php - How do I make a PayPal encrypted buy now button with custom fields?

Question

Is there a way that my PHP code can generate an encrypted BuyNow button that also includes custom fields and also implements an IPN URL and redirect page?

Answer 1

You don't have to encrypt. Simply take the 'custom' variable, and, among other things you might need to put in there, add a hash of the price and product number, like so:

$sCustom .= '|' . md5($sSalt . $sProduct . $sPrice);

Then, when the IPN is processed, ensure that this hash was not disturbed with what is received back. If it was, then block the transaction.