18.9.11.2.15 Ensure 'Require additional authentication at startup: Configure TPM startup key:' is set to 'Enabled: Do not allow startup key with TPM'

Information

This policy setting allows you to configure whether BitLocker requires additional authentication each time the computer starts. This policy setting is applied when you turn on BitLocker.

Note: Only one of the additional authentication options can be required at startup, otherwise a policy error occurs.

On a computer with a compatible TPM, four types of authentication methods can be used at startup to provide added protection for encrypted data. When the computer starts, it can use only the TPM for authentication, or it can also require insertion of a USB flash drive containing a startup key, the entry of a 4-digit to 20-digit personal identification number (PIN), or both.

Note #2: If you want to require the use of a startup PIN and a USB flash drive, you must configure BitLocker settings using the command-line tool manage-bde instead of the BitLocker Drive Encryption setup wizard.

The recommended state for this setting is: Enabled: Do not allow startup key with TPM.

Rationale:

TPM without use of a PIN will only validate early boot components and does not require a user to enter any additional authentication information. If a computer is lost or stolen in this configuration, BitLocker will not provide any additional measure of protection beyond what is provided by native Windows authentication unless the early boot components are tampered with or the encrypted drive is removed from the machine.

Solution

To establish the recommended configuration via GP, set the following UI path to Enabled: Do not allow startup key with TPM:

Computer Configuration\Policies\Administrative Templates\Windows Components\BitLocker Drive Encryption\Operating System Drives\Require additional authentication at startup: Configure TPM startup key:

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 7 & Server 2008 R2 Administrative Templates (or newer).

Impact:

A TPM and a startup key will not be a permitted combination for BitLocker authentication.

Default Value:

Allow startup key with TPM. (A TPM can be used in conjunction with a startup key.)

See Also

https://workbench.cisecurity.org/files/2700

Item Details

Category: IDENTIFICATION AND AUTHENTICATION, SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|IA-5c., 800-53|SC-28(1), CSCv6|13.2, CSCv6|16.11

Plugin: Windows

Control ID: 740ce667be37d52f126693d2ebde73c33547b6130fe3ccf0b1f9dad35c2c3792