Subject: Re: [bitcoin-dev] Automatically reverting ("transitory") soft forks, e.g. for CTV

From: Matt Corallo <[email-masked]>
Date: Thu, 21 Apr 2022 16:02:26 -0700

On 4/21/22 3:28 PM, David A. Harding wrote:
> On 21.04.2022 08:39, Matt Corallo wrote:
>> We add things to Bitcoin because (a) there's some demonstrated
>> use-cases and intent to use the change (which I think we definitely
>> have for covenants, but which only barely, if at all, suggests
>> favoring one covenant design over any other)
> 
> I'm unconvinced about CTV's use cases but others have made reasonable claims that it will be used.  
> We could argue about this indefinitely, but I would love to give CTV proponents an opportunity to 
> prove that a significant number of people would use it.

To be clear - I was not suggesting that CTV fell flat here. I think there *is* demand for Bitcoin 
covenant designs, CTV included. I do *not* think there is demand for CTV *over* other covenant 
designs, that's okay, though, it doesn't need that, we just have to be confident its the right 
direction.

I believe you got the impression I was arguing CTV did not meet by criteria list (a)-(d), but in 
fact I only think it falls flat horribly on (c).

>> (b) because its
>> generally considered aligned with Bitcoin's design and goals, based on
>> developer and more broad community response
> 
> I think CTV fulfills this criteria.  At least, I can't think of any way BIP119 itself 
> (notwithstanding activation concerns) violates Bitcoin's designs and goals.

I tend to agree.

>> (c) because the
>> technical folks who have/are wiling to spend time working on the
>> specific design space think the concrete proposal is the best design
>> we have
> 
> This is the criteria that most concerns me.  What if there is no universal best?  For example, I 
> mentioned in my previous email that I'm a partisan of OP_CAT+OP_CSFS due to their min-max of 
> implementation simplicity versus production flexibility.  But one problem is that spends using them 
> would need to contain a lot of witness data.  In my mind, they're the best for experimentation and 
> for proving the existence of demand for more optimized constructions.

I agree, there is no universal best, probably. But is there a concrete listing of a number of 
use-cases and the different weights of things, plus flexibility especially around forward-looking 
designs? You don't mention the lack of recursion in CTV vs CAT+CSFS, which is a *huge* difference in 
the available design space for developers. This stuff is critical to get right and we're barely even 
talking about it, let alone at a position of deciding something?

>> I do not see how we can make an argument for any specific covenant
>> under (c) here. We could just as well be talking about
>> TLUV/CAT+CHECKSIGFROMSTACK/etc, and nearly anyone who is going to use
>> CTV can probably just as easily use those instead - ie this has
>> nothing to do with "will people use it".
> 
> I'm curious how we as a technical community will be able to determine which is the best approach.  
> Again, I like starting simple and general, gathering real usage data, and then optimizing for 
> demonstrated needs. But the simplest and most general approaches seem to be too general for some 
> people (because they enable recursive covenants), seemingly forcing us into looking only at 
> application-optimized designs.  In that case, I think the main thing we want to know about these 
> narrow proposals for new applications is whether the applications and the proposed consensus changes 
> will actually receive significant use.  For that, I think we need some sort of test bed with real 
> paying users, and ideally one that is as similar to Bitcoin mainnet as possible.

Again, you're writing off the real and nontrivial risk of doing a fork to begin with. You're also 
writing off something organic that has happened without issue time and time again - a community of 
independent contributors who care about Bitcoin working together to make decisions on what is or 
isn't the "right way to go" is something we've all collaboratively done time and time again. Why are 
you suggesting its something that you "don't know how to do"?

Again, my point *is not* "will people use CTV", I think they will. I think they would also use TLUV 
if that were activated for the exact same use-cases. I think they would also use CAT+CSFS if that 
were what was activated, again for the exact same use-cases. Given that, I'm not sure how your 
proposal teaches us anything at all, aside from "yes, there was demand for *some* kind of covenant".

Matt