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by josephg 963 days ago
TPM chips are pretty open. I had a look through the spec & API for tpm 2.0 a few years ago and there’s a lot of neat tricks you can do with them. TPM chips are an open standard with many implementations.

As far as I can tell, as a software developer you have full access to the chip. The only thing you can’t do with them (by design) is read the signing keys or generate secure boot attestations for machines which didn’t secure boot. I think you can even replace the signing keys entirely if you want to.

They aren’t a hard drive. They don’t store your data. And unfortunately I don’t think they’ll do much to prevent software bugs from causing problems. Particularly in the operating system, where software bugs can undermine the entire chain of trust model.

Don’t get me wrong; the idea of getting my computer to cryptographically prove it’s running in some locked down Xbox mode to be allowed to play Netflix or do online banking is quite the ask. The hackability of computers is one of their best features and I don’t want that genie to go back in the bottle.

But every time the conversation comes up there’s so much misinformation about them. People conflate tpm chips with intel’s management engine (which is secret and closed source), Apple’s secure enclosure (which I think can store some data?) and other stuff that works really differently.
2 comments
marklar423 963 days ago
That's pretty interesting. I wonder if replacing the signing keys could help negate DRM-y uses of the TPM
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josephg 962 days ago
Doubtful. TPM chips come pre loaded with signing keys from the manufacturer. That allows 3rd parties to verify that an attestation made by your TPM is genuine. (They can do that by checking signatures all the way back to the manufacturer’s public cert).

If you replace the manufacturer’s signing keys with some keys you generated yourself, the only real effect is that your computer can no longer do remote attestations. So you can no longer convince any 3rd parties that your computer is operating in a “secure” mode.

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JohnFen 963 days ago
> The only thing you can’t do with them (by design) is read the signing keys

That's why it makes me nervous.

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