PCI-DSS Full Disk Encryption Part 1

In PCI-DSS, one of the most difficult requirement to get through would be Requirement 3, that deals with stored credit card information and how to protect it. Aside from Requirement 10: Logging and Requirement 6: Software, Requirement 3: Storage makes up a bulk of the remediation effort and cost of PCI-DSS.

The excerpt ominously states at the beginning: Protection methods such as encryption, truncation, masking, and hashing are critical components of cardholder data protection. If an intruder circumvents other security controls and gains access to encrypted data, without the proper cryptographic keys, the data is unreadable and unusable to that person. Other effective methods of protecting stored data should also be considered as potential risk mitigation opportunities. For example, methods for minimizing risk include not storing cardholder data unless absolutely necessary, truncating cardholder data if full PAN is not needed, and not sending unprotected PANs using end-user messaging technologies, such as e-mail and instant messaging.

It goes without saying that if you have credit card information on file for whatever reason, it would be a good time to relook at the necessity of it. If you don’t need it, get rid of it, because the cost of maintenance and remediation may not be worth whatever value you think you are obtaining from storage of card data.

If you do need it, well, PCI provides a few options for you to protect it: Encryption, Truncation, Masking and Hashing. In this series of articles we will be looking into encryption and more specifically Full Disk Encryption.

Encryption itself deserves a long drawn out discussion and the types of encryption – you have applications doing encryption through the application library, you have database encryption like TDE, you have file encryption or folder encryption, you have full disk encryption. One part is the encryption methodology. The other part of it is the encryption key management. The latter is the one that usually throws up a headache.

We will be exploring Full Disk Encryption or FDE, and where it can be implemented to comply to PCI-DSS.

There is a specific part in 3.4.1 stating:

If disk encryption is used (rather than file- or column-level database encryption), logical access must be managed separately and independently of native operating system authentication and access control mechanisms (for example, by not using local user account databases or general network login credentials). Decryption keys must not be associated with user accounts.

So aside from the encryption being strong encryption and key management being done properly, PCI says, there are a few more things to be aware of for full disk encryption:

a) Logical access must be separate and independent of the native OS authentication

b) Decryption key must not be associated with the user account.

What does this mean?

Let’s look at Bitlocker for now, since that’s everyone’s favourite example.

Bitlocker has gone through a lot of stick probably because it’s a native Microsoft offering. Maybe. I don’t know. The fact is Bitlocker is able to use 128 or 256 bit AES so basically, in terms of strong cryptography, it’s possible. It’s the key management that’s the issue.

For key management, the recommended usage with Bitlocker is to use the Trusted Platform Module version 1.2 or later. The TPM is a hardware in your server that somewhat acts like a key vault or key management module, to simplify it. It offers system verification to ensure there is no tampering of the system at startup. Beginning with Windows 10, version 1803, you can check TPM status in Windows Defender Security Center > Device Security > Security processor details. In previous versions of Windows, open the TPM MMC console (tpm.msc) and look under the Status heading.

Bitlocker can also be used without TPM, although that means the system integrity checks are bypassed. It can operate along with Active Directory, although the newer versions of bitlocker doesn’t store the password hash in AD anymore by default. Instead a recovery password can be stored in the AD if required.

With the TPM, it’s still not the end of it, because we need to make sure that there is a separation of authentication for bitlocker to operate. In this case we will look to configure it with a PIN (which essentially is a password that you know).

First of all, let’s see what at the end we should be seeing.

So at the end you are basically seeing both file systems being encrypted. I’ve been asked before if all volumes need to be encrypted, and the answer is no, because bitlocker can’t do that anyway. Your system drive can’t be encrypted. So for PCI, it makes sense NOT to store card data in drives that are not encrypted.

The next thing we need to check is to ensure your set up has fulfilled the strong encryption requirement of PCI-DSS:

So you have a few things to ensure that strong crypto is enabled and key protectors are in place. So what you have is bitlocker now enabled. You also basically need to ensure you properly document the key management policy – include in AES256 or 128 that you are using, which drives are protected, key expiry date.

Keep in mind also the following:

FVEK (Full Volume Encryption Key) as DEK and VMK (Volume Master Key) as KEK.

FVEK stores in Boot sector (Volume meta data) in hard disk and VMK stores in TPM chip PCR register (it’s a Hardware chip which place in Motherboard).

In general, the above would fulfill PCI requirements. In our next article, we will write out on how logical access to the encrypted file system can be separated from the native OS authentication mechanism.

Meantime, please drop us any enquiries at pcidss@pkfmalaysia.com if you need to know more about PCI-DSS or any compliance matters in IT. We are here to help!

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