Questions about checking free hardware

[xdrudis at tinet.cat]

On Fri, Sep 18, 2015 at 07:32:14PM +0200, Paul Hänsch wrote:
> 
> Or maybe you can image them in some kind of MRI...? Then you could at 
> least match your chip against the image of a prototype. Can a 
> microprocessor survive the MRI process? Are MRI resolutions high enough 
> to make the structures visible, at least for past generation chips? Are 
> the materials in the processor suitable to produce a clear image?
> 

I don't know, but I think people take X-ray images of chips or
something similar, to investigate security, manipulations or QA in
factories or something.

In any case I don't think it would be practical. 

When everything is software you can try repeatable builds (or more
traditionally you can just do your own build and discard the binary
you suspect). But that is because you can produce the object from the
source. In hardware you can't produce the circuit from the design 
if you don't have a factory, and even if you had some form of repeteable
builds for hardware, you'd still need advanced machinery to check 
a sample is similar enough to your repeteable build. I don't know
whether the infrastructure for manufacturing would be more expensive 
or less that the infrastructure for verification, but I believe
any of them would be too expensive and so complex that the 
"reflections on trusting trust"[1] by Ken Thompson 
would likely apply mutatis mutandis. 

In fact we would need both open hardware and affordable hardware
factories. But, hey, open hadware is a great start and a necessity 
even if you can't build a fab in your garage. 


[1] http://www.win.tue.nl/~aeb/linux/hh/thompson/trust.html
https://www.schneier.com/blog/archives/2006/01/countering_trus.html
etc.

-- 
Xavi Drudis Ferran