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Comment by Thaxll | Hacker News Reader

TPM is really badly implemented. When you upgrade your firmware, OS, everything can go south.

Just upgrading your firmware with bitlocker enabled can brick your PC.

Windows uses full disk encryption with keys from the TPM by default.

Nobody says "disable disk encryption right away incase the tom forgets the keys". The vast majority of TPM's manage to not forget the keys.

They may not say "turn off bitlocker", but people definitely recommend backing up the recovery keys, and windows allows you to back up the key to microsoft because they know people won't actually back them up. Not sure if that happens by default, but they provide a variety of options for the recovery keys because there is definitely a non-zero chance you need them. There were several stories of this happening with the windows 10->11 upgrade push, where people were auto-updated and then scrambling to decrypt their hard drives.

I'm curious. If the motherboard with the TPM dies, you're basically locked out of your data right? Keys backed up on MS server or not.

No, the backed up keys (MS server, file, printed) give you full access, they contain the full encryption key.

I suspect that they do not actually contain the encryption key. It is more convenient if the disk encryption key is stored on the disk, but separately encrypted. You actually want to store the key multiple times, one for each unlock method. If the disk can be unlocked with a password, then you store the key encrypted using the password (or encrypted using the output of a key derivation function run on the typed password). If it can be unlocked with a smartcard, then you store a copy that is encrypted using a key stored in the card. When Bitlocker uses the TPM, it no doubt asks the TPM to encrypt the key and then stores that on the disk. To decrypt the disk it can ask the TPM to decrypt the stored key, which will only succeed if the TPM is in the same state that it was in when the key was encrypted.

The reason it's done this way is to allow multiple methods of accessing the disk, to allow the encryption password to be changed without having to rewrite every single sector of the disk, etc, etc. You can even “erase” the disk in one swift operation by simply erasing all copies of the key.

That is also required for any kind of key rotation to work, you're getting new key for a key, because alternative of using key directly would mean re-encrypting the whole drive when it changes and of course only having single one instead of multiple

So if you’re using the TPM based encryption you’d better have a working backup system.

How many home users have that? How many stories of personal data loss are we going to hear as windows 11 ready PCs start to die?

don't worry, ms pushes users to just put data on onedrive, they will start losing data far before machines actually die. We already had plenty of stories of that mess.

https://boingboing.net/2026/01/05/everyone-hates-onedrive-mi...

Working backups are important regardless, but if you use a TPM then you’d better have your recovery keys somewhere convenient. I’m sure you can print them out and keep them in your wallet or something.

If windows is encrypted with keys from the TPM anyways, then tailscale doesn't need to encrypt a second time.

Windows also bit me in the ass with this feature, but tailscale not enabling encryption wouldn't have helped one iota.

Local software could be stealing plaintext secrets from your encrypted disk. Physical access is not the only attack vector.

The only way to protect against that is if a secure application boundary is enforced by the operating system. You can make it harder for other programs to uncover secrets by encrypting them, but any other application can reverse the encryption. I don't believe using the tpm meaningfully changes that situation.

> TPM is really badly implemented. When you upgrade your firmware, OS, everything can go south.

Could you elaborate ? Firmware/OS should not affect TPM contents ? Otherwise e.g. TPM-reliant Windows installs would break ?

In addition there are cloud scenarios where your VM has a TPM and you want to e.g .stop a malicious actor poaching your VM and running it elsewhere.

Having the tailscale TPM tied to your cloud hypervisor prevents the "lift and shift" attack.

Everytime I have to upgrade my MB firmware it breaks bitlocker and I have to either use restoring keys from microsoft website or disable bitlocker encryption before the upgrade.

https://www.reddit.com/r/MSI_Gaming/comments/15w8wgj/psa_tpm...

You cant reliably store secrets in tpm and expect it to work after an os update. Windows is using workarounds during windows update to avoid breaking bitlocker.

https://learn.microsoft.com/en-us/windows/security/hardware-...

You are correct. Updating the firmware or the OS does not actually erase the TPM. What is really going on is that the TPM register holds a value that is like a hash. Each time you measure the system state you update the register with a hash of the previous value and the measurement. When you ask the TPM to hold a key you specify which register value is used to encrypt the key. Later when you use the key it will fail if the TPM cannot decrypt the key. This can only happen if the TPM register has the wrong value, which can only happen if someone has tampered with the system. But voluntarily upgrading the BIOS or the OS looks exactly like tampering.

The correct procedure is to unlock the keys, copy them out of the TPM, perform the upgrade, reboot to remeasure the system state, then finally store the keys back into the TPM.

Wouldn't you want TPM to brick the machine if the firmware was modified? If something or someone modified your firmware, do you want the TPM key to remain intact? Its something you need to be aware of when upgrading firmware, disable encryption that relies on TPM or make a backup copy of the key.

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