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From what I've been reading, the guideline regarding manually changing the size of a Bitlocker encrypted partition is: (a) decrypt the partition. (b) resize the partition. (c) re-encrypt the partition.

Now, I'm wondering whether it's theoretically possible to resize a partition encrypted using Bitlocker (I specifically refer to Bitlocker utilizing software encryption, not hardware encryption, since this is the default and more secure option) without decrypting it first or would it render the partition unusable?

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  • If it is a function that is available in the OS, then malware with the correct permissions could do it. I'm not sure why you are looking at a case where a running malware process would need to resize an unaccessible partition. Once it is running, the partition is available to the OS...
    – schroeder
    Jan 6, 2021 at 12:57
  • Ultimately, you are asking if it is possible to resize a partition without decrypting it. That's more of a pure Windows question than a security question. Adding malware to the mix seems unnecessary.
    – schroeder
    Jan 6, 2021 at 12:58
  • @ schroeder That's a good point, I've edited the question per your suggestion.
    – Amit
    Jan 6, 2021 at 14:03
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    If the volume has been unlocked, hence you know what sectors are used/free the shrinking process should be the same as for a regular volume (independently if the drive is hardware or software encrypted). Of course if it is a system drive and Bitlocker is TPM protected next boot may fail because the TPM state does no longer matches. Therefore it would be required to stop Bitlocker temporarily or us a recovery key on next boot.
    – Robert
    Jan 6, 2021 at 15:49

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