Just update the microcode (was: Re: defending against evil in all layers of hardware and software)

[Sebastian Krahmer]

The "signature" in the microcode update has not the same
meaning as within crypto. For intel chips it has 31bits and basically
contains a revision number. The requirements for the BIOS for
checking microcode updates are in short: check the crc and ensure
that older revisions cant replace new ones by comparing the "signature".
I did not try myself, but I think one can probably update anything
if you just hexedit the update header.
Afaik these chips do not own any crypto-related functionallity
or storage capability (except precise timing and rand maybe) and
they are not tamper-proof. Thats why TPM was invented :-)

l8er,
Sebastian

On Mon, Apr 28, 2008 at 06:16:12PM -0400, John Ioannidis wrote:

> Intel and AMD processors can have new microcode loaded to them, and this 
> is usually done by the BIOS.  Presumably there is some asymmetric crypto 
> involved with the processor doing the signature validation.
> 
> A major power that makes a good fraction of the world's laptops and 
> desktops (and hence controls the circuitry and the BIOS, even if they do 
> not control the chip manufacturing process) would be in a good place to 
> introduce problems that way, no?
> 
> /ji
> 
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