BitLocker Drive Encryption in Windows 7: Frequently Asked Questions

Articolo
09/12/2012

Applies To: Windows 7

BitLocker Drive Encryption is a data protection feature available in Windows 7 Enterprise, Windows 7 Ultimate, and in all editions of Windows Server 2008 R2. This topic includes frequently asked questions about BitLocker in Windows 7. For frequently asked questions about BitLocker in Windows Vista, see Windows BitLocker Drive Encryption Frequently Asked Questions.

Overview and requirements

What is BitLocker? How does it work?
Does BitLocker support multifactor authentication?
What are the BitLocker hardware and software requirements?
Why are two partitions required? Why does the system drive have to be so large?
Which Trusted Platform Modules (TPMs) does BitLocker support?
How can I tell whether my computer has a TPM version 1.2?
Can I use BitLocker on an operating system drive without a TPM version 1.2?
How do I obtain BIOS support for the TPM on my computer?
What credentials are required to use BitLocker?

Upgrading

What versions of Windows 7 include BitLocker? Can I use BitLocker on a Windows XP–based computer?
Can I upgrade my Windows XP–based computer to Windows 7 with the necessary disk configuration for BitLocker?
Can I upgrade my Windows Vista–based computer to Windows 7 with BitLocker enabled?
What is the difference between disabling, suspending, and decrypting when I turn off BitLocker?
Do I have to decrypt my BitLocker-protected drive to download and install system updates and upgrades?

Deployment and administration

Can BitLocker deployment be automated in an enterprise environment?
Can BitLocker encrypt more than just the operating system drive?
Is there a noticeable performance impact when BitLocker is enabled on a Windows 7–based computer?
Approximately how long will initial encryption take when BitLocker is turned on?
What happens if the computer is turned off during encryption or decryption?
Why does it appear that most of the free space in my drive is used when BitLocker is converting the drive?
Does BitLocker encrypt and decrypt the entire drive all at once when reading and writing data?
How can I prevent users on a network from storing data on an unencrypted drive?
What system changes would cause the integrity check on my operating system drive to fail?
What causes BitLocker to start into recovery mode when attempting to start the operating system drive?
Can I swap hard disks on the same computer if BitLocker is enabled on the operating system drive?
Can I access my BitLocker-protected drive if I insert the hard disk into a different computer?
Can I dual boot Windows 7 and Windows Vista with BitLocker-protected operating system drives?
Why is "Turn BitLocker on" not available when I right-click a drive?
What type of disk configurations are supported by BitLocker?
What if my disk configuration is not listed?

Key management

What is the difference between a TPM owner password, recovery password, recovery key, PIN, enhanced PIN, and startup key?
How can the recovery password and recovery key be stored?
Is it possible to add an additional method of authentication without decrypting the drive if I only have the TPM authentication method enabled?
If I lose my recovery information, will the BitLocker-protected data be unrecoverable?
Can the USB flash drive that is used as the startup key also be used to store the recovery key?
Can I save the startup key on multiple USB flash drives?
Can I save multiple (different) startup keys on the same USB flash drive?
Can I generate multiple (different) startup keys for the same computer?
Can I generate multiple PIN combinations?
What encryption keys are used in BitLocker? How do they work together?
Where are the encryption keys stored?
Why do I have to use the function keys to enter the PIN or the 48-character recovery password?
How does BitLocker help prevent an attacker from discovering the PIN that unlocks my operating system drive?
How can I evaluate a TPM's dictionary attack mitigation mechanism?
Can PIN length and complexity be managed with Group Policy?
How are the PIN and TPM used to derive the volume master key?

BitLocker To Go

What is BitLocker To Go?
How can I authenticate or unlock my removable data drive?
Can I use BitLocker To Go with computers running Windows XP or Windows Vista?
What happens if I try to open a BitLocker-protected, NTFS-formatted removable drive by using a computer running Windows XP or Windows Vista?
Is there a way to ensure the BitLocker To Go Reader is not installed on FAT-formatted drives?
Can I save files to my BitLocker-protected removable drive when I am using Windows XP or Windows Vista?
Can I download a copy of the BitLocker To Go Reader?
Why am I unable to access my removable drive on computers running Windows XP or Windows Vista when using the BitLocker To Go Reader?

Active Directory Domain Services (AD DS)

Important

For detailed instructions about how to configure AD DS for BitLocker, see Backing Up BitLocker and TPM Recovery Information to AD DS.

Does BitLocker require a schema extension to store recovery information in AD DS?
What type of information is stored in AD DS?
Does BitLocker encrypt recovery information as it is sent to AD DS?
Is the BitLocker recovery information stored in plaintext in AD DS?
What if BitLocker is enabled on a computer before the computer has joined the domain?
Is there an event log entry recorded on the client computer to indicate the success or failure of the Active Directory backup?
If I change the BitLocker recovery password on my computer and store the new password in AD DS, will AD DS overwrite the old password?
What happens if the backup initially fails? Will BitLocker retry the backup?

Security

What form of encryption does BitLocker use? Is it configurable?
What is the Diffuser?
What is best practice for using BitLocker on an operating system drive?
What are the implications of using the sleep or hibernate power management options?
What are the advantages of a TPM?
Is Microsoft pursuing any security certification for BitLocker?

Overview and requirements

What is BitLocker? How does it work?

BitLocker Drive Encryption is a data protection feature available in Windows 7 Enterprise and Windows 7 Ultimate for client computers and in Windows Server 2008 R2. BitLocker provides enhanced protection against data theft or exposure on computers and removable drives that are lost or stolen, and more secure data deletion when BitLocker-protected computers are decommissioned as it is much more difficult to recover deleted data from an encrypted drive than from a non-encrypted drive.

How BitLocker works with operating system drives

Data on a lost or stolen computer is vulnerable to unauthorized access, either by running a software attack tool against it or by transferring the computer's hard disk to a different computer. BitLocker helps mitigate unauthorized data access on lost or stolen computers by:

Encrypting the entire Windows operating system drive on the hard disk. BitLocker encrypts all user files and system files on the operating system drive, including the swap files and hibernation files.
Checking the integrity of early boot components and boot configuration data. On computers that have a Trusted Platform Module (TPM) version 1.2, BitLocker uses the enhanced security capabilities of the TPM to help ensure that your data is accessible only if the computer's boot components appear unaltered and the encrypted disk is located in the original computer.

BitLocker is integrated into Windows 7 and provides enterprises with enhanced data protection that is easy to manage and configure. For example, BitLocker can use an existing Active Directory Domain Services (AD DS) infrastructure to remotely store BitLocker recovery keys.

How BitLocker works with fixed and removable data drives

BitLocker can also be used to protect fixed and removable data drives. When used with data drives, BitLocker encrypts the entire contents of the drive and can be configured by using Group Policy to require that BitLocker be enabled on a drive before the computer can write data to the drive. BitLocker can be configured with the following unlock methods for data drives:

Automatic unlock. Fixed data drives can be set to automatically unlock on a computer where the operating system drive is encrypted. Removable data drives can be set to automatically unlock on a computer running Windows 7 after the password or smart card is initially used to unlock the drive. However, removable data drives must always have either a password or smart card unlock method in addition to the automatic unlock method.
Password. When users attempt to open a drive, they are prompted to enter their password before the drive will be unlocked. This method can be used with the BitLocker To Go Reader on computers running Windows Vista or Windows XP, to open BitLocker-protected drives as read-only.
Smart card. When users attempt to open a drive, they are prompted to insert their smart card before the drive will be unlocked.

A drive can support multiple unlock methods. For example, a removable data drive can be configured to be automatically unlocked on your primary work computer but query you for a password if used with another computer.

Does BitLocker support multifactor authentication?

Yes, BitLocker supports multifactor authentication for operating system drives. If you enable BitLocker on a computer that has a TPM version 1.2, you can use additional forms of authentication with the TPM protection. BitLocker offers the option to lock the normal boot process until the user supplies a personal identification number (PIN) or inserts a USB device (such as a flash drive) that contains a BitLocker startup key, or both the PIN and the USB device can be required. These additional security measures provide multifactor authentication and help ensure that the computer will not start or resume from hibernation until the correct authentication method is presented.

Note

Use of both the USB and PIN along with the TPM must be configured by using the Manage-bde command-line tool. This protection method cannot be specified by using the BitLocker setup wizard.

What are the BitLocker hardware and software requirements?

To use all BitLocker features, your computer must meet the hardware and software requirements listed in the following table.

BitLocker hardware and software requirements for operating system drives

Hardware configuration

The computer must meet the minimum requirements for Windows 7. For more information about Windows 7 requirements, see the Windows 7 Web site (https://go.microsoft.com/fwlink/?LinkID=155370).

Operating system

Windows 7 Ultimate, Windows 7 Enterprise, or Windows Server 2008 R2

Note
BitLocker is an optional feature of Windows Server 2008 R2. Use Server Manager to install BitLocker on a computer running Windows Server 2008 R2.

Hardware TPM

TPM version 1.2

A TPM is not required for BitLocker; however, only a computer with a TPM can provide the additional security of pre-startup system integrity verification and multifactor authentication.

BIOS configuration

A Trusted Computing Group (TCG)-compliant BIOS.
The BIOS must be set to start first from the hard disk, and not the USB or CD drives.
The BIOS must be able to read from a USB flash drive during startup.

File system

At least two NTFS disk partitions, one for the system drive and one for the operating system drive. The system drive partition must be at least 100 megabytes (MB) and set as the active partition.

BitLocker hardware and software requirements for data drives

File system

For a fixed or removable data drive to be BitLocker-protected, it must be formatted by using the exFAT, FAT16, FAT32, or NTFS file system.

Note
To use the BitLocker To Go Reader to read data on a removable data drive, the drive must be formatted by using the exFAT, FAT16, or FAT32 file system. If the drive is NTFS formatted, it can only be unlocked on a computer running Windows Server 2008 R2 or Windows 7 and previous versions of the Windows operating system will not recognize the drive and will prompt you to format the drive.

Drive size

The drive must be least 64 MB in size.

Why are two partitions required? Why does the system drive have to be so large?

Two partitions are required to run BitLocker because pre-startup authentication and system integrity verification must occur on a separate partition from the encrypted operating system drive. This configuration helps protect the operating system and the information in the encrypted drive. In Windows Vista, the system drive must be 1.5 gigabytes (GB), but in Windows 7 this requirement has been reduced to 100 MB for a default installation. The system drive may also be used to store the Windows Recovery Environment (Windows RE) and other files that may be specific to setup or upgrade programs. Computer manufacturers and enterprise customers can also store system tools or other recovery tools on this drive, which will increase the required size of the system drive. For example, using the system drive to store Windows RE along with the BitLocker startup file will increase the size of the system drive to 300 MB. The system drive is hidden by default and is not assigned a drive letter. The system drive is created automatically when Windows 7 is installed.

Which Trusted Platform Modules (TPMs) does BitLocker support?

BitLocker supports TPM version 1.2. BitLocker does not support previous versions of TPMs. Version 1.2 TPMs provide increased standardization, security enhancement, and improved functionality over previous versions. In addition, you must use a Microsoft-provided TPM driver. To check the TPM driver provider, click Start, type devmgmt.msc in the Search programs and files box, and then press ENTER to open Device Manager. Right-click the TPM, and click Properties. Click the Driver tab, and verify that the Driver Provider field displays Microsoft.

Important

When using BitLocker with a TPM, it is recommended that BitLocker be turned on immediately after the computer has been restarted. If the computer has resumed from sleep prior to turning on BitLocker, the TPM may incorrectly measure the pre-boot components on the computer. In this situation, when the user subsequently attempts to unlock the computer, the TPM verification check will fail and the computer will enter BitLocker recovery mode and prompt the user to provide recovery information before unlocking the drive.

How can I tell whether my computer has a TPM version 1.2?

Click Start, click Control Panel, click System and Security, click BitLocker Drive Encryption, and then click Turn On BitLocker. If your computer does not have a TPM version 1.2 or the BIOS is not compatible with the TPM, you will receive the following error message:

A compatible Trusted Platform Module (TPM) Security Device must be present on this computer, but a TPM was not found. Please contact your system administrator to enable BitLocker.

If you receive this error message on a computer that has a TPM, check if either of the following situations applies to your computer:

Some computers have TPMs that do not appear in the Windows 7 TPM Microsoft Management Console snap-in (tpm.msc) due to a BIOS setting that hides the TPM by default and does not make the TPM available unless it is first enabled in the BIOS. If your TPM might be hidden in the BIOS, consult the manufacturer's documentation for instructions to display or enable the TPM.
Some computers might have an earlier version of the TPM or an earlier version of the system BIOS that is not compatible with BitLocker. Contact the computer manufacturer to verify that the computer has a TPM version 1.2 or to get a BIOS update.

Can I use BitLocker on an operating system drive without a TPM version 1.2?

Yes, you can enable BitLocker on an operating system drive without a TPM version 1.2, if the BIOS has the ability to read from a USB flash drive in the boot environment. This is because BitLocker will not unlock the protected drive until BitLocker's own volume master key is first released by either the computer's TPM or by a USB flash drive containing the BitLocker startup key for that computer. However, computers without TPMs will not be able to use the system integrity verification that BitLocker can also provide.

To help determine whether a computer can read from a USB device during the boot process, use the BitLocker system check as part of the BitLocker setup process. This system check performs tests to confirm that the computer can properly read from the USB devices at the appropriate time and that the computer meets other BitLocker requirements.

To enable BitLocker on a computer without a TPM, you must enable the Require additional authentication at setup Group Policy setting, which is located in Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Operating System Drives. You must select the Allow BitLocker without a compatible TPM check box. After this setting is applied to the local computer, the non-TPM settings appear in the BitLocker setup wizard.

How do I obtain BIOS support for the TPM on my computer?

Contact the computer manufacturer to request a Trusted Computing Group (TCG)-compliant BIOS. Ensure that the BIOS meets the following requirements:

It is compatible with Windows 7 and has passed the Windows 7 logo tests.
It is compliant with the TCG standards for a client computer.
It has a secure update mechanism to help prevent a malicious BIOS from being installed on the computer.

What credentials are required to use BitLocker?

To turn on, turn off, or change configurations of BitLocker on operating system and fixed data drives, membership in the local Administrators group is required. Standard users can turn on, turn off, or change configurations of BitLocker on removable data drives. Disable the Control use of BitLocker on removable drives policy setting (located in Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Removable Data Drives) to restrict standard users from turning on or turning off BitLocker on removable data drives.

Upgrading

What versions of Windows 7 include BitLocker? Can I use BitLocker on a Windows XP–based computer?

BitLocker is available in Windows 7 Ultimate and Windows 7 Enterprise. However, you can unlock encrypted removable drives on any version of Windows 7. BitLocker is not available in Windows XP, but you can use the BitLocker To Go Reader to view content on BitLocker-protected removable drives from a computer running Windows XP.

Can I upgrade my Windows XP–based computer to Windows 7 with the necessary disk configuration for BitLocker?

Upgrading from Windows XP to Windows 7 is not supported. For information about how to migrate your files and folders to Windows 7, see Step-by-Step: Windows 7 Upgrade and Migration (https://go.microsoft.com/fwlink/?LinkId=159582). After you install Windows 7 Ultimate or Windows 7 Enterprise, your computer disk configuration supports BitLocker by default.

Can I upgrade my Windows Vista–based computer to Windows 7 with BitLocker enabled?

Yes. To upgrade from Windows Vista to Windows 7 without decrypting the operating system drive, open the BitLocker Drive Encryption Control Panel item in Windows Vista, click Turn Off BitLocker, and then and click Disable Protection. Disabling protection does not decrypt the drive; it disables the authentication mechanisms used by BitLocker and uses a clear key on the drive to enable access. Proceed with the upgrade process by using your Windows 7 DVD. After the upgrade has completed, open Windows Explorer, right-click the drive, and then click Resume Protection. This reapplies the BitLocker authentication methods and deletes the clear key.

What is the difference between disabling, suspending, and decrypting when I turn off BitLocker?

Decrypt completely removes BitLocker protection and fully decrypts the drive.

Disable and Suspend refer to the same process. Disable was used in Windows Vista, and Suspend is used in Windows 7. The term was changed to more accurately describe the process. When BitLocker is suspended, BitLocker keeps the data encrypted but encrypts the BitLocker volume master key with a clear key. The clear key is a cryptographic key stored unencrypted and unprotected on the disk drive. By storing this key unencrypted, the Suspend option allows for changes or upgrades to the computer without the time and cost of decrypting and re-encrypting the entire drive. After the changes are made and BitLocker is again enabled, BitLocker will reseal the encryption key to the new values of the measured components that changed as a part of the upgrade, and the clear key is erased. This option is only available for operating system drives.

Do I have to decrypt my BitLocker-protected drive to download and install system updates and upgrades?

Operating system upgrades from Windows Anytime Upgrade require that the operating system drive be decrypted prior to installation. If you upgrade from Windows Vista to Windows 7 or install other non-Microsoft updates, you might need to disable or suspend BitLocker so that a new measurement of the system can be taken after the upgrade or update has been applied. Software and operating system updates from Microsoft Update do not require drive decryption or that you disable or suspend BitLocker.

Note

Disable is the term used in Windows Vista to refer to the process of temporarily suspending BitLocker protection on a drive without decrypting the drive. In Windows 7, the term has been changed to Suspend to more accurately reflect the process.

Please refer to the following table to determine whether you must disable or suspend BitLocker or decrypt your drive before you perform an upgrade or update installation.

Type of update	Action
Windows Anytime Upgrade	Decrypt
Upgrade from Windows Vista to Windows 7	Disable
Non-Microsoft software updates, such as: Computer manufacturer firmware updates TPM firmware updates Non-Microsoft application updates that modify boot components	Suspend

Windows Anytime Upgrade

Decrypt

Upgrade from Windows Vista to Windows 7

Disable

Non-Microsoft software updates, such as:

Computer manufacturer firmware updates
TPM firmware updates
Non-Microsoft application updates that modify boot components

Suspend

If you disabled or suspended BitLocker, you can resume BitLocker protection after you have installed the upgrade or update. Upon resuming protection, BitLocker will reseal the encryption key to the new values of the measured components that changed as a part of the upgrade or update. If these types of upgrades or updates are applied without decrypting or disabling BitLocker, your computer will enter recovery mode when restarting and will require a recovery key or password to access the computer.

Deployment and administration

Can BitLocker deployment be automated in an enterprise environment?

Yes, you can automate the deployment and configuration of BitLocker with scripts that use the Windows Management Instrumentation (WMI) providers for BitLocker and TPM administration. How you choose to implement the scripts depends on your environment. You can also use the BitLocker command-line tool, Manage-bde.exe, to locally or remotely configure BitLocker. For additional information about writing scripts that use the BitLocker WMI providers, see the MSDN topic BitLocker Drive Encryption Provider (https://go.microsoft.com/fwlink/?LinkId=80600).

Can BitLocker encrypt more than just the operating system drive?

Yes. In Windows 7, BitLocker can encrypt operating system drives, fixed data drives, and removable data drives.

Is there a noticeable performance impact when BitLocker is enabled on a Windows 7–based computer?

Generally it imposes a single-digit percentage performance overhead.

Approximately how long will initial encryption take when BitLocker is turned on?

BitLocker encryption occurs in the background while you continue to work, and the system remains usable, but encryption times vary depending on the type of drive that is being encrypted, the size of the drive, and the speed of the drive. If you are encrypting very large drives, you may want to set encryption to occur during times when you will not be using the drive.

What happens if the computer is turned off during encryption or decryption?

If the computer is turned off or goes into hibernation, the BitLocker encryption and decryption process will resume where it stopped the next time Windows starts. This is true even if the power is suddenly unavailable.

Why does it appear that most of the free space in my drive is used when BitLocker is converting the drive?

BitLocker cannot ignore free space when the drive is being encrypted because unallocated disk space commonly contains data remnants. However, it is not efficient to encrypt free space on a drive. To solve this problem, BitLocker first creates a large placeholder file that takes most of the available disk space and then writes cryptographic material to disk sectors that belong to the placeholder file. During this process, BitLocker leaves 6 GB of available space for short-term system needs. All other space, including the 6 GB of free space not occupied by the placeholder file, is encrypted. When encryption of the drive is paused or completed, the placeholder file is deleted and the amount of available free space reverts to normal. A placeholder file is used only on drives formatted by using the NTFS or exFAT file system.

If you want to reclaim this free space before encryption of the drive has completed, you can use the Manage-bde command-line tool to pause encryption. To do this, open an elevated command prompt and type the following command, replacing driveletter with the letter of the drive you want to pause encryption on:

manage-bde –pause driveletter**:**

When you are ready to start encrypting the drive again, type the following command:

manage-bde –resume driveletter**:**

Does BitLocker encrypt and decrypt the entire drive all at once when reading and writing data?

No, BitLocker does not encrypt and decrypt the entire drive when reading and writing data. The encrypted sectors in the BitLocker-protected drive are decrypted only as they are requested from system read operations. Blocks that are written to the drive are encrypted before the system writes them to the physical disk. No unencrypted data is ever stored on a BitLocker-protected drive.

How can I prevent users on a network from storing data on an unencrypted drive?

In Windows 7, you can enable Group Policy settings to require that data drives be BitLocker-protected before a BitLocker-protected computer can write data to them. The policy settings you use for this are:

Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Fixed Data Drives\Deny write access to fixed drives not protected by BitLocker
Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Removable Data Drives\Deny write access to removable drives not protected by BitLocker

When these policy settings are enabled, the BitLocker-protected operating system will mount any data drives that are not protected by BitLocker as read-only.

If you are concerned that your users might inadvertently store data in an unencrypted drives while using a computer that does not have BitLocker enabled, use access control lists (ACLs) and Group Policy to configure access control for the drives or hide the drive letter.

For additional information about how to hide drive letters, see article 231289 in the Microsoft Knowledge Base (https://go.microsoft.com/fwlink/?LinkId=83219).

What system changes would cause the integrity check on my operating system drive to fail?

The following types of system changes can cause an integrity check failure and prevent the TPM from releasing the BitLocker key to decrypt the protected operating system drive:

Moving the BitLocker-protected drive into a new computer.
Installing a new motherboard with a new TPM.
Turning off, disabling, or clearing the TPM.
Changing any boot configuration settings.
Changing the BIOS, master boot record, boot sector, boot manager, option ROM, or other early boot components or boot configuration data.

This functionality is by design; BitLocker treats unauthorized modification of any of the early boot components as a potential attack and will place the system into recovery mode. Authorized administrators can update boot components without entering recovery mode by disabling BitLocker beforehand.

What causes BitLocker to start into recovery mode when attempting to start the operating system drive?

The following list provides examples of specific events that will cause BitLocker to enter recovery mode when attempting to start the operating system drive:

Changing any boot configuration data (BCD) boot entry data type settings with the exception of the following items:

DESCRIPTION

RAMDISKIMAGEOFFSET

PASSCOUNT

TESTMIX

FAILURECOUNT

TESTTOFAIL

Warning

When installing a language pack, an additional option in the language pack installation wizard asks if the user wants to apply language settings to All users and system accounts. If this option is selected, it will change the local computer BCD settings (if the user-only option is selected, BCD settings are not changed). This change will result in a modification of a BCD setting to the new locale value. If you are using a TPM with BitLocker, this is interpreted as a boot attack on reboot and the computer will require that the user enter the recovery password or recovery key to start the computer.
We recommend that you suspend BitLocker before changing locales or installing a language pack, just as you would before making any major computer configuration change, such as updating the BIOS.

Changing the BIOS boot order to boot another drive in advance of the hard drive.
Having the CD or DVD drive before the hard drive in the BIOS boot order and then inserting or removing a CD or DVD.
Failing to boot from a network drive before booting from the hard drive.
Docking or undocking a portable computer. In some instances (depending on the computer manufacturer and the BIOS), the docking condition of the portable computer is part of the system measurement and must be consistent to validate the system status and unlock BitLocker. This means that if a portable computer is connected to its docking station when BitLocker is turned on, then it might also need to be connected to the docking station when it is unlocked. Conversely, if a portable computer is not connected to its docking station when BitLocker is turned on, then it might need to be disconnected from the docking station when it is unlocked.
Changes to the NTFS partition table on the disk including creating, deleting, or resizing a primary partition.
Entering the personal identification number (PIN) incorrectly too many times so that the anti-hammering logic of the TPM is activated. Anti-hammering logic is software or hardware methods that increase the difficulty and cost of a brute force attack on a PIN by not accepting PIN entries until after a certain amount of time has passed.
Turning off the BIOS support for reading the USB device in the pre-boot environment if you are using USB-based keys instead of a TPM.
Turning off, disabling, deactivating, or clearing the TPM.
Upgrading critical early startup components, such as a BIOS upgrade, causing the BIOS measurements to change.
Forgetting the PIN when PIN authentication has been enabled.
Updating option ROM firmware.
Upgrading TPM firmware.
Adding or removing hardware. For example, inserting a new card in the computer, including some PCMIA wireless cards.
Removing, inserting, or completely depleting the charge on a smart battery on a portable computer.
Changes to the master boot record on the disk.
Changes to the boot manager on the disk.
Hiding the TPM from the operating system. Some BIOS settings can be used to prevent the enumeration of the TPM to the operating system. When implemented, this option can make the TPM hidden from the operating system. When the TPM is hidden, BIOS secure startup is disabled, and the TPM does not respond to commands from any software.
Using a different keyboard that does not correctly enter the PIN or whose keyboard map does not match the keyboard map assumed by the pre-boot environment. This can prevent the entry of enhanced PINs.
Modifying the Platform Configuration Registers (PCRs) used by the TPM validation profile. For example, including PCR[1] would result in most changes to BIOS settings, causing BitLocker to enter recovery mode.

Note

Some computers have BIOS settings that skip measurements to certain PCRs, such as PCR[2]. Changing this setting in the BIOS would cause BitLocker to enter recovery mode because the PCR measurement will be different.

Moving the BitLocker-protected drive into a new computer.
Upgrading the motherboard to a new one with a new TPM.
Losing the USB flash drive containing the startup key when startup key authentication has been enabled.
Failing the TPM self test.
Having a BIOS or an option ROM component that is not compliant with the relevant Trusted Computing Group standards for a client computer. For example, a non-compliant implementation may record volatile data (such as time) in the TPM measurements, causing different measurements on each startup and causing BitLocker to start in recovery mode.
Changing the usage authorization for the storage root key of the TPM to a non-zero value.

Note

The BitLocker TPM initialization process sets the usage authorization value to zero, so another user or process must explicitly have changed this value.

Disabling the code integrity check or enabling test signing on Windows Boot Manager (Bootmgr).
Pressing the F8 or F10 key during the boot process.
Adding or removing add-in cards (such as video or network cards), or upgrading firmware on add-in cards.
Using a BIOS hot key during the boot process to change the boot order to something other than the hard drive.

Can I swap hard disks on the same computer if BitLocker is enabled on the operating system drive?

Yes, you can swap multiple hard disks on the same computer if BitLocker is enabled, but only if the hard disks were BitLocker-protected on the same computer. The BitLocker keys are unique to the TPM and operating system drive, so if you want to prepare a backup operating system or data drive for use in case of disk failure, you need to make sure that they were matched with the correct TPM. You can also configure different hard drives for different operating systems and then enable BitLocker on each one with different authentication methods (such as one with TPM-only and one with TPM+PIN) without any conflicts.

Can I access my BitLocker-protected drive if I insert the hard disk into a different computer?

Yes, if the drive is a data drive, you can unlock it from the BitLocker Drive Encryption Control Panel item just as you would any other data drive by using a password or smart card. If the data drive was configured for automatic unlock only, you will have to unlock it by using the recovery key. If it is an operating system drive mounted on another computer running Windows 7, the encrypted hard disk can be unlocked by a data recovery agent if one was configured or it can be unlocked by using the recovery key.

Note

Mounting the hard disk on another computer running Windows 7 is a quick and straightforward way to recover information from a damaged computer that has a BitLocker-protected drive on the hard disk.

Can I dual boot Windows 7 and Windows Vista with BitLocker-protected operating system drives?

Yes. Use the following procedure to set up a dual-boot computer with BitLocker protection.

Warning

Configuring a computer for dual boot is not recommended if the computer is running Unified Extensible Firmware Interface (UEFI) firmware.

To set up a dual boot computer with BitLocker protection

Install Windows Vista with the desired partition layout (such as a partition for Windows Vista, a partition for Windows 7, and a data partition). We recommend that you create a 1.5-GB partition that can be used by the BitLocker Drive Preparation Tool as the system partition or set a 1.5-GB partition as active following the steps listed in Scenario 1 of the Windows BitLocker Drive Encryption Step-by-Step Guide for Windows Vista.
Click Start, click Control Panel, click Security, and then click BitLocker Drive Encryption.
For the drive Windows Vista is installed on, click Turn On BitLocker, and follow the BitLocker setup process. You may need to run the BitLocker Drive Preparation Tool prior to beginning BitLocker setup.
After encryption has started, follow the same steps to begin the process of encrypting any data drives that you want to access in both Windows 7 and Windows Vista.
After all of the drives you want to encrypt are fully encrypted, click Start, click Control Panel, click Security, click BitLocker Drive Encryption, and then click Turn Off BitLocker on the drive Windows Vista is installed on.
On the dialog box that appears, click Disable BitLocker.
Install Windows 7 on a separate partition.
After the installation is complete, click Start, click Control Panel, click System and Security, and then click BitLocker Drive Encryption.
For the drive Windows 7 is installed on, click Turn On BitLocker, and follow the BitLocker setup process.
After encryption is complete, click Start, click Control Panel, click System and Security, and then click BitLocker Drive Encryption.
Click Manage BitLocker for the drive Windows Vista is installed on, and then click Automatically unlock on this computer. Repeat this step for any additional data drives.
Restart the computer. From the boot options menu, choose Windows Vista.
Click Start, click Control Panel, click Security, and click BitLocker Drive Encryption.
For the drive Windows Vista is installed on, click Turn On BitLocker.

Completing this procedure will permit access to BitLocker-protected drives as follows:

When running Windows 7, you will have access to any BitLocker-protected fixed data drives and the drive Windows Vista is installed on.
When running Windows Vista, you will have access to any BitLocker-protected fixed data drives but will not be able to access the drive Windows 7 is installed on.

Why is "Turn BitLocker on" not available when I right-click a drive?

Some drives cannot be encrypted with BitLocker. Reasons a drive cannot be encrypted include insufficient disk size, an incompatible file system, or a drive is designated as the system partition. By default, the system drive (or system partition) of a computer running Windows 7 is hidden from display in the Computer window. However, if it is not created as a hidden drive when the operating system was installed due to a custom installation process, that drive might be displayed but cannot be encrypted.

What type of disk configurations are supported by BitLocker?

In Windows Server 2008 R2, Windows Server 2008, and Windows 7, any number of internal, fixed data drives can be protected with BitLocker. ATA and SATA-based, direct-attached storage devices are also supported. The following table details which disk configurations are supported and not supported by BitLocker.

Drive configuration	Supported	Not supported
Network	None	Network file system (NFS) Distributed File System (DFS)
Optical media	None	CD file system (CDFS) Live File System Universal Disk Format (UDF)
Software	Basic volumes	Software-based RAID systems Bootable and non-bootable virtual hard disks (VHDs) Dynamic volumes RAM disks
File system	NTFS FAT16 FAT32 ExFAT	CD File system
Drive connection	USB Firewire SATA SAS ATA IDE SCSI	iSCSI Fiber Channel eSATA Bluetooth
Device type	Solid state drives, such as USB flash drives Hardware-based RAID systems Hard disk drive	None

What if my disk configuration is not listed?

If your disk configuration is not listed in the previous question, it is a configuration that has not been fully tested by Microsoft.

Key management

What is the difference between a TPM owner password, recovery password, recovery key, PIN, enhanced PIN, and startup key?

There are multiple keys that can be generated and used by BitLocker. Some keys are required and some are optional protectors you can choose to use depending on the level of security you require.

TPM owner password

Prior to enabling BitLocker on a computer with a TPM version 1.2, you must initialize the TPM. The initialization process generates a TPM owner password, which is a password set on the TPM. You must be able to supply the TPM owner password to change the state of the TPM, such as when enabling or disabling the TPM or resetting the TPM lockout.

Recovery password and recovery key

When you set up BitLocker, you must choose how access to BitLocker-protected drives can be recovered in the event that the specified unlock method cannot be used (such as if the TPM cannot validate the boot components, the personal identification number (PIN) is forgotten, or the password is forgotten). In these situations, you must be able to supply either the recovery key or the recovery password to unlock the encrypted data on the drive. In Windows 7, the term "recovery key" is used generically to refer to both the recovery key file and the recovery password. When you supply the recovery information, you can use either of the following formats:

A recovery password consisting of 48 digits divided into eight groups. During recovery, you need to type this password into the BitLocker recovery console by using the function keys on your keyboard.
A key file on a USB flash drive that is read directly by the BitLocker recovery console. During recovery, you need to insert this USB device.

PIN and enhanced PIN

For a higher level of security with the TPM, you can configure BitLocker with a personal identification number (PIN). The PIN is a user-created value that must be entered each time the computer starts or resumes from hibernation. The PIN can consist of 4 to 20 digits as specified by the Configure minimum PIN length for startup Group Policy setting and is stored internally as a 256-bit hash of the entered Unicode characters. This value is never displayed to the user. The PIN is used to provide another factor of authentication in conjunction with TPM authentication.

For an even higher level of security with the TPM, you can configure BitLocker to use enhanced PINs. Enhanced PINs are PINs that use the full keyboard character set in addition to the numeric set to allow for more possible PIN combinations and are between 4 and 20 characters in length. To use enhanced PINs, you must enable the Allow enhanced PINs for startup Group Policy setting before adding the PIN to the drive. By enabling this policy, all PINs created can utilize full keyboard characters.

Note

To use enhanced PINs, your computer's BIOS must support using the full keyboard in the pre-boot environment. Users can run the optional system check during the BitLocker setup process to ensure the PIN can be entered correctly in the pre-boot environment. You should verify that the computers in your organization are compatible before making the use of enhanced PINs an organizational requirement.

When setting a BitLocker PIN by using the BitLocker setup wizard, the Manage-bde command-line tool, or through Windows Management Instrumentation (WMI) remote administration, you can use the wide character set. However, system firmware, either BIOS or Unified Extensible Firmware Interface (UEFI), may only support a standard EN-US keyboard and keymap during system startup. Additionally, BIOS-based systems are limited to 7-bit ASCII input during PIN entry. Thus, the use of either non-English characters or keys that differ in position from the EN-US keymap, such as QWERTZ and AZERTY keyboards, may cause boot-time PIN entry to fail. If your computer is affected by this limitation, it should be identified during the system check run by the BitLocker setup wizard. If it is not identified during the system check and the PIN is not able to be entered, you will need to supply the recovery key to unlock the drive.

We recommend that users set their keyboard layout to EN-US during enhanced PIN entry to avoid PIN entry failure in the pre-boot environment. If you are unable to enter an enhanced PIN from your keyboard even after setting the keyboard layout to EN-US, you must use a numeric-only PIN.

The following list identifies characters that are not currently supported by system firmware:

Roman characters on keyboards with a non-EN-US keymap. For example, "Z" and "Y" on German keyboards and "Q" and "A" on French keyboards.
Characters that are not available in 7-bit ASCII. For example, characters with umlauts, grave accents, and tildes.
Symbols that are not available in 7-bit ASCII. For example, squared superscript, fractions, copyright, trademark, and international currency symbols.

Startup key

Configuring a startup key is another method to enable a higher level of security with the TPM. The startup key is a key stored on a USB flash drive, and the USB flash drive must be inserted every time the computer starts. The startup key is used to provide another factor of authentication in conjunction with TPM authentication. To use a USB flash drive as a startup key, the USB flash drive must be formatted by using the NTFS, FAT, or FAT32 file system.

Important

You must have a startup key to use BitLocker on a non-TPM computer.

How can the recovery password and recovery key be stored?

The recovery password and recovery key for an operating system drive or a fixed data drive can be saved to a folder, saved to one or more USB devices, or printed.

For removable data drives, the recovery password and recovery key can be saved to a folder or printed. By default, you cannot store a recovery key for a removable drive on a removable drive.

A domain administrator can additionally configure Group Policy to automatically generate recovery passwords and store them in Active Directory Domain Services (AD DS) for any BitLocker-protected drive. For more information about how to store recovery information in AD DS, see Backing Up BitLocker and TPM Recovery Information to AD DS.

Is it possible to add an additional method of authentication without decrypting the drive if I only have the TPM authentication method enabled?

You can use the Manage-bde.exe command-line tool to replace your TPM-only authentication mode with a multifactor authentication mode. For example, if BitLocker is enabled with TPM authentication only and you want to add PIN authentication, use the following commands from an elevated command prompt, replacing <4-20 digit numeric PIN> with the numeric PIN you want to use:

manage-bde –protectors –delete %systemdrive% -type tpm

manage-bde –protectors –add %systemdrive% -tpmandpin <4-20 digit numeric PIN>

For more information about using Manage-bde, see the Manage-bde.exe Parameter Reference.

If I lose my recovery information, will the BitLocker-protected data be unrecoverable?

BitLocker is designed to make the encrypted drive unrecoverable without the required authentication. When in recovery mode, the user needs the recovery password or recovery key to unlock the encrypted drive. Therefore, we highly recommend that you store the recovery information in AD DS or in another safe location.

Can the USB flash drive that is used as the startup key also be used to store the recovery key?

While this is technically possible, it is not a best practice to use one USB flash drive to store both keys. If the USB flash drive that contains your startup key is lost or stolen, you also lose access to your recovery key. In addition, inserting this key would cause your computer to automatically boot from the recovery key even if TPM-measured files have changed, which circumvents the TPM's system integrity check.

Can I save the startup key on multiple USB flash drives?

Yes, you can save a computer's startup key on multiple USB flash drives. Right-clicking a BitLocker-protected drive and selecting Manage BitLocker will provide you the options to duplicate the recovery keys as needed.

Can I save multiple (different) startup keys on the same USB flash drive?

Yes, you can save BitLocker startup keys for different computers on the same USB flash drive.

Can I generate multiple (different) startup keys for the same computer?

You can generate different startup keys for the same computer through scripting. However, for computers that have a TPM, creating different startup keys prevents BitLocker from using the TPM's system integrity check.

Can I generate multiple PIN combinations?

In Windows 7, it is not possible to generate multiple PIN combinations.

What encryption keys are used in BitLocker? How do they work together?

Raw data is encrypted with the full volume encryption key, which is then encrypted with the volume master key. The volume master key is in turn encrypted by one of several possible methods depending on your authentication (that is, key protectors or TPM) and recovery scenarios. For a complete description of how encryption keys work in BitLocker, see the BitLocker Drive Encryption Technical Overview.

Where are the encryption keys stored?

The full volume encryption key is encrypted by the volume master key and stored in the encrypted drive. The volume master key is encrypted by the appropriate key protector and stored in the encrypted drive. If BitLocker has been suspended, the clear key that is used to encrypt the volume master key is also stored in the encrypted drive, along with the encrypted volume master key.

This storage process ensures that the volume master key is never stored unencrypted and is protected unless you disable BitLocker. The keys are also saved to two additional locations on the drive for redundancy. The keys can be read and processed by the boot manager.

For a complete description of how encryption keys work in BitLocker, see the BitLocker Drive Encryption Technical Overview.

Why do I have to use the function keys to enter the PIN or the 48-character recovery password?

The F1 through F10 keys are universally mapped scan codes available in the pre-boot environment on all computers and in all languages. The numeric keys 0 through 9 are not usable in the pre-boot environment on all keyboards.

When using an enhanced PIN, users should run the optional system check during the BitLocker setup process to ensure that the PIN can be entered correctly in the pre-boot environment. For more information about enhanced PINs see What is the difference between a TPM owner password, recovery password, recovery key, PIN, enhanced PIN, and startup key?

How does BitLocker help prevent an attacker from discovering the PIN that unlocks my operating system drive?

It is possible that a personal identification number (PIN) can be discovered by an attacker performing a brute force attack. A brute force attack occurs when an attacker uses an automated tool to try different PIN combinations until the correct one is discovered. For BitLocker-protected computers, this type of attack, also known as a dictionary attack, requires that the attacker have physical access to the computer.

The TPM has the built-in ability to detect and react to these types of attacks. Because different manufacturers' TPMs may support different PIN and attack mitigations, contact your TPM's manufacturer to determine how your computer's TPM mitigates PIN brute force attacks.

After you have determined your TPM's manufacturer (see How can I determine the manufacturer of my TPM?), contact the manufacturer to gather the TPM's vendor-specific information. Most manufacturers use the PIN authentication failure count to exponentially increase lockout time to the PIN interface. However, each manufacturer has different policies regarding when and how the failure counter is decreased or reset.

How can I evaluate a TPM's dictionary attack mitigation mechanism?

The following questions can assist you when asking a TPM manufacturer about the design of a dictionary attack mitigation mechanism:

How many failed authorization attempts can occur before lockout?
What is the algorithm for determining the duration of a lockout based on the number of failed attempts and any other relevant parameters?
What actions can cause the failure count and lockout duration to be decreased or reset?

Can PIN length and complexity be managed with Group Policy?

Yes. In Windows 7, you can configure the minimum personal identification number (PIN) length by using the Configure minimum PIN length for startup Group Policy setting and allow the use of alphanumeric PINs by enabling the Allow enhanced PINs for startup Group Policy setting. However, you cannot require PIN complexity by Group Policy.

How are the PIN and TPM used to derive the volume master key?

BitLocker hashes the user-specified personal identification number (PIN) by using SHA-256, and the first 160 bits of the hash are used as authorization data sent to the TPM to seal the volume master key. The volume master key is now protected by both the TPM and the PIN. To unseal the volume master key, you are required to enter the PIN each time the computer restarts or resumes from hibernation.

BitLocker To Go

What is BitLocker To Go?

BitLocker To Go is BitLocker Drive Encryption on removable data drives. This includes the encryption of USB flash drives, SD cards, external hard disk drives, and other drives formatted by using the NTFS, FAT16, FAT32, or exFAT file systems.

How can I authenticate or unlock my removable data drive?

In Windows 7, you can unlock removable data drives by using a password or a smart card. After you've started encryption, the drive can also be automatically unlocked on a specific computer for a specific user account. System administrators can configure which options are available for users, as well as password complexity and minimum length requirements.

Can I use BitLocker To Go with computers running Windows XP or Windows Vista?

Yes. By default if the removable data drive is formatted by using the FAT file system and then locked with BitLocker To Go using a computer running Windows 7, it can be unlocked on a computer running Windows XP or Windows Vista. However, the files will available with read-only access on those operating systems and no files will be able to be added to the removable drive from those computers. When you insert the removable drive into a computer running Windows XP or Windows Vista, the only readable file on the drive is the BitLocker To Go Reader application, which is automatically written to the drive when BitLocker protection is turned on for the drive in Windows 7. By running the BitLocker To Go Reader, you will be able to view the files on the BitLocker-protected removable drive.

Note

The BitLocker To Go Reader is not supported on removable drives formatted with NTFS.

What happens if I try to open a BitLocker-protected, NTFS-formatted removable drive by using a computer running Windows XP or Windows Vista?

In most cases, Windows XP and Windows Vista will not be able to recognize a BitLocker-protected, NTFS-formatted removable drive. In many situations, the user will be prompted to format the drive. Because of this, it is recommended that removable drives be formatted by using the FAT, FAT32, or exFAT file system when using BitLocker.

Is there a way to ensure the BitLocker To Go Reader is not installed on FAT-formatted drives?

Yes. Group Policy can prevent the application from being installed on the drives. The first option is to disable the policy settings that allow computers running Windows Vista, Windows XP with Service Pack 3 (SP3), or Windows XP with Service Pack 2 (SP2) to open BitLocker-protected data drives. These policy settings are located in the Local Group Policy Editor in Windows 7 or the Group Policy Management Console in Windows Server 2008 R2 in the following locations:

Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Removable Data Drives\Allow access to BitLocker-protected removable data drives from earlier versions of Windows
Computer Configuration\Administrative Templates\Windows Components\BitLocker Drive Encryption\Fixed Data Drives\Allow access to BitLocker-protected fixed data drives from earlier versions of Windows

To allow computers running Windows Vista, Windows XP with SP3, or Windows XP with SP2 to open BitLocker-protected data drives but prevent the BitLocker To Go Reader application from being installed on the drive, enable these policy settings and select the Do not install BitLocker To Go Reader on FAT formatted removable drives and Do not install BitLocker To Go Reader on FAT formatted fixed drives check boxes on the respective policy settings.

Note

Before deleting the BitLocker To Go Reader from a drive, BitLocker checks that the identification field of the drive is either blank or matches the identification field for your organization.

Can I save files to my BitLocker-protected removable drive when I am using Windows XP or Windows Vista?

No. The BitLocker To Go Reader provides read-only access to BitLocker-protected removable drives.

Can I download a copy of the BitLocker To Go Reader?

Yes. To download the BitLocker To Go Reader, see https://go.microsoft.com/fwlink/?LinkID=151425.

Why am I unable to access my removable drive on computers running Windows XP or Windows Vista when using the BitLocker To Go Reader?

The most common reason for this situation is that the drive is not formatted by using the FAT, FAT32, or exFAT file systems. To check for this, insert the drive in a computer running Windows 7, right-click the drive, and then click Properties to see the file format of the drive. Another reason could be that the system administrator has disabled access to removable drives from previous versions of Windows by using the BitLocker Group Policy settings. To check for this, attempt to access the drive from a computer running Windows XP or Windows Vista that is not joined to the domain.

Important

You should ensure that BitLocker has finished the encryption process on your drive before attempting to view the drive by using the BitLocker To Go Reader.

Active Directory Domain Services (AD DS)

Important

For detailed instructions about how to configure AD DS for BitLocker, see Backing Up BitLocker and TPM Recovery Information to AD DS.

Does BitLocker require a schema extension to store recovery information in AD DS?

This depends on the operating system and AD DS implementation.

Windows Server 2003 with Service Pack 1 (SP1)

In Windows Server 2003 with SP1, the schema must be extended to support storing BitLocker and TPM recovery and password information.

Windows Server 2008 and Windows Server 2008 R2

In Windows Server 2008 and Windows Server 2008 R2, the schema already includes the required attributes.

What type of information is stored in AD DS?

Three primary pieces of information are stored in AD DS. The following table details this information.

Stored information	Description
Hash of the TPM owner password	The password hash can be stored only if the TPM is owned and the ownership was taken by using components of Windows 7, such as the BitLocker Setup Wizard or the TPM snap-in.
BitLocker recovery password	The recovery password allows you to unlock and access the drive in the event of a recovery incident. Domain administrators can view the BitLocker recovery password by using the BitLocker Recovery Password Viewer. For more information about this tool, see BitLocker Recovery Password Viewer for Active Directory.
BitLocker key package	The key package helps to repair damage to the hard disk that would otherwise prevent standard recovery. Using the key package for recovery requires the BitLocker Repair Tool, Repair-bde. For more information about this command-line tool, see Repair-bde.exe Parameter Reference (https://go.microsoft.com/fwlink/?LinkId=162622).

Does BitLocker encrypt recovery information as it is sent to AD DS?

Yes, the transmission of recovery information from a Windows 7–based client computer to AD DS is protected by using the Kerberos authentication protocol. Specifically, the connection uses the authentication flags ADS_SECURE_AUTHENTICATION, ADS_USE_SEALING, and ADS_USE_SIGNING.

For more information about Active Directory authentication flags, see ADS_AUTHENTICATION_ENUM Enumeration (https://go.microsoft.com/fwlink/?LinkId=79643).

Note

After recovery information is transmitted, AD DS does not store the BitLocker and TPM recovery information in an encrypted format. However, access control permissions are set so that only domain administrators or appropriate delegates can read the stored information when the server is online. Enterprises concerned about offline attacks on branch office servers should consider enabling BitLocker on those servers. We also recommended configuring your domain controllers to support encryption sealing and that any recovery retrieval application used in your organization use sealing as well.
For more information about developing applications that exchange encrypted data over a network, see the following articles on MSDN:

Binding with Encryption (https://go.microsoft.com/fwlink/?LinkId=151844)
Using ldap_init (https://go.microsoft.com/fwlink/?LinkId=151845)

For more information about configuring servers to support encryption sealing, see the following articles:

Using SASL (https://go.microsoft.com/fwlink/?LinkId=151846)
Using SSL/TLS (https://go.microsoft.com/fwlink/?LinkId=151847)
How to enable LDAP signing in Windows Server 2008 (https://go.microsoft.com/fwlink/?LinkId=151848)

Is the BitLocker recovery information stored in plaintext in AD DS?

Yes, the recovery information is stored unencrypted in AD DS, but the entries have access control lists (ACLs) that limit access to only domain administrators.

If an attacker gains full access to AD DS, all computers in the domain, including BitLocker-protected computers, can be compromised. For more information about securing access to AD DS, see Securing Active Directory Administrative Groups and Accounts (https://go.microsoft.com/fwlink/?LinkId=83266).

What if BitLocker is enabled on a computer before the computer has joined the domain?

If BitLocker is enabled on a drive before Group Policy has been applied to enforce backup, the recovery information will not be automatically backed up to AD DS when the computer joins the domain or when Group Policy is subsequently applied. However, in Windows 7 you can use the Choose how BitLocker-protected operating system drives can be recovered, Choose how BitLocker-protected fixed drives can be recovered and Choose how BitLocker-protected removable drives can be recovered Group Policy settings to require that the computer be connected to a domain before BitLocker can be enabled to help ensure that recovery information for BitLocker-protected drives in your organization is backed up to AD DS.

The BitLocker Windows Management Instrumentation (WMI) interface does allow administrators to write a script to back up or synchronize an online client's existing recovery information; however, BitLocker does not automatically manage this process. The Manage-bde command-line tool can also be used to manually back up recovery information to AD DS. For example, to back up all of the recovery information for the C: drive to AD DS, you would use the following command from an elevated command prompt: manage-bde –protectors -adbackup C:.

Important

Joining a computer to the domain should be the first step for new computers within an organization. After computers are joined to a domain, storing the BitLocker recovery key to AD DS is automatic (when enabled in Group Policy).

Is there an event log entry recorded on the client computer to indicate the success or failure of the Active Directory backup?

Yes, an event log entry that indicates the success or failure of an Active Directory backup is recorded on the client computer. However, even if an event log entry says "Success," the information could have been subsequently removed from AD DS, or BitLocker could have been reconfigured in such a way that the Active Directory information can no longer unlock the drive (such as by removing the recovery password key protector). In addition, it is also possible that the log entry could be spoofed.

Ultimately, determining whether a legitimate backup exists in AD DS requires querying AD DS with domain administrator credentials by using the BitLocker password viewer tool.

If I change the BitLocker recovery password on my computer and store the new password in AD DS, will AD DS overwrite the old password?

No. By design, BitLocker recovery password entries do not get deleted from AD DS; therefore, you might see multiple passwords for each drive. To identify the latest password, check the date on the object.

What happens if the backup initially fails? Will BitLocker retry the backup?

If the backup initially fails, such as when a domain controller is unreachable at the time when the BitLocker setup wizard is run, BitLocker does not try again to back up the recovery information to AD DS.

When an administrator selects the Require BitLocker backup to AD DS check box of the Store BitLocker recovery information in Active Directory Domain Service (Windows 2008 and Windows Vista) policy setting, or the equivalent Do not enable BitLocker until recovery information is stored in AD DS for (operating system | fixed data | removable data) drives check box in any of the Choose how BitLocker-protected operating system drives can be recovered, Choose how BitLocker-protected fixed data drives can be recovered, Choose how BitLocker-protected removable data drives can be recovered policy settings, this prevents users from enabling BitLocker unless the computer is connected to the domain and the backup of BitLocker recovery information to AD DS succeeds. With these settings configured if the backup fails, BitLocker cannot be enabled, ensuring that administrators will be able to recover BitLocker-protected drives in the organization.

When an administrator clears these check boxes, the administrator is allowing a drive to be BitLocker-protected without having the recovery information successfully backed up to AD DS; however, BitLocker will not automatically retry the backup if it fails. Instead, administrators can create a script for the backup, as described earlier in What if BitLocker is enabled on a computer before the computer has joined the domain? to capture the information after connectivity is restored.

Security

What form of encryption does BitLocker use? Is it configurable?

BitLocker uses Advanced Encryption Standard (AES) as its encryption algorithm with configurable key lengths of 128 or 256 bits, as well as an optional Diffuser. The default encryption setting is AES-128 with Diffuser, but the options are configurable by using Group Policy. For additional information about the BitLocker encryption method, see AES-CBC + Elephant diffuser in the Microsoft Download Center (https://go.microsoft.com/fwlink/?LinkId=80598).

What is the Diffuser?

The Diffuser is an algorithm that is designed to mitigate a possible class of attacks that involve changing encrypted information to introduce a security vulnerability into the system. With the Diffuser, small changes to the encrypted cipher text of a sector affect the entire sector when the data is decrypted. This behavior makes targeted attacks much more difficult to perform. For additional information about the BitLocker encryption method, see AES-CBC + Elephant diffuser in the Microsoft Download Center (https://go.microsoft.com/fwlink/?LinkId=80598).

What is best practice for using BitLocker on an operating system drive?

The recommended practice for BitLocker configuration on an operating system drive is to implement BitLocker on a computer with a TPM version 1.2 and a Trusted Computing Group (TCG)-compliant BIOS implementation, plus a PIN. By requiring a PIN that was set by the user in addition to the TPM validation, a malicious user that has physical access to the computer cannot simply start the computer.

What are the implications of using the sleep or hibernate power management options?

BitLocker on operating system drives in its basic configuration (with a TPM but without advanced authentication) provides additional security for the hibernate mode. However, BitLocker provides greater security when it is configured to use an advanced authentication mode (TPM+PIN, TPM+USB, or TPM+PIN+USB) with the hibernate mode. This method is more secure because returning from hibernation requires BitLocker authentication. As a best practice, we recommend that sleep mode be disabled and that you use TPM+PIN for the authentication method.

What are the advantages of a TPM?

Most operating systems use a shared memory space and rely on the operating system to manage physical memory. A TPM is a hardware component that uses its own internal firmware and logic circuits for processing instructions, thus shielding it from external software vulnerabilities. Attacking the TPM requires physical access to the computer. Additionally, the tools and skills necessary to attack hardware are often more expensive, and usually are not as available as the ones used to attack software. And because each TPM is unique to the computer that contains it, attacking multiple TPM computers would be difficult and time-consuming.

Note

Configuring BitLocker with an additional factor of authentication provides even more protection against TPM hardware attacks.

Is Microsoft pursuing any security certification for BitLocker?

All of the versions of BitLocker that have been included with the operating system have obtained the Federal Information Processing Standard (FIPS) 140-2 certification, and have been Common Criteria certified EAL4+.

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BitLocker Drive Encryption in Windows 7: Frequently Asked Questions

Overview and requirements

Upgrading

Deployment and administration

Key management

BitLocker To Go

Active Directory Domain Services (AD DS)

Security

Other questions

Overview and requirements

What is BitLocker? How does it work?

Does BitLocker support multifactor authentication?

What are the BitLocker hardware and software requirements?

BitLocker hardware and software requirements for operating system drives

BitLocker hardware and software requirements for data drives

Why are two partitions required? Why does the system drive have to be so large?

Which Trusted Platform Modules (TPMs) does BitLocker support?

How can I tell whether my computer has a TPM version 1.2?

Can I use BitLocker on an operating system drive without a TPM version 1.2?

How do I obtain BIOS support for the TPM on my computer?

What credentials are required to use BitLocker?

Upgrading

What versions of Windows 7 include BitLocker? Can I use BitLocker on a Windows XP–based computer?

Can I upgrade my Windows XP–based computer to Windows 7 with the necessary disk configuration for BitLocker?

Can I upgrade my Windows Vista–based computer to Windows 7 with BitLocker enabled?

What is the difference between disabling, suspending, and decrypting when I turn off BitLocker?

Do I have to decrypt my BitLocker-protected drive to download and install system updates and upgrades?

Deployment and administration

Can BitLocker deployment be automated in an enterprise environment?

Can BitLocker encrypt more than just the operating system drive?

Is there a noticeable performance impact when BitLocker is enabled on a Windows 7–based computer?

Approximately how long will initial encryption take when BitLocker is turned on?

What happens if the computer is turned off during encryption or decryption?

Why does it appear that most of the free space in my drive is used when BitLocker is converting the drive?

Does BitLocker encrypt and decrypt the entire drive all at once when reading and writing data?

How can I prevent users on a network from storing data on an unencrypted drive?

What system changes would cause the integrity check on my operating system drive to fail?

What causes BitLocker to start into recovery mode when attempting to start the operating system drive?

Can I swap hard disks on the same computer if BitLocker is enabled on the operating system drive?

Can I access my BitLocker-protected drive if I insert the hard disk into a different computer?

Can I dual boot Windows 7 and Windows Vista with BitLocker-protected operating system drives?

To set up a dual boot computer with BitLocker protection

Why is "Turn BitLocker on" not available when I right-click a drive?

What type of disk configurations are supported by BitLocker?

What if my disk configuration is not listed?

Key management

What is the difference between a TPM owner password, recovery password, recovery key, PIN, enhanced PIN, and startup key?

How can the recovery password and recovery key be stored?

Is it possible to add an additional method of authentication without decrypting the drive if I only have the TPM authentication method enabled?

If I lose my recovery information, will the BitLocker-protected data be unrecoverable?

Can the USB flash drive that is used as the startup key also be used to store the recovery key?

Can I save the startup key on multiple USB flash drives?

Can I save multiple (different) startup keys on the same USB flash drive?

Can I generate multiple (different) startup keys for the same computer?

Can I generate multiple PIN combinations?

What encryption keys are used in BitLocker? How do they work together?

Where are the encryption keys stored?

Why do I have to use the function keys to enter the PIN or the 48-character recovery password?

How does BitLocker help prevent an attacker from discovering the PIN that unlocks my operating system drive?

How can I evaluate a TPM's dictionary attack mitigation mechanism?

Can PIN length and complexity be managed with Group Policy?

How are the PIN and TPM used to derive the volume master key?

BitLocker To Go

What is BitLocker To Go?

How can I authenticate or unlock my removable data drive?

Can I use BitLocker To Go with computers running Windows XP or Windows Vista?

What happens if I try to open a BitLocker-protected, NTFS-formatted removable drive by using a computer running Windows XP or Windows Vista?

Is there a way to ensure the BitLocker To Go Reader is not installed on FAT-formatted drives?

Can I save files to my BitLocker-protected removable drive when I am using Windows XP or Windows Vista?

Can I download a copy of the BitLocker To Go Reader?

Why am I unable to access my removable drive on computers running Windows XP or Windows Vista when using the BitLocker To Go Reader?

Active Directory Domain Services (AD DS)

Does BitLocker require a schema extension to store recovery information in AD DS?

What type of information is stored in AD DS?

Does BitLocker encrypt recovery information as it is sent to AD DS?

Is the BitLocker recovery information stored in plaintext in AD DS?

What if BitLocker is enabled on a computer before the computer has joined the domain?

Is there an event log entry recorded on the client computer to indicate the success or failure of the Active Directory backup?

If I change the BitLocker recovery password on my computer and store the new password in AD DS, will AD DS overwrite the old password?