This policy setting specifies the constraints for passwords used to unlock BitLocker-protected operating system drives. Note: This setting is enforced when turning on BitLocker, not when unlocking a volume. BitLocker will allow unlocking a drive with any of the protectors available on the drive. The recommended state for this setting is: Disabled. Rationale: Using a dictionary-style attack, passwords can be guessed or discovered by repeatedly attempting to unlock a drive. Since this type of BitLocker password does include anti-dictionary attack protections provided by a TPM, for example, there is no mechanism to slow down rapid brute-force attacks against them.
Solution
To establish the recommended configuration via GP, set the following UI path to Disabled: Computer Configuration\Policies\Administrative Templates\Windows Components\BitLocker Drive Encryption\Operating System Drives\Configure use of passwords for operating system drives Note: This Group Policy path may not exist by default. It is provided by the Group Policy template VolumeEncryption.admx/adml that is included with the Microsoft Windows 8.0 & Server 2012 (non-R2) Administrative Templates (or newer). Impact: The password option will not be available when configuring BitLocker for the operating system drive. Default Value: Passwords are supported, without complexity requirements and with an 8 character minimum.