7 ms·

This isn't just one of many possible modes, it is automatically enabled on pretty much every new Windows laptop. I used to work on BitLocker so I'm biased, bu

This isn't just one of many possible modes, it is automatically enabled on pretty much every new Windows laptop. I used to work on BitLocker so I'm biased, but it's not pointless at all. If the hardware configuration, firmware, bootloader, boot settings, etc. are unchanged, as measured by Secure Boot and then each subsequent boot component, the TPM releases the key and automatically unlocks the drive. From that point forward, security depends on OS-level authentication and authorization. Even assuming poor hardware-level security, this will still protect against the only reasonable threat faced by most people: access to private data by device thieves or physical intruders. If you are in the tiny minority that actually wants to protect yourself against sophisticated actors who have exploits for the OS-level security, or the ability to extract keys from a running system or with a cold boot attack, you will want to be selective about your hardware and you might want to additionally rely on a PIN, password, or dongle in conjunction with the TPM/SecureBoot protection.

upofadown 9y ago
The interesting thing about whole disk encryption is that it is not really breakable if a reasonably long password/phrase is used. Using a TPM adds a huge attack surface for no practical reason. A large enough attack surface in this case that it is almost for sure going to be broken. The user only is going to be entering the password/phrase once per boot. Things are different in the case of something like a phone. In that case you are pretty much forced to use some low entropy key that could otherwise be brute forced. Then a secure hardware device makes sense, particularly if the phone does not use the device for everything but the kitchen sink as in this case.
- mjg59 9y ago
  There's a huge practical benefit - the user gains disk encryption without having to remember a secure passphrase. That's a big deal.
  - marcoperaza 9y ago
    Exactly and to elaborate, it means that the only secret a user needs to remember is a short PIN for OS-level authentication. The TPM's protection against modified boot and OS components make a brute force very difficult. Further, Windows will actually feed that PIN to the TPM for purposes of OS-level authentication, which leverages the TPM's enforcement of rate limits and lockouts in addition to OS-level implementations of those protections. A nice improvement would be to use a PIN entered at boot for purposes of drive decryption and then automatically pass it through to the OS-level login.
  - cm2187 9y ago
    And for a server it enables to reboot autonomously while protecting you from someone pulling a hard drive from the array (think server colocation).
- brians 9y ago
  It sounds like your threat model doesn’t interactive hardware adversaries. Mine does, so worry about how they might capture my long pass phrase is a big concern. Well, to whom do I tell my long passphrase? Right: my computer. Every morning. Is it running the same software as last night, no keyloggers, etc? That’s what the TPM is for.
Nullabillity 9y ago
And how are users supposed to recover their data when your system fails, and they have no idea what the key is?
- acqq 9y ago
  For Bitlocker it was necessary to print the key after it was generated and keep it somewhere because even some software updates and reboots could get you a screen where you had to type many many numbers and letters -- you could not use some password of yours there. Which wasn't pleasant. That meant that if you wanted to travel you had to have the printed key with you, or at such reboots at least phone somebody to who you have given that key. Which isn't a problem in an organization, were that somebody are the admins, who were those who made the keys before they gave you the notebook. I don't know how it works currently, if MS invented something more convenient recently.
  - zaarn 9y ago
    You can recover using your Live Account, which contains a copy of the key. But you still have to type it in. I do this regularly as a recent W10 upgrade broke the SoftTPM in my Ryzen CPU (no longer recognised at boot), so I type it in everytime I boot windows (so once or three times a month). It's very resilient since it has a built-in Error Detection Code for each 6 digit pair entered, if you make a typo, it likely will immediately complain and prevents entering any more of the code.
    - marcoperaza 9y ago
      You should use the manage-bde cli tool, or the bitlocker GUI, to remove the TPM protector and replace it with a passphrase. You’ll need to set one of the group policy options to enable using a passphrase.
      - zaarn 9y ago
        Yeah but I don't want that. I want to use the TPM, Windows just broke it. For the few times in the month where I need Windows, it's not worth the effort.

upofadown 9y ago

The interesting thing about whole disk encryption is that it is not really breakable if a reasonably long password/phrase is used. Using a TPM adds a huge attack surface for no practical reason. A large enough attack surface in this case that it is almost for sure going to be broken. The user only is going to be entering the password/phrase once per boot. Things are different in the case of something like a phone. In that case you are pretty much forced to use some low entropy key that could otherwise be brute forced. Then a secure hardware device makes sense, particularly if the phone does not use the device for everything but the kitchen sink as in this case.

mjg59 9y ago
There's a huge practical benefit - the user gains disk encryption without having to remember a secure passphrase. That's a big deal.
- marcoperaza 9y ago
  Exactly and to elaborate, it means that the only secret a user needs to remember is a short PIN for OS-level authentication. The TPM's protection against modified boot and OS components make a brute force very difficult. Further, Windows will actually feed that PIN to the TPM for purposes of OS-level authentication, which leverages the TPM's enforcement of rate limits and lockouts in addition to OS-level implementations of those protections. A nice improvement would be to use a PIN entered at boot for purposes of drive decryption and then automatically pass it through to the OS-level login.
- cm2187 9y ago
  And for a server it enables to reboot autonomously while protecting you from someone pulling a hard drive from the array (think server colocation).
brians 9y ago
It sounds like your threat model doesn’t interactive hardware adversaries. Mine does, so worry about how they might capture my long pass phrase is a big concern. Well, to whom do I tell my long passphrase? Right: my computer. Every morning. Is it running the same software as last night, no keyloggers, etc? That’s what the TPM is for.

Nullabillity 9y ago

And how are users supposed to recover their data when your system fails, and they have no idea what the key is?

acqq 9y ago
For Bitlocker it was necessary to print the key after it was generated and keep it somewhere because even some software updates and reboots could get you a screen where you had to type many many numbers and letters -- you could not use some password of yours there. Which wasn't pleasant. That meant that if you wanted to travel you had to have the printed key with you, or at such reboots at least phone somebody to who you have given that key. Which isn't a problem in an organization, were that somebody are the admins, who were those who made the keys before they gave you the notebook. I don't know how it works currently, if MS invented something more convenient recently.
- zaarn 9y ago
  You can recover using your Live Account, which contains a copy of the key. But you still have to type it in. I do this regularly as a recent W10 upgrade broke the SoftTPM in my Ryzen CPU (no longer recognised at boot), so I type it in everytime I boot windows (so once or three times a month). It's very resilient since it has a built-in Error Detection Code for each 6 digit pair entered, if you make a typo, it likely will immediately complain and prevents entering any more of the code.
  - marcoperaza 9y ago
    You should use the manage-bde cli tool, or the bitlocker GUI, to remove the TPM protector and replace it with a passphrase. You’ll need to set one of the group policy options to enable using a passphrase.
    - zaarn 9y ago
      Yeah but I don't want that. I want to use the TPM, Windows just broke it. For the few times in the month where I need Windows, it's not worth the effort.