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I'm curious if TPM measurements would catch these kind of manipulations. It's probably system specific but the configuration of the BIOS should (as far as I und
by TrueDuality 7y ago
I'm curious if TPM measurements would catch these kind of manipulations. It's probably system specific but the configuration of the BIOS should (as far as I understand it) be captured as part of the measurement process.
If requisite credentials or remote attestation is sealed against a certain measurement value it should protect the system.
- Avery3R 7y agoThe way locking a TPM to firmware config works is that the TPM has several registers called PCRs that contain a hash value. Anything can send data to the TPM and have it update the hash value, and you can lock TPM keys to the PCRs such that you can only use the key when the PCRs you choose have a specific value. The TCG spec defines some of these PCRs to be sent certain information [0], but it's up to the firmware to send it, the TPM doesn't magically know what the state is. If there's even a single setting or nvram variable that you can change to gain code execution that isn't part of the data that's sent to the PCRs that the crypto key is locked to, it's game over. [0]: https://trustedcomputinggroup.org/wp-content/uploads/TCG-EFI-Platform-Specification.pdf https://trustedcomputinggroup.org/wp-content/uploads/TCG-EFI...
- russfink 7y agoBIOS code is PCR 0, config is PCR 1. Software can "extend" certain PCRs as well. Look up Core Root of Trust for Measurement (CRTM) - lot of articles out there. BitLocker can use the capability you describe to protect the hard drive encryption keys. The TPM helps make sure the correct software is in control of the platform before releasing secrets.
- TACIXAT 7y agoIt helps but unless you are using the secure channel setup (no one is to my knowledge) attackers can intercept the PCRExtend operations and replace the data being extended.