Is Bitlocker secure against theft even if the TPM is hacked (assuming the machine is hibernating)?

Question

Does Bitlocker encrypt the drive only with the Bitlocker recovery key, or does it also encrypt the drive with the Windows login password (so that the attacker would need to guess the login password as well, which would be infeasible for a very complex one) - obviously this describes cases where other forms of login like PIN and smart card is disabled.

Background:

Apparently it's possible for a well funded attacker to extract cryptographic keys from a TPM. Obviously this would only be a realistic threat if the system held many millions of dollars worth of information, but it's still a threat to many large companies that allow their employees to take work computers outside the office.

EDIT: This assumes outright theft of the computer, as opposed to an evil maid attack (otherwise the attacker could just use a keylogger or something)

Answer 1

First of all, to the comment by André, from what I understand, full disk encryptions are exactly for the case of an attacker gaining full physical access to the hardware, like in the case of a (notebook) theft.

As for the rest: a hybernating computer should be vulnerable.

This is after some research the best article on the topic: https://securingtomorrow.mcafee.com/mcafee-labs/release-windows-10-questions-bitlocker-arise/ .

If the system is hibernating, it can be awoken again, and then any of the described attacks like "cold boot" should work.

Also, if the TPM gets hacked (though I am not sure if that is very realistic, or if there are known weaknesses in some TPMs) that would also be a bad thing.

Still, I think those attacks are no thread for everyday security, since their effort is fairly large, meaning that in most cases, no attackers would make those efforts unless there are reasonably high (information) rewards.

Answer 2

1. ASSUMING YOU USE TPM-ONLY PROTECTION (a bad assumption; don't do this), cracking the TPM will let a user decrypt the drive. The user's password is not, and cannot be, used to protect a BitLocker drive (too much of what Windows does happens before login). Individual files on the drive may be protected in other ways (for example, using Encrypting File System, which uses a key that your password is required to unwrap - though the attacker can attempt to brute-force the weak NTLMv2 password hashes to get it - or using something like VeraCrypt or GPG).
2. The security assumption in TPM-only mode is "attacker can boot the machine, but will by stymied at the login screen". So yes, in this mode, it is essential to use a strong login password. However, an attacker can still attempt various sophisticated attacks against the running system (BitLocker tries to block these as much as possible, but it can't do anything against, say, the RAM being frozen and physically removed from a running system).
3. If you want to actually be secure against an attack like this, BitLocker needs to be used in a mode that requires a "PIN" (misnomer; it can be an arbitrary passphrase unless your BIOS is very old) or external key (usually carried on USB flashdrive).