osCommerce PayPal IPN Module v1.0 For 2.2MS2
 
This module stores orders prematurely in the database to be processed by PayPal IPN notifications. This takes care of customers not returning back to the store to store the order in the database, and allows processing to occur when the PayPal IPN notification is received.

When communicating with the IPN notification, the order information is sent back to PayPal in a secure manner through PHP native OpenSSL capabilities or through cURL when OpenSSL is not available, or through a normal unsecure manner when no secure communication means exists, to confirm the order made. If the result is successful, the order status is updated automatically to show a successful order has been made. Invalid orders are left alone for the store administrator to verify.

This module also has OpenSSL public/private key encryption capabilities to securely send the order information to PayPal during the checkout procedure.

More information about this feature can be read here:

Encrypted Web Payments: https://www.paypal.com/us/cgi-bin/webscr?cmd=p/xcl/rec/ewp-intro-outside

This module was built to be as simple as possible without having the need to touch core codebase files or database changes for installation and usage.

* You can download the contribution from oscommerce.com for free