5 ms·

Best mitigation against this isn't mentioned, which would be to use a built-in firmware TPM (fTPM). The fTPM may have other issues, but it would be a lot harder

Best mitigation against this isn't mentioned, which would be to use a built-in firmware TPM (fTPM). The fTPM may have other issues, but it would be a lot harder to probe the signals!

xaduha 5y ago
MS allows to use smartcards for Bitlocker, with a caveat that it can't be used for a system disk, only TPM can be used for that which seems arbitrary. If there's an option to use TPM+PIN, then there should be an option to use smartcard+PIN.
- pgeorgi 5y ago
  > only TPM can be used for that which seems arbitrary. Smartcard readers can use any number of protocols (e.g. random USB readers implementing custom handshakes) until you finally get to the smartcard while TPMs have a select few number of protocols until you're talking to the TPM. Arbitrary smartcard terminal drivers in your (secure) preboot software? maybe not.
  - xaduha 5y ago
    Majority of modern readers are CCID compatible, limit it to that. libccid.so is 111KB, UsbccidDriver.dll is 81KB, I'm sure they would've managed if they wanted to. https://en.wikipedia.org/wiki/CCID_(protocol) https://en.wikipedia.org/wiki/CCID_(protocol)
- fomine3 5y ago
  Smartcard can't do self lockout at HW modification and other TPM features so not equivalent. Still, it should be able to use as additional key to password only BitLocker, but then maybe lack of Smartcard driver at UEFI is a blocker.
  - xaduha 5y ago
    It doesn't have to be an equivalent to be an option. Just like having no encryption is an option or auto-unlocking is an option. It's not like TPM detects that there are hardware changes, Windows itself does and it can lock it down. Or if there is some mechanism it doesn't seem to help in this case, so who is it stopping?
    - pgeorgi 5y ago
      TPMs are notified about the system state along the boot process, so they can present the key only if the boot process looks like it's supposed to (and some of these attributes aren't even modifiable by the CPU but the side processor, e.g. Intel's "Management" Engine or AMD's "Security" Processor, so even taking over the x86 firmware doesn't help anymore) Smartcards lack that data (they wouldn't know that somebody attached a Thunderbolt device that pretends to be a GPU but also comes with its own option ROM that installed a backdoor), so they serve a different threat model.
      - xaduha 5y ago
        And now the whole 'separate TPM' thing is obsolete, because newer processors will come with their own TPMs. This was a bad idea from the start if you ask me, with UEFI and shoving all sorts of things into it.

Best mitigation against this isn't mentioned, which would be to use a built-in firmware TPM (fTPM). The fTPM may have other issues, but it would be a lot harder to probe the signals!

xaduha 5y ago

MS allows to use smartcards for Bitlocker, with a caveat that it can't be used for a system disk, only TPM can be used for that which seems arbitrary. If there's an option to use TPM+PIN, then there should be an option to use smartcard+PIN.

pgeorgi 5y ago
> only TPM can be used for that which seems arbitrary. Smartcard readers can use any number of protocols (e.g. random USB readers implementing custom handshakes) until you finally get to the smartcard while TPMs have a select few number of protocols until you're talking to the TPM. Arbitrary smartcard terminal drivers in your (secure) preboot software? maybe not.
- xaduha 5y ago
  Majority of modern readers are CCID compatible, limit it to that. libccid.so is 111KB, UsbccidDriver.dll is 81KB, I'm sure they would've managed if they wanted to. https://en.wikipedia.org/wiki/CCID_(protocol) https://en.wikipedia.org/wiki/CCID_(protocol)
fomine3 5y ago
Smartcard can't do self lockout at HW modification and other TPM features so not equivalent. Still, it should be able to use as additional key to password only BitLocker, but then maybe lack of Smartcard driver at UEFI is a blocker.
- xaduha 5y ago
  It doesn't have to be an equivalent to be an option. Just like having no encryption is an option or auto-unlocking is an option. It's not like TPM detects that there are hardware changes, Windows itself does and it can lock it down. Or if there is some mechanism it doesn't seem to help in this case, so who is it stopping?
  - pgeorgi 5y ago
    TPMs are notified about the system state along the boot process, so they can present the key only if the boot process looks like it's supposed to (and some of these attributes aren't even modifiable by the CPU but the side processor, e.g. Intel's "Management" Engine or AMD's "Security" Processor, so even taking over the x86 firmware doesn't help anymore) Smartcards lack that data (they wouldn't know that somebody attached a Thunderbolt device that pretends to be a GPU but also comes with its own option ROM that installed a backdoor), so they serve a different threat model.
    - xaduha 5y ago
      And now the whole 'separate TPM' thing is obsolete, because newer processors will come with their own TPMs. This was a bad idea from the start if you ask me, with UEFI and shoving all sorts of things into it.