Subject: Re: [bitcoindev] What's a good stopping point? Making the case for the capabilities enabled by CTV+CSFS

From: "'Antoine Poinsot' via Bitcoin Development Mailing List" <[email-masked]>
Date: Fri, 04 Jul 2025 13:02:54 +0000

I agree the BitVM/CTV idea suggests inspection of other inputs can be useful for applications
leveraging connector outputs.

While it is potentially compelling, the BitVM use case was only briefly presented, with no
demonstration or even detailed description of how it would work in practice. This makes it hard to
assess the costs and benefits of this approach. Furthermore, it's hard to assess how much of an
improvement it brings to Bitcoin users as BitVM has yet to be delivered and see any meaningful
adoption.

As Greg responded when it was raised earlier in this thread[^0], as things stand today i don't think
this idea justifies the leap in expressivity.

Best,
Antoine

[^0]: https://gnusha.org/pi/bitcoindev/[email-masked]

On Thursday, July 3rd, 2025 at 4:54 AM, Anthony Towns <[email-masked]> wrote:

> 
> 
> On Tue, Jun 24, 2025 at 11:54:02AM -0400, Matt Corallo wrote:
> 
> > > which
> > > warrants a compelling demonstration that arbitrary transaction introspection
> > > does enable important use cases not achievable with more minimal capabilities.
> > > I'm somewhat skeptical that showing this isn't rather simple,
> 
> 
> I think the BitVM/CTV idea posted on delving [0] is one such simple demo?
> 
> I gave an example in that thread of how you'd implement the desired
> construct using bllsh's introspection primitives, but the same could
> equally well be done with Rusty's as-yet unpublished OP_TX, something
> like:
> 
> DUP 0x1011 TX 0x00000002 EQUALVERIFY 0x1009 TX 0x0809 TX EQUALVERIFY
> 
> where:
> 
> * "0x1011 TX" pops an input index from the stack and gives the four-byte
> vout index of that input's prevout
> * "0x1009 TX" pops an input index from the stack and gives the txid of that input's
> prevout
> * "0x0809 TX" gives the txid of the current input's prevout
> 
> (this encodes "this utxo can only be spent (via this path) if its sibling
> output at index 2 is also being spent in the same transaction")
> 
> Cheers,
> aj
> 
> [0] https://delvingbitcoin.org/t/how-ctv-csfs-improves-bitvm-bridges/1591
> 
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