Authorize.net Advanced Integration Method 

The Advanced Integration Method is the recommended connection method and offers the most secure and flexible integration. AIM allows merchants to host their own secure payment form and send transactions to the payment gateway using an end-to-end secure sockets layer (SSL) connection.

* Employs industry standard secure data encryption technology - 128-bit Secure Sockets Layer (SSL) protocol.
* Uses transaction key authentication for ultimate security.
* Allows control over all phases of the customer's online transaction experience.
* Configurable transaction response integrates easily with merchant applications.

Authorize.net Simple Integration Method 

The Simple Integration Method uses scripting techniques to authenticate transactions with a unique transaction fingerprint. SIM provides a customizable, secure hosted payment form to make integration easy for Web merchants that do not have an SSL certificate. The Authorize.net Payment Gateway can handle all the steps in the secure transaction process - payment data collection, data submission and the response to the customer - while keeping Authorize.Net virtually transparent.

* Payment gateway hosted payment form employs 128-bit SSL data encryption.
* Digital fingerprints enhance security, providing multiple layers of authentication.
* Customize the look and feel of the payment gateway hosted payment form and/or receipt page.

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