alt Hacker NewsWindows uses TPM for Bitlocker. A very common scenario where TPMs get reset is BIOS updates (when a TPM is implemented in firmware). AFAIK, Windows cheats here because it also manages BIOS updates. When an update happens, it takes extra steps to preserve the Bitlocker encryption key in plaintext, and re-seals it to the TPM after the update completes.
Apart from Windows, there are many setups that fail in fun ways: Kubernetes pods that migrate from one VM with a TPM to another one, hypervisors that mount a virtual TPM to VMs, containers or VM images that do Tailscale registration on one machine and then get replicated to others, etc.
Tailscale already did some attempts at cleverness when deciding whether to enable features using a TPM (e.g. probing for TPM health/version on startup, disabling node state encryption on Kubernetes pods), but there was still a long tail of edge cases.
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> Windows cheats here
Slightly off-topic: it also cheats in how TPM works for Bitlocker when you do TPM + PIN. One would assume PIN becomes part of the encryption key, but in reality, it's just used as the auth for TPM to release the key. So while it sounds like a two-factor solution, in reality it's just single factor.
So the Bitlocker without TPM is actually a better idea and Windows makes it very painful to do if TPM is on.
> Windows cheats here because it also manages BIOS updates
Is this (relatively) new?
I don't use TPM and I rarely update BIOS unless I really need to, but I thought there was an option on my BIOS/UEFI to use USB drive to update it. How would Windows know about it?
On Windows, certificates can also be stored in the TPM.
> Bitlocker encryption key in plaintext
Actually, this is not the case. BitLocker wraps the key, meaning even if the TPM were compromised, one would still have to brute-force the PIN for the actual key. It’s cryptsetup on Linux that stores the key on the TPM in plaintext. This vulnerability has been known for quite a while and nothing has been done about it so far.
https://arxiv.org/abs/2304.14717
https://github.com/systemd/systemd/issues/37386
https://github.com/systemd/systemd/pull/27502