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Purportedly Windows makes use of this, FWIW: https://learn.microsoft.com/en-us/windows/security/operating-system-security/data-protection/bitlocker/countermeasu

by bri3d 2y ago

Purportedly Windows makes use of this, FWIW: https://learn.microsoft.com/en-us/windows/security/operating-system-security/data-protection/bitlocker/countermeasures https://learn.microsoft.com/en-us/windows/security/operating... "BitLocker uses the TCG Reset Attack Mitigation, also known as MOR bit (Memory Overwrite Request), before extracting keys into memory." I would extremely not trust most platform implementation of TCG Reset Attack Mitigation, though. I've never seen a UEFI platform that is even close to correctly implemented in any form. It would be interesting to know which platform this researcher was working with, and whether it purports to support the MOR bit or not.

bangaladore 2y ago
> "BitLocker uses the TCG Reset Attack Mitigation, also known as MOR bit (Memory Overwrite Request), before extracting keys into memory." (Edit: No this is a UEFI request to clear memory. Below is incorrect.) I don't think this is what the commenter was mentioning. I think this essentially makes it only possible to extract the key from the TPM once and then the TPM needs to be powered off and back on to get it again. The TPM has no control over whats in the system memory, so if they key is in system memory, no TPM mitigations are going to help. UEFI firmware must support clearing the keys from RAM.
- mjg59 2y ago
  This is exactly what I was mentioning. Despite being a TCG spec, it's implemented in firmware and has no hard requirement on a TPM at all.
  - bangaladore 2y ago
    Okay, thanks for the correction. The naming there is definitely confusing. Particularly as it sounds like a key attribute bit.
gruez 2y ago
>However, this measure can still be circumvented by removing the memory module from the system and reading it back on another system under the attacker's control that does not support these measures https://en.wikipedia.org/wiki/Cold_boot_attack https://en.wikipedia.org/wiki/Cold_boot_attack

by bri3d 2y ago

bangaladore 2y ago

> "BitLocker uses the TCG Reset Attack Mitigation, also known as MOR bit (Memory Overwrite Request), before extracting keys into memory." (Edit: No this is a UEFI request to clear memory. Below is incorrect.) I don't think this is what the commenter was mentioning. I think this essentially makes it only possible to extract the key from the TPM once and then the TPM needs to be powered off and back on to get it again. The TPM has no control over whats in the system memory, so if they key is in system memory, no TPM mitigations are going to help. UEFI firmware must support clearing the keys from RAM.

mjg59 2y ago
This is exactly what I was mentioning. Despite being a TCG spec, it's implemented in firmware and has no hard requirement on a TPM at all.
- bangaladore 2y ago
  Okay, thanks for the correction. The naming there is definitely confusing. Particularly as it sounds like a key attribute bit.

gruez 2y ago

>However, this measure can still be circumvented by removing the memory module from the system and reading it back on another system under the attacker's control that does not support these measures https://en.wikipedia.org/wiki/Cold_boot_attack https://en.wikipedia.org/wiki/Cold_boot_attack