5 ms·

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 m

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.

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.