Re: SHA-1 MBR

[Isaac Dupree]

Jan Alsenz wrote:
> Yes, that was my point. You need a trusted first step.
> But the only thing besides a TPM, that can be used for this is the BIOS,
> which can be flashed.
> And even, if we assume, that we can construct a BIOS that only boots if the
> MBR hash matches and can not be flashed prior to this point, there are
> still two points missing:
> - After the system has started, the BIOS could be flashed. This is a very
> possible scenario in a multi user environment.
> - They could take out the disk and put it in another machine, tamper with
> the boot code and switch it on. And all your protection is gone.
>   Ok, you could try to put a needed key in the BIOS too, but then we're
> back to problem one - and the BIOS can not check if a request for the key
> is valid. I'm not even sure, if something in the BIOS can be read
> protected.

BIOS could be in ROM, un-flashable, including hash/keys and all!  Refuse to 
boot if the hash doesn't match!  Admittedly this poses some limitations on 
whether the system can be upgraded, depending how sophisticated you want to 
be.