| ▲ | dist-epoch 3 days ago |
| > Active physical interposer adversaries are a very real part of legitimate threat models. You need an integrated root-of-trust in your CPU in order to solve these. It's been almost 10 years since Microsoft, based on their Xbox experience, started saying "stop using discrete TPMs over the bus, they are impossible to secure, we need the TPM embedded in the CPU itself" |
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| ▲ | Tharre 2 days ago | parent | next [-] |
| The TPM itself can actually be discrete, as long as you have a root-of-trust inside the CPU with a unique secret. Derive a secret from the unique secret and the hash of the initial bootcode the CPU is running like HMAC(UDS, hash(program)) and derive a public/private key pair from that. Now you can just do normal Diffie-Hellman to negotiate encryption keys with the TPM and you're safe from any future interposers. This matters because for some functionality you really want tamper-resistant persistent storage, for example "delete the disk encryption keys if I enter the wrong password 10 times". Fairly easy to do on a TPM that can be made on a process node that supports flash vs a general CPU where that just isn't an option. |
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| ▲ | RobotToaster 3 days ago | parent | prev [-] |
| That's assuming you trust the CPU vendor not to have their own interposer. |
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| ▲ | dist-epoch 3 days ago | parent [-] | | If you don't trust the CPU vendor in your machine you have bigger problems. | | |
| ▲ | RobotToaster 3 days ago | parent | next [-] | | Given that the Intel ME and AMD PSP are both backdoors, we all have problems. | | |
| ▲ | ahoka a day ago | parent | next [-] | | It’s only a backdoor if it’s undocumented. | |
| ▲ | commandersaki 2 days ago | parent | prev [-] | | Who has the keys to this backdoor? [for the curious] | | |
| ▲ | immibis 2 days ago | parent [-] | | At a minimum, Intel and AMD. | | |
| ▲ | commandersaki 2 days ago | parent [-] | | What kind of keys are they? In that same regard, Apple holds the keys to sign software for secure enclaves on iDevices and Macs, does that make them backdoored, since they can control execution on the firmware that protects everyone's authentication data and secrets? | | |
| ▲ | immibis 2 days ago | parent [-] | | Yes, Apple products are backdoored - not just through esoteric keys, but also because they're uploading your pictures to the mothership "to check they're not hild porn." | | |
| ▲ | commandersaki 2 days ago | parent [-] | | because they're uploading your pictures to the mothership "to check they're not hild porn." Citation needed. Also, if virtually every software that is updateable by a vendor, then going by your argument, everything is a backdoor. Not a very useful term then. |
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| ▲ | LtWorf 3 days ago | parent | prev [-] | | Yes we do have those big problems. |
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