This is a quick guide to implementing First Data, Aka. Linkpoint or Global Gateway as your payment processor in CiviCRM, unlike Authorize.net and Paypal, using First Data is slightly more complicated.
You will need to place a .PEM certificate in your file system and correctly point your CiviCRM to it, you will have to open port 1129 on your rever and/or firewall, and finally make sure that the url to the payment processor is correct.
First Data requires the placement of a .PEM Certificate within your server file structure.
While the .PEM Certificate may resemble an SSL Certificate, it has nothing to do with your standard SSL implementation. The .PEM only serves as a handshake authentication between your server and the payment processor.
You should place it in a folder where your standard php user has read access, but preferably somewhere outside your web directory (not visible to the outside word). The file is usually a ten digit integer with a .pem extension, and should be in ASCII format to be Linux readable.
Once the .pem certificate is placed in the directory, make sure you insert the full certificate path into your CiviCRM payment processor configuration, starting from server root all the way out to the file location and including the file name.
First Data requires TCP port 1129 to be opened bidirectionally.
On a Linux server you will likely have to modify your IP Tables, if you have root access to your server you can do this by using some of the quickguides.
If you don't have root access to your server you will need host modify the IP Tables for you.
by default the First Data payment processor will reside at https://secure.linkpt.net, make sure you have nothing after the .net (example of bad: https://secure.linkpt.net/)
(this guide is not complete yet, but I will keep working on it. Bdanza)