7 ms·

The real question is "What's your threat model?" If it's people stealing your laptop and fear of identity theft, use the TPM. If it's the NSA, ¯\_(ツ)_/¯

cobertos 3y ago
LUKS or eCryptfs work perfectly fine for the "stealing your laptop" use case, and are purely software implementations. There's a poster below that provides a more reasonable use case for TPM. Headless server where asking for password on boot is undesirable (eg after a power failure)
- Nextgrid 3y ago
  Only problem of software implementations is that they are reliant on the strength of the user-supplied passphrase, so there's a inverse correlation between user experience (ease of typing the passphrase) and security (easy passphrases are also easy to bruteforce). A TPM provides hardware-backed bruteforce protection which means even an easy passphrase can be made secure as the number of attempts is rate-limited by the TPM (to a level much slower than even the hardest hashes).
  - immibis 3y ago
    Then you want your own optional TPM that you trust - such as a YubiKey.
    - mjg59 3y ago
      Why is a Yubikey more trustworthy? You don't have the source code, you don't have the hardware design. In addition, a Yubikey is given no information about the system boot state, so is in no position to identify that the system has been tampered with.
      - immibis 3y ago
        It's just one example. Use a different one if you want. People tend to trust them more because they belong to them, not Microsoft, or Hollywood, or the board manufacturer.
        mkopec 3y ago
        In what manner specifically does a TPM not belong to the user, while a YubiKey does?
        immibis 3y ago
        Yubikey gets paid by people who want to do security things. Board manufacturers get paid, indirectly, by Microsoft allowing their boards to run Windows. The incentives are different.
    - Nextgrid 3y ago
      The advantage of a TPM embedded in the platform is that it is aware of the platform's state - the hashes of the firmware, option ROMs and the bootloader/UEFI binary that you're loading. Discrete TPMs are vulnerable to bus interception attacks but newer firmware TPMs are embedded in the CPU/SoC and are invulnerable to this so it's pretty secure. A YubiKey/external TPM in comparison has no way to know whether it's being fed true PCR readings from the host or fakes from a malicious attacker, so at this point it will be no different (in the context of full-disk-encryption) from just having a dumb USB storage device with your LUKS keyfile on it.
LikesPwsh 3y ago
Like most ordinary folks, my threat model is the use of TPM for DRM. Netflix playing at lower resolution for example. Widespread TPM is actively harmful for most people, and the biggest blow to general purpose computing in recent years.
- dist-epoch 3y ago
  > Netflix playing at lower resolution for example. Nobody is forcing you to use Netflix. If you don't like it, leave for a better DRM-free service. That's the free market at work.
  - yjftsjthsd-h 3y ago
    The alternatives also use DRM, because licensing means that it's not a free market.
    - kenjackson 3y ago
      Why does licensing mean it’s not a free market?
      - HideousKojima 3y ago
        It's not the licensing, but rather theat copyright is literally a government enforced monopoly on intellectual property that makes it not a free market.
        kenjackson 3y ago
        Thanks. That makes sense.
      - yjftsjthsd-h 3y ago
        Because the vast majority of content is owned by a tiny number of copyright owners (studios, IIRC, but it doesn't really matter who, just how many), who then impose artificial constraints. Netflix didn't decide to implement DRM on its own, it passed through requirements that would be imposed on anyone else too.
rnhmjoj 3y ago
It doesn't need to be the NSA; if your chip is vulnerable and exploits published online I don't think it's too far fetched that a resourceful thief could try to unlock your disk if he thinks it has valuable content (bank accounts, cryptocurrency, passwords, etc.) Why take unnecessary risks when you can just use GRUB+LUKS and type the passphrase at boot?
- Nextgrid 3y ago
  GRUB+LUKS can also have exploits published online? If that happens, you upgrade to a newer version. TPM is the same - any known vulnerabilities would generally get patched as part of firmware updates released by your vendor. If the TPM is known vulnerable and a patch doesn't exist then fair enough you can stop using it depending on your threat model, but the same can be said for software implementations. > when you can just use GRUB+LUKS and type the passphrase at boot? This is a user experience drawback and opens you to other avenues of attack like passphrase bruteforce if you don't choose a strong (and inconvenient/slow to type) one. It's also impossible for servers or embedded devices which you want to be able to boot unattended.
  - rnhmjoj 3y ago
    > TPM is the same It's not really: LUKS is an open standard and GRUB is a free software that implements it. With a TPM you're likely to get a chip that is 100% a black box, with the exception of a few people who signed NDAs and researches that have knowledge and tools to poke into it. > generally get patched as part of firmware updates released by your vendor If it can even be fixed with a softwar update. Also, you're very lucky to get maybe a couple of years of firmware updates, then your're on your own.
    - Nextgrid 3y ago
      > with the exception of a few people who signed NDAs and researches that have knowledge and tools to poke into it. This is good enough for the 90% of people who currently operate without full-disk-encryption at all. It would be a huge improvement. Obviously, it's up to each individual user to evaluate their threat model and proceed accordingly. Nobody is forcing you to use a TPM, you can still use LUKS/etc and completely ignore the TPM.
SenpaiSilver 3y ago
How is the TPM protecting my if my laptop with the TPM chip is stolen? I understand that I will be protected from removing the HDD/SSD and putting it into another machine to read the data, but does it really protect me from anything else?
- mjg59 3y ago
  Preventing your storage from being put in another device is what it's meant to be protecting you against. If it's still in the original device then an attacker is still blocked by your login password.
- sokoloff 3y ago
  What other protections might you expect it to provide? Being unable to retrieve the data on protected drives (which could include cookies, passwords, ID, photos/videos, etc.) is the value.
huggingmouth 3y ago
No, the true question is why should we switch to tpms, and what are we giving up if we do. In my experience, tpms are worse than worthless since they prevent rescuing garddrives from bricked systems. Nontpm luks can be unlocked on any system.
- Nextgrid 3y ago
  You can enroll a backup key if your full-disk-encryption system supports it. Both LUKS and Bitlocker do, so the TPM key can be one of many (the second one being a backup key stored away securely). It'll only prevent you from recovering a hard drive if you configured it that way - ie it's doing its job as designed.
Bognar 3y ago
I'm always curious what threat model that is valid against TPMs is not also valid against CPUs and main memory.
traverseda 3y ago
Or anyone with a pcileach.

cobertos 3y ago

LUKS or eCryptfs work perfectly fine for the "stealing your laptop" use case, and are purely software implementations. There's a poster below that provides a more reasonable use case for TPM. Headless server where asking for password on boot is undesirable (eg after a power failure)

Nextgrid 3y ago
Only problem of software implementations is that they are reliant on the strength of the user-supplied passphrase, so there's a inverse correlation between user experience (ease of typing the passphrase) and security (easy passphrases are also easy to bruteforce). A TPM provides hardware-backed bruteforce protection which means even an easy passphrase can be made secure as the number of attempts is rate-limited by the TPM (to a level much slower than even the hardest hashes).
- immibis 3y ago
  Then you want your own optional TPM that you trust - such as a YubiKey.
  - mjg59 3y ago
    Why is a Yubikey more trustworthy? You don't have the source code, you don't have the hardware design. In addition, a Yubikey is given no information about the system boot state, so is in no position to identify that the system has been tampered with.
    - immibis 3y ago
      It's just one example. Use a different one if you want. People tend to trust them more because they belong to them, not Microsoft, or Hollywood, or the board manufacturer.
      - mkopec 3y ago
        In what manner specifically does a TPM not belong to the user, while a YubiKey does?
        immibis 3y ago
        Yubikey gets paid by people who want to do security things. Board manufacturers get paid, indirectly, by Microsoft allowing their boards to run Windows. The incentives are different.
  - Nextgrid 3y ago
    The advantage of a TPM embedded in the platform is that it is aware of the platform's state - the hashes of the firmware, option ROMs and the bootloader/UEFI binary that you're loading. Discrete TPMs are vulnerable to bus interception attacks but newer firmware TPMs are embedded in the CPU/SoC and are invulnerable to this so it's pretty secure. A YubiKey/external TPM in comparison has no way to know whether it's being fed true PCR readings from the host or fakes from a malicious attacker, so at this point it will be no different (in the context of full-disk-encryption) from just having a dumb USB storage device with your LUKS keyfile on it.

LikesPwsh 3y ago

Like most ordinary folks, my threat model is the use of TPM for DRM. Netflix playing at lower resolution for example. Widespread TPM is actively harmful for most people, and the biggest blow to general purpose computing in recent years.

dist-epoch 3y ago
> Netflix playing at lower resolution for example. Nobody is forcing you to use Netflix. If you don't like it, leave for a better DRM-free service. That's the free market at work.
- yjftsjthsd-h 3y ago
  The alternatives also use DRM, because licensing means that it's not a free market.
  - kenjackson 3y ago
    Why does licensing mean it’s not a free market?
    - HideousKojima 3y ago
      It's not the licensing, but rather theat copyright is literally a government enforced monopoly on intellectual property that makes it not a free market.
      - kenjackson 3y ago
        Thanks. That makes sense.
    - yjftsjthsd-h 3y ago
      Because the vast majority of content is owned by a tiny number of copyright owners (studios, IIRC, but it doesn't really matter who, just how many), who then impose artificial constraints. Netflix didn't decide to implement DRM on its own, it passed through requirements that would be imposed on anyone else too.

rnhmjoj 3y ago

It doesn't need to be the NSA; if your chip is vulnerable and exploits published online I don't think it's too far fetched that a resourceful thief could try to unlock your disk if he thinks it has valuable content (bank accounts, cryptocurrency, passwords, etc.) Why take unnecessary risks when you can just use GRUB+LUKS and type the passphrase at boot?

Nextgrid 3y ago
GRUB+LUKS can also have exploits published online? If that happens, you upgrade to a newer version. TPM is the same - any known vulnerabilities would generally get patched as part of firmware updates released by your vendor. If the TPM is known vulnerable and a patch doesn't exist then fair enough you can stop using it depending on your threat model, but the same can be said for software implementations. > when you can just use GRUB+LUKS and type the passphrase at boot? This is a user experience drawback and opens you to other avenues of attack like passphrase bruteforce if you don't choose a strong (and inconvenient/slow to type) one. It's also impossible for servers or embedded devices which you want to be able to boot unattended.
- rnhmjoj 3y ago
  > TPM is the same It's not really: LUKS is an open standard and GRUB is a free software that implements it. With a TPM you're likely to get a chip that is 100% a black box, with the exception of a few people who signed NDAs and researches that have knowledge and tools to poke into it. > generally get patched as part of firmware updates released by your vendor If it can even be fixed with a softwar update. Also, you're very lucky to get maybe a couple of years of firmware updates, then your're on your own.
  - Nextgrid 3y ago
    > with the exception of a few people who signed NDAs and researches that have knowledge and tools to poke into it. This is good enough for the 90% of people who currently operate without full-disk-encryption at all. It would be a huge improvement. Obviously, it's up to each individual user to evaluate their threat model and proceed accordingly. Nobody is forcing you to use a TPM, you can still use LUKS/etc and completely ignore the TPM.

SenpaiSilver 3y ago

How is the TPM protecting my if my laptop with the TPM chip is stolen? I understand that I will be protected from removing the HDD/SSD and putting it into another machine to read the data, but does it really protect me from anything else?

mjg59 3y ago
Preventing your storage from being put in another device is what it's meant to be protecting you against. If it's still in the original device then an attacker is still blocked by your login password.
sokoloff 3y ago
What other protections might you expect it to provide? Being unable to retrieve the data on protected drives (which could include cookies, passwords, ID, photos/videos, etc.) is the value.

huggingmouth 3y ago

No, the true question is why should we switch to tpms, and what are we giving up if we do. In my experience, tpms are worse than worthless since they prevent rescuing garddrives from bricked systems. Nontpm luks can be unlocked on any system.

Nextgrid 3y ago
You can enroll a backup key if your full-disk-encryption system supports it. Both LUKS and Bitlocker do, so the TPM key can be one of many (the second one being a backup key stored away securely). It'll only prevent you from recovering a hard drive if you configured it that way - ie it's doing its job as designed.

Bognar 3y ago

I'm always curious what threat model that is valid against TPMs is not also valid against CPUs and main memory.

traverseda 3y ago

Or anyone with a pcileach.