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Comment by teddyh | Hacker News Reader

You could get almost the same benefits and none of the drawbacks of a TPM by using a password hash function with enough complexity to inherently limit the number of checks possible per second.

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I can't think of a key derivation function which would reliably make, say, a 6 digit PIN tough to crack while also not painfully impacting user experience waiting for the machine to unlock at boot. For a 6 digit PIN it's only 10 million iterations to exhaust all possible options, and the attacker gets to parallelize their guesses if they're willing to throw hardware or cloud resources at it.

I did say “almost”; one of the requirements is that you have to set an actually secure password; i.e. not a 6 digit PIN.

Totally! And for a user that knows the importance of a secure password, that's fine. But the average user in an organization picks terrible passwords. A random 5 or 6 digit PIN generated by the IT department (to avoid the user picking their daughter's birthday) used to lock a TPM is generally easy to remember and secure, especially if a lockout policy is set on the TPM.

I agree that for the user who would pick a secure passphrase, it's comparable security either way and thus really comes down to preference. I like tapping a quick PIN on the numpad rather than typing out a passphrase, but I can definitely see the advantages to the passphrase approach: you don't have to depend on a piece of hardware specific to the machine, and the attack surface for a potential backdoor is a lot smaller, especially if you're using FOSS full disk encryption software like Veracrypt.

> especially if a lockout policy is set on the TPM.

what happens at lockout?

Recovery with the escrow key held by IT, typically.

> For a 6 digit PIN it's only 10 million iterations to exhaust all possible options

Isn’t it one million?

Er... yep. Oops. That's embarassing, don't know how I made that mistake.

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