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A comment on TPM on Embedded Systems: Pitfalls and Caveats to Watch Out For. Parent comment

Re:TPM on Embedded Systems: Pitfalls and Caveats to Watch Ou... by zauguin on Wednesday January 21, 2026 @02:17PM (#46710160)
Can't that just be done by sealing to PCRs? By protecting the unsealing key with PCR which depends on the OS (I usually use the secure boot signing key PCRs since they are different between systems and stable across updates) and some PCR which gets extended by the OS (or for stuff stored in NV making it readlocked during boot). Then any process that launches later can no longer access it and booting another OS also doesn't help.
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Re:TPM on Embedded Systems: Pitfalls and Caveats to Watch Ou... by amluto on Wednesday January 21, 2026 @02:47PM (#46710601)
That helps with FDE (except to the extent that one might want to connect an encrypted device after boot), but it doesn't help in the slightest with SSH keys. The TPM has nothing remotely resembling per-user PCRs.
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Re:TPM on Embedded Systems: Pitfalls and Caveats to Watch Ou... by Foxboron on Wednesday January 21, 2026 @03:34PM (#46711164)
> The TPM has nothing remotely resembling per-user PCRs.

The system could extend one of the PCRs, or an NVPCR, with some unique user credential locked to the user directory. Then you can't recreate the PCR records in any immediate way.

But you can't just recreate a key under one of the hierarchies anyway. You still need to posses the keyfile.

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Re:TPM on Embedded Systems: Pitfalls and Caveats to Watch Ou... by amluto on Wednesday January 21, 2026 @05:33PM (#46712582)
> The system could extend one of the PCRs, or an NVPCR, with some unique user credential locked to the user directory. Then you can't recreate the PCR records in any immediate way.

Sure, but can the system context-switch that PCR between two different users?

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Re:TPM on Embedded Systems: Pitfalls and Caveats to Watch Ou... by Foxboron on Tuesday January 27, 2026 @05:01PM (#46787601)
> Sure, but can the system context-switch that PCR between two different users?

Right, no it can't.

But this was not really something the TPM was suppose to solve.

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