Disk Encryption

[spetreski]

I have a question in regards to point 3.4.1 from the PCI Req. It clearly states that Window's EFS cannot be used as a disk encryption solution, however I have a hard time determining if Vista's Bitlocker (full disk encryption) can be used. Any thoughts?

[admin]

Requirement 3.4 in the SAP v1.1 does lead one to believe that EFS is not allowed, but there are compensating controls that could permit the secure use of EFS.

Imaging the intent is to prevent an attacker from gaining access to a user account that can then be used to decrypt the data. If EFS is used with Syskey 1 then req. 3.4 is correct. If instead, Syskey 2 or 3 are used, these could be compensating controls.

Look to the intent when interpreting the requirements.

[jbhall56]

Remember that with EFS Syskey 3 mode, the floppy disk CANNOT just be left in the machine. It must be removed and secured and only reinserted when the system needs to be booted. Syskey 3 is probably the best method as the operator or sys admin does not have to know the value of the Syskey as it is on the floppy disk. Unfortunately, most servers today do not have floppy drives and I'm not sure if Microsoft supports Syskey 3 on a CD-ROM.

The key to the encryption issue is whether the encryption is whole disk encryption or is it implemented at the folder level? If the encryption is whole disk, then the encryption is really only in place when the system is turned off because it must be decrypted in order for the system run. As I understand it, Bitlocker is a whole disk encryption technology, so once a user is logged on, the disk is available for access. So, if an attacker gains access to a system with whole disk encryption, the data is available. Hence why EFS and other whole disk encryption schemes are NOT acceptable to meet the requirements of 3.4.

Now with EFS encrypting at the folder level using Syskey 2 or 3, that is a different story. Not only does the user have to have rights to the folder, they must also have access to the key. Since using Syskey 2 and 3 means that the key is not on the system (unless someone left the floppy in the system), any attacker that compromises the system still needs access rights and the key to decrypt. Even if they have rights, without the key the data remains encrypted.

In my experience, it is very rare to see EFS implemented at the folder level. It's even more rare to see Syskey 2 or 3 implemented.

[admin]

What about Windows BitLocker Drive Encryption? Has anyone taken a look at that?

[jbhall56]

The rule of thumb to use, as it relates to PCI, is, whole disk encryption "bad," folder/file encryption "good."

The reason is that whole disk encryption, meaning the entire hard drive is encrypted with a key, is "bad" is that it only protects the system when it is powered off. Once a user powers up a system, the passphrase MUST be entered in order to get the system to boot. Once booted, the encryption is no longer protecting the data.

Folder, file or table column encryption are "good" because any user accessing the data MUST supply their passphrase in order to gain access to the encrypted data. The data is not unencrypted just because the system is running.

So, using these definitions, since BitLocker is a whole disk encryption system, it will not satisfy the PCI requirements.

This is not to say that EFS in whole disk mode, BitLocker, PGP or other whole disk encryption systems are bad and do not protect data. They are good solutions for protecting data on mobile devices when they are powered down. It's just that they do not satisfy the PCI encryption requirements because they are not enforced when the system is running.