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Comment by mschuster91 | Hacker News Reader

Still pointless when the key can be sniffed in cleartext by intercepting the communication between the TPM and the CPU [1]. You should always combine it with something only known to the user (i.e. a passphrase).

The only attack TPM-backed disk encryption prevents is someone imaging the disk.

[1] https://blog.scrt.ch/2021/11/15/tpm-sniffing/

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…or booting from alternate media to retrieve data from the disk in situ (depending on which measurements are used to seal the key in the TPM).

“Don’t let perfect be the enemy of good.” Vulnerabilities/limitations should be understood and you have every right to determine that TPM+PIN is the minimum control that addresses threats you’ve modeled and reduces risk to a tolerable level, but TPM-only encryption is not pointless. It reduces risk by increasing required attack complexity without impacting usability. That’s enough for a lot of people.

> The only attack TPM-backed disk encryption prevents is someone imaging the disk.

The last section of the article you link says TPM 2.0 may fix the sniffing attack. It’s also worth noting that “someone imaging the disk” was really easy if you got even fairly brief access to the computer, whereas the other attacks that may still be viable involve invasive surgery and specialised knowledge of the hardware in question.

(This is my understanding as a developer not particularly informed about boot arrangements, upon reading some relevant material. I could be wrong or have missed some nuance.)

> The last section of the article you link says TPM 2.0 may fix the sniffing attack

English is not my native language but, as far as i know, _may_ expresses uncertainity.

> You should always combine it with something only known to the user (i.e. a passphrase).

The fact this isn't mandatory blows me away. I remember when my work machine first got TPM full disk encryption, a passphrase was needed.

A few years later? Meh. Who needs "real" security.

Of course I get it is a convenience trade off, it almost always is.

It's especially because Microsoft doesn't want to deal with people who manage to forget their unlock code or those who die without having a break-glass kit deposited at a bank locker, leaving their relatives in quite the mess.

I get it, for everyday people TPM-only is enough, but anyone remotely security-minded (or anyone traveling to the US and thus subject to the whims of the CBP) is better served with a good passphrase.

If CBP wants to know what's inside your laptop, and you're not an American citizen, your options are to show them or go back to where you came from, and possibly never be allowed back again. Missing a passphrase may mean you're not even presented with this option, though in principle you still should be asked even if the device were completely unlocked and unencrypted, but few would take the second option anyway, so for the majority of travellers, the passphrase is not really extra protection.

It's proven sufficient to show them what they expect to see.

Variations on plausibly deniable rubberhose | TrueCrypt bare metal vmhosts allow for parallel OS's - one that can be booted by default and be "family friendly" with all the apps and photos | IMs etc expected and another (or many) OS's that have non obvious triggers to allow for passphrase entry into journalists document vaults.

The evidence for parallel OS's is two fold:-

* non obvious drivers almost always overlooked and essentially never noticed in border patrol scans, and

* "unused" areas of drive storage with contents indistinguishable from white noise (or multi pass disk shredding).

That is a while extra level above what was being suggested.

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