Another great question from last week’s Windows 7 class. The question was posed – “If I upgrade something like RAM in the system, will it trigger the boot integrity check to fail and enter a lockout state?”

The following conditions or actions can trigger such an event.. Taken from TechNet’s Bitlocker on Win 7 FAQ

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 settings with the exception of the following items:
    BCDE_LIBRARY_TYPE_DESCRIPTION, FVE_BCD_UNPROTECTED_DATATYPE
    BCDE_DEVICE_TYPE_RAMDISK_IMAGE_OFFSET, FVE_BCD_UNPROTECTED_DATATYPE
    BCDE_MEMTEST_TYPE_PASS_COUNT, FVE_BCD_UNPROTECTED_DATATYPE
    BCDE_MEMTEST_TYPE_TESTMIX, FVE_BCD_UNPROTECTED_DATATYPE
    BCDE_MEMTEST_TYPE_FAILURE_COUNT, FVE_BCD_UNPROTECTED_DATATYPE
    BCDE_MEMTEST_TYPE_TEST_TO_FAIL, FVE_BCD_UNPROTECTED_DATATYPE
  • 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. If a portable computer is connected to its docking station when BitLocker is turned on, then it must be connected to the docking station when it is unlocked. If a portable computer is not connected to its docking station when BitLocker is turned on, then it must not be connected to 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.

    noteNote

    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.

    noteNote

    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.
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