Active Directory and the Case of the Failed BitLocker Recovery Key Archive
This is an issue I came across this evening at home (yes, just to reiterate, home), however the issue applies equally to my workplace as we encounter the same issue there.
One of the laptops in my house incorporates a TPM Module which I take advantage of to BitLocker encrypt the hard disk and using the TPM and a PIN. This gives me peace of mind as it’s the laptop used by my wife who although doesn’t currently will likely start to take her device out on the road when studying at university.
Historically, I have used the Save to File method of storing the recovery key, storing the key both on our home server and on my SkyDrive account for protection, but as of our new Windows Server 2012 Essentials environment, I wanted to take advantage of Active Directory and configure the clients to automatically archive the keys to there.
The key to beginning this process is to download an .exe file from Microsoft (http://www.microsoft.com/en-us/download/details.aspx?id=13432). I’m not going to explain here how to extend the AD Schema or modify the domain ACL for this all to work as that is all explained in the Microsoft document.
Following the instructions, I created a GPO which applied both the Trusted Platform Module Services Computer Configuration Setting for Turn on TPM Backup to Active Directory Domain Services and also the setting for BitLocker Drive Encryption Store Computer Configuration Setting for Store BitLocker Recovery Information in Active Directory Domain Services.
After allowing the machine to pickup the GPO and a restart to be sure, I enabled BitLocker and I realised that after verification in AD, nothing was being backed up. Strange I thought, as this matches a problem in the office at work however we had attributed this problem at work to a potential issue with our AD security ACEs, but at home, this is a brand new Windows Server 2012 with previously untouched ACEs out of the OOBE.
After scratching my head a little and a bit more poking around in Group Policy, I clocked it. The settings defined in the documentation are for Windows Vista. Windows 7 and Windows 8 clients rely on a different set of Group Policy Computer Configuration settings.
These new settings give you far more granular control of BitLocker than the Windows Vista settings did, so much so, that Microsoft elected that the Windows Vista settings would simply not apply to WindowsÂ 7 or 8 and that the new settings needed to be used.
You can find the new settings in Computer Configuration > Administrative Tools > Windows Components > BitLocker Drive Encryption. The settings in the root of this GPO hive are the existing Vista settings. The new Windows 7 and Windows 8 settings live in the three child portions: Fixed, Operating System and Removable Drives.
Each area gives you specific, granular control over how BitLocker affects these volumes, including whether to store the key in AD DS, whether to allow a user to configure a PIN or just to use the TPM and probably the best option second to enabling ADÂ DS archive in my opinion is whether to allow the user to select or whether to mandate that the entire drive or only the used space is encrypted. The Operating System Drives portion gives you the most options and will likely be the one people want to configure most as this is ultimately what determines the behaviour when booting your computer.
I’mÂ sure you’ll agree that there’s a lot of new settings here over Vista and that this gives you much greater flexibility and control over the settings, but with great power comes great responsibility. Make sure you read the effects and impact of each setting clearly and that you test your configuration and if possible, backup any data on any machines which you are testing BitLocker GPOs against in the event that the key isn’t archived to AD DS and that you enter a situation where you need, but don’t have that recovery key available.