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Comment by jansommer

I think you get the biggest advantage from BitLocker when you use TPM (PCR 7+11) with a PIN. That should mitigate the exploit because the FVEK should never be read without the PIN, and if BitLocker does it right (which I think it does) too many wrong PIN's results in the TPM going into dictionary attack lockout mode.

Now I've been trying for months to do the same for Linux. There's systemd-cryptsetup/cryptenroll, but it's only for LUKS and I'm trying to encrypt a few sensitive directories on a super slow internal eMMC with fscrypt (keys for secure boot and /home). The TPM is _EXTREMELY_ hard to code for when things go beyond the basics:

1. Bind to PCR 7

2. Bind to changing PCR 11 (changes whenever the kernel, init, cmdline etc. is updated)

3. Use a PIN - but not the AuthValue, because I want to use the same authorization policy for resetting the DA lockout counter on login, and also have a long password/AuthValue for resetting the counter manually.

4. Make it all work with PCR 11 signatures and public keys provided by systemd-stub.

Maybe this isn't the right place to ask, but there's almost nothing but basic TPM guides out there, so if you're an expert I could really use your help. It's just for a personal project, but I'll write about it once I'm done - if I ever figure it out!

parent jansommer 1 year ago

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