which is the same idea, except makes it even easier for users to install other people’s JavaScript programs to run on your web page. As above, using SSL does not affect this at all, because it is all execute client side, which you, as the server, have no control over.

As you alluded to, using encrypted PayPal buttons would solve the problem, as any modification of the button parameters would invalidate the checksum, and PayPal would not accept the item.

The best solution would be using Express Checkout. This allows you a great deal more flexibility than standard buttons can ever offer you.

If you're thinking if doing IPN, you're probably capable enough to integrate Express Checkout. All it really is, is 1 API call, followed by a redirect to PayPal, and a minimum of 1 more API call to finalize the payment.

A typical flow would look as follows:

1. Call the SetExpressCheckout API. If you're new to this, it's made dead-easy with PayPal's NVP API interface. You can just send the data as a GET NVP string to https://api-3t.paypal.com/nvp and get a response back in the same format.
2. Take the token from the response, and redirect to https://www.paypal.com/cgi-bin/webscr?cmd=_express-checkout&token=XXXXXXX (https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_express-checkout&token=XXXXXXX for Sandbox testing)
3. As soon as the buyer is returned, PayPal will append a PAYERID to your RETURNURL. If you can't find it, call the GetExpressCheckoutDetails API and supply your token to retrieve it.
4. With the PAYERID and TOKEN, call DoExpressCheckoutPayment to finalize the payment.

To get started with this, I'd suggest taking a looking at the PHP NVP SDK they offer at https://www.x.com/community/ppx/sdks#NVP