4 ms·

It's an important topic, but the basic tradeoffs with TPMs and HSMs are that either you, a) trust the vendor is generating root secrets with sufficient entropy,

It's an important topic, but the basic tradeoffs with TPMs and HSMs are that either you, a) trust the vendor is generating root secrets with sufficient entropy, whether they are a private key or a symmetric secret, b) you trust the personalization process for replacing the OEM secrets with personalized ones, or c) you trust the firmware to not yield the unique secrets you generate in it. There are issues with all of these, but it's a question of in which security context you are generating your root secrets and keys. e.g. at manufacture, at personalization, or whenever the end user wants to. The catastrophic failure mode of TPM's depending on shared root secrets may actually be a privacy feature, imo, because in all the digital identity work I have done, this was where every scheme fell over.

hsbauauvhabzb 3y ago
Even if flawed, it can still act as a safety in numbers game. You have to be able to abuse TPM and be in a position to do so, in the context of fde, even a flawed tpm v1 approach stops 90% of potential threat actors capable of abusing an unencrypted device.
- motohagiography 3y ago
  A solution that was rarely implemented was batch keys, where your secrets installed by the OEM were diversified somehow so when attackers eventually extracted your TPM secrets from one device, it would not compromise all devices. It still has a terrible and unacceptable failure mode when peoples lives depend on it, but for infrastructure, I think the risk is more managable.
  - hsbauauvhabzb 3y ago
    If your threat model involves people sniffing TPM signals in transit, you’re in a different league to me. In most cases I assume physical security (security guards, epoxy the motherboard, etc) become the mitigating factors. I’m just trying to avoid evil maids.
    - loup-vaillant 3y ago
      Making an TPM genie isn’t that hard, and once we have that the Evil Maid can fairly easily unplug the discrete TPM, plug the Genie, and plug the TPM into the genie. And voilà, you can now sniff TPM signals in transit. Only works with discrete TPMs of course, but Man-in-the-Middle is not out of this world. https://github.com/nccgroup/TPMGenie https://github.com/nccgroup/TPMGenie
      - hsbauauvhabzb 3y ago
        I’m more referring to laptops. If you’re using a desktop, you also have other issues (like key injectors unless you inspect the cable going from your pc to your desk every time, etc).

hsbauauvhabzb 3y ago

Even if flawed, it can still act as a safety in numbers game. You have to be able to abuse TPM and be in a position to do so, in the context of fde, even a flawed tpm v1 approach stops 90% of potential threat actors capable of abusing an unencrypted device.

motohagiography 3y ago
A solution that was rarely implemented was batch keys, where your secrets installed by the OEM were diversified somehow so when attackers eventually extracted your TPM secrets from one device, it would not compromise all devices. It still has a terrible and unacceptable failure mode when peoples lives depend on it, but for infrastructure, I think the risk is more managable.
- hsbauauvhabzb 3y ago
  If your threat model involves people sniffing TPM signals in transit, you’re in a different league to me. In most cases I assume physical security (security guards, epoxy the motherboard, etc) become the mitigating factors. I’m just trying to avoid evil maids.
  - loup-vaillant 3y ago
    Making an TPM genie isn’t that hard, and once we have that the Evil Maid can fairly easily unplug the discrete TPM, plug the Genie, and plug the TPM into the genie. And voilà, you can now sniff TPM signals in transit. Only works with discrete TPMs of course, but Man-in-the-Middle is not out of this world. https://github.com/nccgroup/TPMGenie https://github.com/nccgroup/TPMGenie
    - hsbauauvhabzb 3y ago
      I’m more referring to laptops. If you’re using a desktop, you also have other issues (like key injectors unless you inspect the cable going from your pc to your desk every time, etc).