Storing credit card information securely and legally is very difficult and should not be attempted. I have no intention of storing credit card data but I'm dying to figure out the following:
My credit card info is being stored on a server some where in the world. This data is (hopefully) not being stored on a merchant's server, but at some point it needs to be stored to verify and charge the account identified by merchant submitted data.
My question is this: if you were tasked with storing credit card data what encryption strategy would you use to secure the data on-disk? From what I can tell submitted credit card info is being checked more or less in real time. I doubt that any encryption key used to secure the data is being entered manually, so decryption is being done on the fly, which implies that the keys themselves are being stored on-disk. How would you secure your data and your keys in an automated system like this?
Best Answer
If I was storing the number, I would be a giant service provider with a massive database. That database is spread across a highly-redundant storage array consisting of multiple cabinets, in separate rooms or ideally in separate geographical locations, connected by a SAN. My biggest insider threat is the distributed physical plant, the constant stream of worn-out drives, and several daily shifts of technicians, administrators, and engineers. It's a huge threat.
Therefore I would encrypt the data on a physically-isolated computer that connects to the mass storage over a network. The software would be as simple as possible: encryption and number verification. The public interfaces and business logic goes elsewhere. Accesses would be logged to a separate SAN.
Encrypt with something like AES. The raw AES key is only ever stored in RAM. The key is wrapped in a PGP file for each administrator, who has their own passphrase to enable the server. Less-trusted personnel can be given partial passphrases to use in disaster recovery, or passphrases can be stored in a vault somewhere. For encryption, pick a unique initialization vector (IV) for each card number, AES-encrypt the number using that IV, and store the IV and encrypted number to the SAN. Decryption only occurs using a privileged client interface; normal client connections used for purchases can never get a decryption.