Re: Anti piracy: dummy components etc to fool copiers
From: N. Thornton (bigcat_at_meeow.co.uk)
Date: 11/13/04
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Date: 13 Nov 2004 15:12:47 -0800
Tom <Tom@notalotofpeopleknowthat.com> wrote in message news:<uFFaHpJgF+kBFwbn@furfur.demon.co.uk>...
> Thank you guys,
>
> an informative - and fun! - discussion. The thermite may not go down too
> well with some customers, and we can't afford some of the solutions, but
> there are some really good ideas there.
Bearing in mind your budget limitations:
A PCB with more than 2 layers
A bunch of very thin wire links with a single glob of potting compound
over the lot.
Use printed resistors on a layer inside the PCB
No IC markings at all - in which case ensure your design uses ICs all
with differing packages.
Dummy parts are too easy to work out
Run a track or 2 under the wrong IC, then out the other side to where
it really needs to go. May only be picked up if they desolder the
board.
A custom IC would be best, but I understand its beyond your budget.
Fill all spaces with tracks that do nothing useful. Use nice thin
densely populated tracks to make it look harder to follow them all.
This is psychologically offputting as much as anything.
Blob gloop over a small SMIC so it looks like a custom chip - just
might put them off trying. Add extra unuseful tracks to it to make it
look more complex. This can be seriously offputting if theyre not too
determined.
Another silly psychological tool is a false service data port, marked
as a real one, that gives out data in an easy format, but the data it
gives is an apparently real servicing message that implies youve put
time and effort into making this very hard for them to reverse
engineer.
Simple examples would be reporting things like 'select mode 1-4' or
referring to 'service mode' when theres only one mode, perhaps
offering what sounds like very useful info if only they can somehow
get it into service mode. Also, mentioning technologies that dont
exist or arent used, giving test routine instructions that destroy the
IC, referrring to this as an interim model, implying a new higher tech
model thats due to come out any day now, etc.
These psych tricks dont always make the circuit significantly harder
to figure out, but they do sometimes serve to put people off trying.
Trigger points: If youre using opamps and uprocs there is always the
option to have one or 2 obvious test points that sit there looking for
increased C or R on the test point: if a probe touches them they shut
down the circuit permanently, or for an annoying time like 2 weeks.
You could possibly do that destructively, all it takes is switching a
transistor to feed Vcc somewhere delicate, or reverse the rails on a
board stuffed with tants etc. Only consider this trick if the product
is assembled in such a way that the trigger test point can not become
touched with power applied, you dont want to introduce a significant
failure mode. That probably means a sealed box or compartment.
Finally just for interest, theres a method I used for this once that
worked a treat, but I dont recommend it. I used the biggest IC as the
PCB, sat it upside down and mounted all components directly onto it,
cutting all leads as short as poss. It was an utter mess, and trying
to trace anything anywhere was hopeless, you couldnt even physically
reach the conenctions. Solder wires to the nest and pot it. No use for
production runs, but it was ideal for that unusual case. It worked,
no-one managed to copy it.
>From what you've said I expect a fake custom IC blob with lots of
tracks should put them off. If you have a spare IO pin then a fake
service port might be simple to implement too.
NT
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