[Cryptography] blockchain and trustworthy computing

Peter Todd pete at petertodd.org
Fri Oct 2 05:55:00 EDT 2015

On Wed, Sep 30, 2015 at 11:22:10PM -0400, ianG wrote:
> Thought experiment.
> The blockchain [0] provides a way to do verifiable computing [1].
> Popularly under the tag of "smart contracts" these little scripts
> can be executed on every node, and the ability of the nodes to come
> together and find consensus on the state or results provides a way
> to not only compute, but also know that we have verifiably computed.
> Verifiable computing was a long treasured goal - but proved elusive
> outside an academically restricted set of assumptions.
> If we have verifiable computing finally in the blockchain - a thesis
> - does this mean we now have a trustworthy computing platform?

I really strongly disagree about the direction of what you're talking

I'd define trustworthy computing as being able to trust that a
computation was done correctly without you checking it yourself. This
implies that SPV clients are taking advantage of trustworthy computing
because they trust miners; full nodes are not doing that because they
verify the blockchain themselves.

In the Bitcoin world I think it's fair to say that most experts are very
concerned about the high, and increasing, % of users who use SPV clients
rather than run full nodes. While it's hard to predict exactly when this
threshold is reached, at some point too few people will be actually
verifying the blockchain to sufficiently strongly incentivise miners to
follow the rules. For instance, at some point miners can great bitcoins
out of thin air to increase their profits.

Instead there has been work done on going the other direction: using
better math to make verifying the blockchain cheaper and more practical.
But again, this isn't an example of trustworthy computing! It's standard
trustless computing, made more efficient by clever math.

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