Cromulent wrote:
The question is really do I need to adhere to SAQ C or SAQ D? Originally I thought I'd need to adhere to SAQ D but I was lead to believe that SAQ C would be sufficient.
The primary question is what is happening with the cardholder data (and more specifically the PAN - Primary Account Number). PCI will apply to any system that stores, processes, or simply transmits the information.
If you're going to store the PAN, jump right to the full SAQ D, no question. It's the only SAQ level that permits electronic storage of card data.
If your systems are just processing or transmitting the PAN, you can use SAQ C.
If you're offloading the processing entirely (payment form hosted by other provider, or using a provider where you supply a form that posts to the providers servers so your servers never see card data) you should be able to get away with SAQ A, or maybe even justify your server being completely out of scope for PCI entirely if it never deals with card data. Though SAQ A is pretty trivial and deals with ensuring your processors are themselves compliant so probably better to have filled out.
As others have mentioned, doing the most you can to avoid storing card data is your best option. If not, I'd probably suggest that you dedicate a node solely for secure storage of the card data and no other function at all (e.g., implement your own version of the Braintree vault and avoid your main application stack from touching raw card data). My own opinion is that you won't quite be able to meet all the technical requirements of SAQ D (A/C is doable), but that's personal opinion, and PCI in general is self-certification, plus the downside risk is only on the back-end in terms of possible penalties in the event of a breach.
In any case, once a system is within PCI scope, any other accessible system that might have any chance or possibility of access to the network traffic or systems involved will also need to be compliant. In a default configuration that would probably include all other Linodes on the same local network, which is clearly impossible to control, so it's important that you carefully firewall everything (and/or draw encrypted boundaries with SSL) to avoid scope creep involving more machines than necessary or possible to address.
In addition to the other thread already referenced, here, an earlier one (
viewtopic.php?t=5622) may also be useful. Also, the PCI site (
http://www.pcisecuritystandards.org) is the main reference - the SAQ instructions and guidelines document can help in identifying which SAQ you need to meet.
-- David