Don’t display last username if C drive encrypted with BitLocker

I’m moving from encrypting laptops with a third party disk encryption product to BitLocker. The third party product uses a pre-boot username & password prompt, and only boots into Windows if the credentials are correct. Users then have to log on to Windows using the Active Directory credentials. The last username is remembered so they just type in their AD password and the desktop loads.

With BitLocker I’m using the Trusted Platform Module (TPM) in the laptops to tie the disk to the laptop, rather than giving users and extra set of credentials to remember. When they turn on, BitLocker checks the TPM and the laptop hardware for changes, and if all is normal Windows will boot and present the user with the logon screen. However, currently this means that a lost or stolen laptop will boot and display the name of the last user, which I don’t want. If the username isn’t displayed, there are now two pieces of information required to get past the Windows Logon screen.

I’ve achieved this using a Group Policy Preference, targeted with a WMI query. The GPPref sets the dontdisplaylastusername policy registry value if the C: drive is encrypted, or removes the value if the drive is not encrypted – i.e. during the transition phase, users with the old disk encryption won’t be forced to type in their AD username at the Windows logon screen, they’ll still be remembered from their previous logon.

The configuration is as follows:
Computer Configuration – Preferences – Windows Settings – Registry
General tab:

Action: Replace
Key Path: SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
Value: dontdisplaylastusername
Value type: REG_DWORD
Value Data: 00000001

Common tab:

Remove this item when it is no longer applied: ticked
Item-level targeting: ticked

WMI query:

Query: select IsVolumeInitializedForProtection from Win32_EncryptableVolume where DriveLetter = 'C:' and IsVolumeInitializedForProtection = True
Namespace: root\CIMv2\Security\MicrosoftVolumeEncryption
Property: IsVolumeInitializedForProtection
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