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0 pointsahepp9mo ago0 comments

I'm not sure I understand why secure boot is user-infantilizing? I think there are some legitimate concerns about where attestation could be headed, but I like the ability to force my machine to only run signed executables.

It seems like the immediate problem here is that most people will never enroll their own keys, and if every vendor's crappy EFI binary gets signed by Microsoft, there will be a huge library of garbage vendor code which is all an attack surface.

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AnthonyMouse9mo ago

The problem here is that the signature doesn't do anything for you.

Suppose you want to be assured of the software running on your machine. You go into the firmware, point it at your boot loader and say "only this one". It makes a hash of the boot loader and refuses to use any other one until you change the setting, which requires your firmware password. Your boot loader then only loads the operating systems you've configured, and so on.

That doesn't require any certificates and you get 100% of the benefits. The firmware needs to verify the boot loader and the boot loader the OS etc. The OS doesn't need to verify the firmware because it can't because if the firmware or boot loader was compromised then the code in the OS to validate it would be just as compromised.

The only thing the signature gets you is remote attestation, which is the evil to be prevented. Simple hashing would get you everything else.

And then you also don't get this "garbage code is nonetheless trusted" problem because there is no global root of trust and you never told your firmware to trust this random firmware update utility for somebody else's hardware.

mschuster919mo ago

> The problem here is that the signature doesn't do anything for you.

For your own personal machine, sure. But say you're a sysadmin in a company that has thousands of units. Suddenly, a CA infrastructure is much more appealing than having to deal with component hashes.

AnthonyMouse9mo ago

How is it any different? You install the hash of the boot loader when you issue the machine, then use the trusted system to update the hash if necessary.

Also, the concern is that the system comes from the factory with private keys the owner doesn't have access to, allowing the device to defect by informing on them to a third party. Keys installed by the owner rather than the manufacturer are fine, and then such keys also wouldn't be trusting random third party code either.

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gruez9mo ago

>Suppose you want to be assured of the software running on your machine. You go into the firmware, point it at your boot loader and say "only this one". It makes a hash of the boot loader and refuses to use any other one until you change the setting, which requires your firmware password. Your boot loader then only loads the operating systems you've configured, and so on.

What if you need to update the bootloader?

>The only thing the signature gets you is remote attestation, which is the evil to be prevented. Simple hashing would get you everything else.

TPMs can do remote attestation without signatures just fine, by measuring the hash of the bootloader. It'd be clumsy, but doable, just like your idea of using hashes for verification.

AnthonyMouse9mo ago

> What if you need to update the bootloader?

Then you boot the system from the existing bootloader, causing the booted system to be trusted to supply a new hash.

> TPMs can do remote attestation without signatures just fine, by measuring the hash of the bootloader.

If there are no private keys in the TPM from the factory then there is nothing for a third party to force you to sign the hash with, as intended.

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AnthonyMouse9mo ago

The problem here is that the signature doesn't do anything for you.

The only thing the signature gets you is remote attestation, which is the evil to be prevented. Simple hashing would get you everything else.

mschuster919mo ago

> The problem here is that the signature doesn't do anything for you.

AnthonyMouse9mo ago

How is it any different? You install the hash of the boot loader when you issue the machine, then use the trusted system to update the hash if necessary.

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gruez9mo ago

What if you need to update the bootloader?

>The only thing the signature gets you is remote attestation, which is the evil to be prevented. Simple hashing would get you everything else.

TPMs can do remote attestation without signatures just fine, by measuring the hash of the bootloader. It'd be clumsy, but doable, just like your idea of using hashes for verification.

AnthonyMouse9mo ago

> What if you need to update the bootloader?

Then you boot the system from the existing bootloader, causing the booted system to be trusted to supply a new hash.

> TPMs can do remote attestation without signatures just fine, by measuring the hash of the bootloader.

If there are no private keys in the TPM from the factory then there is nothing for a third party to force you to sign the hash with, as intended.

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