[bitcoin-dev] Standard BIP Draft: Turing Pseudo-Completeness

Jorge Timón jtimon at jtimon.cc
Sat Dec 12 20:00:43 UTC 2015


On Fri, Dec 11, 2015 at 10:45 PM, Luke Durback <luke.durback at gmail.com> wrote:
>>If it's voting for something consensus, you will need something special. If
>> it's not consensus (ie external) thw voting doesn't have to hit the chain at
>> all.
>
> I had in mind voting for something that can't be trusted if done externally:
> Perhaps BIPs for instance.  People would somehow "mark" their BTC as being
> "For Proposition X" (as opposed to all other propositions) and the vote
> would be canceled as soon as the BTC is spent again.
>
> Unfortunately, I've spent the past 2 days trying to find a design that would
> allow this (I don't think my original suggestion made sense in the context
> of how transactions work), and I haven't gotten much yet.

Well, as said, if it's for consensus, you will need to adapt the
system in a special way anyway, but I still don't see why turing
completeness is required.
This type of idea is not new. Since miners can censor votes (and
that's undetectable for consensus), several solutions have been
proposed, time lock the votes, for example.

>>But each scriptSig is only executed once with its corresponding
>> scriptPubKey. Are you proposing we change that?
>
> Sorry, I didn't understand Bitcoin's transaction model well enough when I
> first made the proposal.  If Turing Pseudo-Completeness is possible with
> Bitcoin, then I understand now that it could not require you to execute a
> script more than once.  My current thought is that recursion can be
> accomplished via checking if the next output's scriptPubKey is identical in
> every way to the current scriptPubKey.  Unfortunately, a lot more is needed
> than just recursion in order to do on-chain BTC voting the way I have in
> mind.  I'll keep working on this.

What you call "recursion" seems similar to what we usually call "covenants", see

https://bitcointalk.org/index.php?topic=278122.0

Although the thread says "an amusingly bad idea", I think it's
actually a great idea and there's some use cases that are very hard to
support without covenants.
Again, no Turing completeness required for this.

> On Fri, Dec 11, 2015 at 10:36 AM, Jorge Timón <jtimon at jtimon.cc> wrote:
>>
>>
>> On Dec 10, 2015 7:36 AM, "Luke Durback" <luke.durback at gmail.com> wrote:
>> >
>> > Tomorrow, I'll work on writing a way to do voting on proposals with BTC
>> > used as voting shares (This will be difficult as I do not know FORTH).  That
>> > seems like a fairly simple, useful example that will require loops and
>> > reused functions.  I'll add a fee that goes to the creator.
>>
>> If it's voting for something consensus, you will need something special.
>> If it's not consensus (ie external) thw voting doesn't have to hit the chain
>> at all.
>> I don't see how "loops and reused functions" are needed in the scripting
>> language for this use case, but I'm probably missing some details. Please,
>> the more concrete you make your example, the easiest it will be for me to
>> understand.
>>
>> > IMO, if you write a complicated system of scripts that's used
>> > frequently, it makes sense to charge a fee for its usage.
>>
>> But each scriptSig is only executed once with its corresponding
>> scriptPubKey. Are you proposing we change that?
>>
>> >  A decentralized exchange between colored coins, for instance might take
>> > a small fee on each trade.
>>
>> I've been researching the topic of decentralized exchange from before the
>> term "colored coins" was first used (now there's multiple designs and
>> implementations); contributed to and reviewed many designs: none of them
>> (colored coins or not) required turing completeness.
>> I'm sorry, but what you are saying here is too vague for me to concretely
>> be able to refute the low level "needs" you claim your use cases to have.
>>
>> > On Dec 10, 2015 10:10 AM, "Luke Durback via bitcoin-dev"
>> > <bitcoin-dev at lists.linuxfoundation.org> wrote:
>> > > This, combined with the ability to make new transactions arbitrarily
>> > > would allow a function to pay its creator.
>> >
>> > I don't understand what you mean by "a function" in this context, I
>> > assume you mean a scriptSig, but then "paying its creator" doesn't make much
>> > sense to me .
>> >
>> > Could you provide some high level examples of the use cases you would
>> > like to support with this?
>
>


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