Windows

Encryption Algorithm: Why does MBAM not automatically re-encrypt MBAM or Bitlocker protected devices

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Once a drive is encrypted by BitLocker, it can only be unlocked or decrypted with a Bitlocker password or the Bitlocker Recovery Key. And anyone without proper authentication will be denied access even if the computer has been stolen or the hard disk is taken. It uses Advanced Encryption Standard (AES) encryption algorithm with 128-bit or 256-bit keys for encrypting data in the entire drive or only used space of the drive. Kindly refer to these related guides: How to unlock a fixed drive protected by BitLocker, how to deploy Microsoft BitLocker Administration and Monitoring Tool, how to correctly disable Microsoft BitLocker Administration and Monitoring encrypted devices, how to uninstall your current version of MBAM and run setup again, and Microsoft Desktop Optimization Pack [MDOP] at a glance (AGPM, MBAM, App-V, DaRT, MED-V, and UE-V).

We employ Group Policy Object to enforce BitLocker drive encryption on client computers in an enterprise environment. 

When would you encounter this issue?

  • By default, if you do not specify a different encryption method other than AES-128-bit, BitLocker will use the default encryption method (AES 128-bit). You will find more information in this link.
  • If you disable or don’t configure these settings , BitLocker will use the default encryption method (AES 128-bit).
  • You have already enabled BitLocker to protect my personal device and now there is an organisation wide policy to protect devices with MBAM to ensure compliance by all devices.

MBAM doesn’t re-encrypt drives that are already protected with BitLocker Drive Encryption. If you deploy a BitLocker management policy that doesn’t match the drive’s current protection, it reports as non-compliant. The drive is still protected.

For example, you have used BitLocker to encrypt the drive with AES-XTS 128 encryption algorithm, but the MBAM or the Configuration Manager policy requires AES-XTS 256. The drive is non-compliant with the policy, even though the drive is encrypted. Therefore, if a different encryption algorithm is not used, MBAM will not automatically re-encrypt the device.

Resolution

To work around this issue, you will need to first disable BitLocker on the device. Then deploy a new policy with the new settings that will apply the AES-XTS 256 encryption algorithm.

MBAM or the Configuration Manager is capable of taking over BitLocker protected device if it is automatically encrypted with the same encryption key (encryption algorithm).

MBAM Drawback

The following are the things MBAM cannot do. You may want to see this guide for what MBAM cannot do such as “Effect of renaming an MBAM or BitLocker protected Computer“. The following are the things MBAM cannot do.

  • Decrypt systems and re-encrypt with the right algorithms. We have already seen this multiple times.
  • Automatically update a device that is renamed to a new name.
  • Force users to change the PIN in XX number of days.
  • Force a change to the recovery key in an xx number of days etc.”

I hope you found this blog post helpful. If you have any questions, please let me know in the comment session.

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