[Cryptography] blockchain and trustworthy computing

[Ray Dillinger]

The problem with this is that if your block chain is restricted to
a single installation (vehicle) then it requires a trivial additional
expenditure in CPU onboard that vehicle to enable cheating.  So if
VW says, "and we're spending $10 per car on hashing power to prove
that this block chain thing is legit..."  but then actually installs
more or cheaper-per-hash hardware, or has understated the number of
hashes the hardware can do, then the car can produce fake block
chains on command that look just as good as the real one.

And this assumes customers are okay with the vehicle quickly running
its battery down continuing to hash all the time, whether running or
not, because if you allow it to quit hashing while it's not running,
then you allow a block chain to be faked by anything that can do
hashes while the car isn't doing any.

Also, what prevents a replacement block chain from being calculated
on much more capable hardware on demand and downloaded into the vehicle?

Finally, another problem with this is that even if you don't have the
capacity to fake a block chain built into the vehicle, what the block
chain in the vehicle shows at time B is whatever was put into it at
time A.  And the ability to prove at time B what was said at time A
has not much to do with proving that what was said at time A was true.

As Charles Babbage once said,

"I have been asked, 'Pray, Mr. Babbage, if you put into the machine
wrong figures, will the right answers come out?' I am not able rightly
to apprehend the kind of confusion of ideas that could provoke such a
question."

People talking about using Bitcoin's block chain to secure information
are relying on the property that Bitcoin's block chain would be very
very difficult for anybody to fake, because there is FIERCE competition
to get the next block and in order to fake it you'd have to get a bunch
of blocks in a row.

But this property simply isn't true for a small block chain that's
running in an isolated instance with a single "competitor" for the
blocks. Without independent agents fiercely competing for the next
block, you are left trusting the sole agent that is getting ALL the
blocks, which is not better than the situation you started with.

What you're proposing is essentially the same as a 'black box' that
just keeps a log of things indexed by time and mileage.  It being a
block chain wouldn't make it any harder to fake than a good tamper-
proof seal on a hardware black box.

				Bear

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