When does BitLocker unlocks auto-unlockable disks?

4

Sorry for the tongue-twister in the title :)

I have 2 hard disks, one small and fast (system) and other big and slow (data), both fixed. I want to have both of them fully encrypted, and for that purpose I used Windows 8.1 and BitLocker.

I want the data disk being unlocked automatically, so I unlock it once manually and check the "automatically unlock" checkbox. After that, it unlocks automatically when booting. Great!

My question now is: when does this happens in the boot process? I've read Microsoft documentation saying that it happens "when you logon", but that is not very specific. Does it happen before booting Windows? Does it happen after being logged in?

The motivation behind this question is that I want to make some symbolic links from the small disk to the big one so I can save some space in rarely used folders, and the fact that the big disk might not be available until some unknown point in time could be a problem.

MM.

Posted 2014-02-10T11:08:48.407

Reputation: 317

Answers

4

You mentioned the answer in your post already;

I've read Microsoft documentation saying that it happens "when you logon", but that is not very specific. Does it happen before booting Windows? Does it happen after being logged in?

This is actually very specific, assuming your computer is passworded, after you have entered your password and 'logged in', the drive will unlock.

Relevant information from the Microsoft Support document for Bitlocker:

Automatically unlock. Fixed data drives encrypted with BitLocker . Automatic unlocking for removable data drives can be selected after the drive is encrypted. To be able to automatically unlock fixed data drives, the drive that Windows is installed on must also be encrypted by BitLocker.

Source:
http://windows.microsoft.com/en-nz/windows7/learn-more-about-bitlocker-drive-encryption

Michael Frank

Posted 2014-02-10T11:08:48.407

Reputation: 7 412

I was hoping that phrasing was only a simplification. But I just tested it: if you configure a drive to auto-unlock and then reboot into another user account, it's locked. So when you logon is very specific, yup. Maybe there is a way to unlock both disks at the same time? – MM. – 2014-02-10T11:20:22.897

Assuming they're both set to auto-unlock, they should both unlock when you log in. Are they locked to different accounts? Or is the second drive only unlocking when you attempt to access it? – Michael Frank – 2014-02-10T11:22:10.117

Nah, this would be a one-user-only machine. I just created another user to test the theory. To summarize: I'd like to enter 1 password on pre-boot authentication and N disks (1 system + N data) to be unlocked automatically before Windows boots (or at least very early, before actual logon happens). – MM. – 2014-02-10T11:29:34.233

You might be able to achieve that with the PIN authentication mode, it requires you to enter a PIN after POST. You will need a TPM module to activate this method. Alternatively, you could use a USB key as authentication. This method is obviously more prone to accidentally locking yourself out due to a misplaced USB. – Michael Frank – 2014-02-10T11:40:10.940

Asked: 2014-02-10T11:08:48.407

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Active: 2014-02-10T11:14:09.473