[bitcoin-dev] Original Vision

Mark Friedenbach mark at friedenbach.org
Sun Jun 28 15:23:49 UTC 2015


There's a couple of things that Patrick could have been referring to when
he said "Fraud proofs need to be at least more efficient than full node
validation. Currently they are not."

One of the issues is that you cannot efficiently encode or validate a proof
of a negative. If a transaction input is a double-spend, you can build a
semi-reasonable sized proof of the prior spend (or very reasonably sized
with block header commitments). However if a transaction spends an output
which never existed in the first place, there is no reasonable way to
assert this other than witnessing the entire block history, as a full node
does.

UTXO commitments are the nominal solution here. You commit the validator
state in each block, and then you can prove things like a negative by
referencing that state commitment. The trouble is this requires maintaining
a hash tree commitment over validator state, which turns out to be insanely
expensive. With the UTXO commitment scheme (the others are not better) that
ends up requiring 15 - 22x more I/O during block validation. And I/O is
presently a limiter to block validation speed. So if you thought 8MB was
what bitcoin today could handle, and you also want this commitment scheme
for fraud proofs, then you should be arguing for a block size limit
decrease (to 500kB), not increase.

On Sat, Jun 27, 2015 at 10:32 PM, Eric Lombrozo <elombrozo at gmail.com> wrote:

> Just to clarify, SPV is fundamentally busted as it currently exists. I’m
> talking about potential optimizations for future protocols.
>
> - Eric Lombrozo
>
> > On Jun 27, 2015, at 10:29 PM, Patrick Strateman <
> patrick.strateman at gmail.com> wrote:
> >
> > Fraud proofs need to be at least more efficient than full node
> validation.
> >
> > Currently they are not.
> >
> > On 06/27/2015 09:54 PM, Eric Lombrozo wrote:
> >> Fraud proofs actually don’t need to be made super efficient…but they do
> need to be secure, of course.
> >>
> >> The trick is aligning incentives. In order for fraud proofs to be
> widely available there needs to be a market for them - there must be a way
> to buy one (because producing one is not free). What makes such a scheme
> actually practical is that very few of these fraud proofs ever need to
> actually be executed - it’s a classical Nimzowischian case of the threat
> being much stronger than the execution.
> >>
> >> - Eric Lombrozo
> >>
> >>> On Jun 27, 2015, at 7:13 PM, Patrick Strateman <
> patrick.strateman at gmail.com> wrote:
> >>>
> >>>> Further, it appears clear that the original author intended
> >>> organizations operating full network nodes would provide connectivity
> to
> >>> light clients and these light clients would make up the majority of the
> >>> user base.
> >>>
> >>> Satoshi also believed that fraud proofs would be widely available and
> >>> practical.
> >>>
> >>> If fraud proofs were practical SPV client security would be much closer
> >>> to full node security than it is today.
> >>>
> >>> Unfortunately no design for fraud proofs which is both efficient and
> >>> secure has been proposed; much less implemented and deployed.
> >>>
> >>> In building a system as new and innovative as bitcoin certain things
> >>> will be wrong.
> >>>
> >>> The perception that SPV clients could be made nearly as secure as full
> >>> nodes is one example of something that was wrong.
> >>>
> >>> On 06/27/2015 05:14 PM, Santino Napolitano wrote:
> >>>> There is much heated debate going on right now and I know it can be
> very stressful but I'd like to point out that it is really amazing how
> passionately so many feel about this once very small project. Let's not
> forget there is something really special going on here and we're all part
> of it.
> >>>>
> >>>> The current debate has little to do with block size or hard-forks,
> IMO. It's about the nature of Bitcoin and what it means to people and how
> it will grow. I would like to take a moment to share my interpretation of
> the original author's intent based on everything I could find and read from
> this person. This is not to say their original vision is paramount-- or
> even that I got it completely correct but I think it might do us some good
> to think about.
> >>>>
> >>>> It seems as though the incentive conceived of for running a full
> network node was that it would enable mining. The proceeds from mining (new
> coins and transaction fees) would be the reward and provide a reason to
> continue operating these nodes. If fees are ever to be a sufficient reward
> and still allow for a practical and useful system the size of the blocks
> must grow significantly as must the user base. I'm not sure that this is
> really contested but I haven't exhaustively reviewed everyone's opinion so
> please excuse me if I have marginalized you. If you do contest that I would
> be interested in hearing it.
> >>>>
> >>>> Further, it appears clear that the original author intended
> organizations operating full network nodes would provide connectivity to
> light clients and these light clients would make up the majority of the
> user base. This is completely consistent with current trends in Internet
> consumption, e.g. tablets and phones are becoming more preferred to even
> owning a traditional computer. Having the system be entirely decentralized
> and trustless for every client does not appear to me to be the original
> design goal. Yes, the whitepaper speaks of the design goal as not having a
> need for a trusted third party but it does not say that some amount of
> trust won't be preferred by a majority of users. In fact, in the SPV
> section it implies some amount of localized trust is perhaps a necessary
> trade-off and maybe businesses should still run their own full network node
> if they want the stronger completely trustless guarantee. The global
> decentralized consensus appears meant to make the network
> >>> r
> >>>> esilient to a single government or other adversary's ability to shut
> the network down. If you really want to trust no one it is your option at a
> cost and should be possible by design. The author further gives evidence
> that they believe Moore's observation would keep the idea of running a full
> network node a practical one at global scale for perpetuity. It does not
> appear as if they intended for every individual to run one at home nor in
> their pocket.
> >>>>
> >>>> If my interpretation seems incorrect please do point it out. I hope
> this hasn't been too off-topic and distracting. The original author's
> engineering ingenuity is what gave me any interest in this project so
> re-visiting their design and scaling intentions might be helpful for us to
> move forward-- together.
> >>>>
> >>>> _______________________________________________
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> >>>
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