You should purchase your encrypting magnetic card reader from your gateway provider. It will be pre-programmed with the correct key and settings. Card readers need no software installation or reconfiguration. Just plug the reader into an available USB port.
NOTE FOR MAC USERS: For Mac users, do not do the keyboard identification process when you plug in your credit card reader. Cancel the process if you are prompted to identify a keyboard after plugging in the credit card reader. If you accidentally go through this process, go to settings and re-identify your keyboards. Press the Tab key. When asked to press the key next to the shift key, press Tab again. You will be able to clear the incorrect keyboard.