alt Hacker NewsIt all weird still
Suppose the physical attacker doesn't reset the bios. He boots Ubuntu or any other os which is signed. Will the tpm unlock and give out the key? I guess it depends on the setup and it's possible to unlock only on your own signed kernel but I doubt this is a default?
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At which point they will be stopped by Ubuntu login screen which requires user password (or fingerprint, pin, etc).
Basically there are two options for have to enter 1 password: 1. TPM disk encryption + login password. 2. Password for disk encryption and automatic login (doesn't support multiple user accounts well).
I think this is like the windows bit locker vulnerability that was seen a while ago.
The windows recovery put the TPM in the same state as the normal windows OS, so it released bit locker keys, but you could bypass the login on the recovery environment.
The keys can be indirectly sealed against specific system and software configurations such that this attack is not possible. Additionally, as you noted, using custom secure boot keys would prevent the attacker from booting an arbitrary OS.