Comment by mschuster91 | Hacker News Reader

Comment by mschuster91 | Hacker News Reader

Parent Full thread

> If your threat model is Iran

Well... they wouldn't be the first ones to black out the Internet either. And I'm not just talking about threats specific to oneself here because that is a much different threat model, but the effects of being collateral damage as well. Say, your country's leader says something that makes the US President cry - who's to say he doesn't order SpaceX to disable Starlink for your country? Or that Russia decides to invade yet another country and disables internet satellites [1]?

And it doesn't have to be politically related either, say that a natural disaster in your area takes out everything smarter than a toaster for days if not weeks [2].

> If your BIOS or bootloader is compromised then so is your OS.

well, that's the point of the TPM design and Secure Boot: that is not true any more. The OS can verify everything being executed prior to its startup back to a trusted root. You'd need 0-day exploits - while these are available including unpatchable hardware issues (iOS checkm8 [3]), they are incredibly rare and expensive.

[1] https://en.wikipedia.org/wiki/Viasat_hack

[2] https://www.telekom.com/de/blog/netz/artikel/lost-place-und-...

[3] https://theapplewiki.com/wiki/Checkm8_Exploit

> Say, your country's leader says something that makes the US President cry - who's to say he doesn't order SpaceX to disable Starlink for your country?

Then you tether to your phone or visit the local library or coffee shop and use the WiFi, or call into the system using an acoustic coupler on an analog phone line or find a radio or build a telegraph or stand on a tall hill and use flag semaphore in your country that has zero cell towers or libraries, because you only have to transfer a few hundred bytes of protocol overhead and 32 bytes of actual data.

At which point you could unlock your laptop, assuming it wasn't already on when you lost internet, but it still wouldn't have internet.

> The OS can verify everything being executed prior to its startup back to a trusted root.

Code that asks for the hashes and verifies them can do that, but that part of your OS was replaced with "return true;" by the attacker's compromised firmware.

The boot verification code wasn't replaced, because it sits in the encrypted partition.

That's premised on the attacker never having write access to the encrypted partition, which is the thing storing the FDE key on a remote system or removable media does better than a TPM. If the key is in a TPM and they can extract it using a TPM vulnerability or specialized equipment. Or boot up the system and unlock the partition by running the original signed boot chain, giving the attacker the opportunity to compromise the now-running OS using DMA attacks, cold-boot attacks, etc. Or they can stick it in a drawer without network access to receive updates until someone publishes a relevant vulnerability in the version of the OS that was on it when it was stolen.

Notice that if they can modify/replace the device without you noticing then they can leave you one that displays the same unlock screen as the original but sends any credentials you enter to the attacker. Once they've had physical access to the device you can't trust it. The main advantage of FDE is that they can't read what was on a powered off device they blatantly steal, and then the last thing you want is for the FDE key to be somewhere on the device that they could potentially extract instead of on a remote system or removable media that they don't have access to.

Reply on news.ycombinator.com