Subject: Re: [bitcoindev] CTV + CSFS: a letter

From: "'Antoine Poinsot' via Bitcoin Development Mailing List" <[email-masked]>
Date: Tue, 17 Jun 2025 14:34:35 +0000

Steven,

> I'd like to first express my disappointment with the amount of drama this letter has caused.

Likewise. As i mentioned earlier i think this bundle of capabilities is worth considering for a use case driven soft fork. I felt like, despite the lack of substantive work on the proposal, we were finally going somewhere in the discussion on extending Bitcoin's scripting capabilities.

Instead of addressing minor objections to the design of the operations and working on demonstrating (real) use cases, the champion chose the route of political pressure on the Bitcoin Core project. Signatories backed this approach.

In changing Bitcoin, the process matters as much as the outcome. If Bitcoin can be changed through a shouting match and on the basis of misleading pseudo use cases, it would be a major fuck up. Likewise if a suboptimal change can be rammed through without addressing objections and reasonable requests from the technical community, by bamboozling industry stakeholders into the false dichotomy "it's either this or ossification".

Bitcoin Core cannot, in my opinion, facilitate setting such a precedent. Therefore this effort sets us back a long way in getting a consensus change merged there, and on the broader path of extending Bitcoin's scripting functionalities

> It quite literally merely asks Core contributors to put this proposal on their agenda with some urgency.

This is incorrect and misrepresenting the content of the letter. It specifically asks, i'm quoting "integration of CTV (PR [#31989](https://github.com/bitcoin/bitcoin/pull/31989) or similar)". This is asking Core to merge a pull request implementing a contentious consensus change. And so, not by making the case for it with strong technical arguments but by presenting signatures from industry stakeholders. I trust we all both agree it is inadvisable to change the Bitcoin Core decision process from making software changes based on objective rough technical consensus toward making software changes based on the subjective intentions of whoever has influence in the space at the moment.

> Given that only a handful of Core contributors had thus far participated in the conversation on the proposal elsewhere

And pressure to merge code for an obviously controversial consensus change is a great way to make sure not more of them engage, if lurking at how [previous CTV discussions went](https://delvingbitcoin.org/t/ctv-csfs-can-we-reach-consensus-on-a-first-step-towards-covenants/1509/37?u=antoinep) wasn't enough.

> it seemed like a suitable next step to communicate that we want Core contributors to provide their position within this conversation

How could you ever think it be a "suitable next step"? Bitcoin Core contributors spend their days maintaining the existing Bitcoin network, where making it boringly stable is success. Asking the project to merge a contentious consensus change, disregarding conceptual review, is just laughable. I don't see how piling a sign-on letter on top of this would improve anything.

In conclusion, i would like to state i understand the frustration of this proposal not making progress and how it led many signatories to get on board with the letter. I do not ascribe bad intentions to most of them. However the effect of this letter has been, as could have been expected, a major setback in making progress on this proposal (or more broadly this bundle of capabilities). I am not sure how we bounce back from this, but it necessarily involves someone standing up and actually doing the work of addressing technical feedback from the community and demonstrating (real) use cases. The way forward must be by building consensus on the basis of strong objective, technical, arguments. Not with a bunch of people stating interest and nobody acting up and helping the proposal move forward.

Best,
Antoine Poinsot
On Tuesday, June 17th, 2025 at 7:31 AM, Steven Roose <[email-masked]> wrote:

> Hey all
>
> I've been following the discussion and noticed TXHASH is mentioned a lot. As a signer of the letter and author of the TXHASH proposal, I'd like to chime in with some thoughts.
>
> However, I'd like to first express my disappointment with the amount of drama this letter has caused. It quite literally merely asks Core contributors to put this proposal on their agenda with some urgency. No threats, no hard words.
> Given that only a handful of Core contributors had thus far participated in the conversation on the proposal elsewhere, it seemed like a suitable next step to communicate that we want Core contributors to provide their position within this conversation.
> I strongly stand against an approach involving independent activation clients and I think the sentiment of this e-mail aligns with the preference of having Core be involved in any deployment of protocol upgrades.
>
> On the proposal itself. I have heard some mentions of TXHASH and why we, as the developer community, wouldn't go straight for TXHASH.
>
> - I think TXHASH is too far from being ready at this point:
>
> - The TXHASH BIP and spec has not had the level of review/engagement that I had hoped for. I'm personally pretty happy with the result, especially since it only has had serious looks from myself and Rearden. But it definitely needs a lot more scrutiny. It's a very opinionated design (I think it's unavoidable for such an opcode), so there is a lot of room for making different and maybe better decisions on many fronts.
> - Once we have the TXHASH semantics, it would be very valuable to consider also introducing the same semantics as a top-level sighash flag system, so you can spend coins directly with a sighash based on TXHASH semantics. (I dubbed this TXSIGHASH and I recently did some simulations on how such a construction would look for fee sponsoring and stacking https://delvingbitcoin.org/t/jit-fees-with-txhash-comparing-options-for-sponsorring-and-stacking/1760)
> - However, this also invites some additional review of possible taproot changes (pay-to-tapscript, re-adding parity byte, ..) and will necessarily take some more time for consideration and design.
> - I strongly believe it would benefit development of new bitcoin use cases if we would have a simple version of templating and rebindable signatures sooner rather than later. Both BitVM and Ark are fairly recent ideas that stand to benefit significantly from such new functionality, but I think having them actually available will invite a lot more engagement leading to new ideas and new improvements. These are not use case-specific changes, but useful general building blocks.
> - Both CSFS and CTV are fairly unopinionated opcodes by design, when you think of CTV in the sense that it fixes the minimum tx fields to ensure txid stability.
> - I think there is both enough excitement for this proposal and there would be enough future excitement for a TXHASH or CCV addition that I don't fear upgrade churn will be a future hurdle.
> - Even after possible TXHASH activation, I think there will stay some demand for the simpler CTV/TEMPLATEHASH variant. It doesn't just save a byte on the wire, but thinking in a txid-stable model is just more intuitive. I believe that many advanced use cases will take advantage from doing things the TXHASH way (enabling stacking and cheaper fee sponsoring), but some developers will always favor the simplicity of txid stability over the benefits of adding complexity.
>
> The above arguments convinced me that an activation based on CTV and CSFS makes sense today. We have lots of developers waiting to make use of the functionality it enables and we can continue development of further changes meanwhile.
>
> That being said, I'm in no way married to the exact details of the proposals.
>
> - I am sympathetic to worries of changing legacy/v0 script. I failed to convince myself of any valuable usage for bare CTV.
> - I am sympathetic to the consideration of revisiting scriptSig and annex-related modifications to the template hash.
> - I am sympathetic to the decision to optimize better for the rebindable signature use cases, meaning:
>
> - the idea to swap CTV for a TEMPLATEHASH opcode which adds a 1-byte VERIFY for the template use case but saves 33 bytes for the signature use case
> - the addition of an INTERNALKEY opcode, saving an additional 33 bytes for the rebindable signature use case
> All of the above changes I think can be decided on with minimal bikeshedding and still encompass the same semantics of the original proposal.
>
> Best
>
> Steven
>
> On 6/9/25 12:40, James O'Beirne wrote:
>
>> Good morning,
>>
>> A letter has been published advocating for the final review and
>> activation of OP_CHECKTEMPLATEVERIFY (BIP-119) and OP_CHECKSIGFROMSTACK
>> (BIP-348).
>>
>> The full text of the letter can be found at https://ctv-csfs.com. It is
>> reproduced below.
>>
>> ---
>>
>> To the technical bitcoin community,
>>
>> We believe that the best next step for bitcoin would be to activate
>> OP_CHECKTEMPLATEVERIFY (CTV, BIP-119) and OP_CHECKSIGFROMSTACK (CSFS,
>> BIP-348). These opcodes enable functionality for a broad set of uses
>> that will allow bitcoin to preserve and expand its role as a scarce,
>> censorship-resistant store of value.
>>
>> While there are a few promising proposals to improve bitcoin at the
>> consensus layer which may someday be deployed, we believe that CTV and
>> CSFS are uniquely well reviewed, simple, and have been proven to be both
>> safe and widely demanded.
>>
>> CTV was first formalized in BIP-119 over 5 years ago. Despite many
>> attempts at refinement or replacement, it has remained the most widely
>> preferred method for enforcing pregenerated transaction sequences using
>> consensus. It unlocks valuable functionality for scaling solutions,
>> vaults, congestion control, non-custodial mining, discreet log
>> contracts, and more.
>>
>> CSFS is a primitive opcode that has been deployed to Blockstream’s
>> Elements for at least 8 years. It represents no significant
>> computational burden over bitcoin’s most often used opcode, OP_CHECKSIG.
>> It can be combined with CTV to implement ln-symmetry, a longstanding
>> improvement to Lightning. It also unlocks a variety of other use cases.
>>
>> We respectfully ask Bitcoin Core contributors to prioritize the review
>> and integration of CTV (PR #31989 or similar) and CSFS (PR #32247 or
>> similar) within the next six months. We believe this timeline allows for
>> rigorous final review and activation planning.
>>
>> This request isn't meant to suggest that these contributors dictate the
>> consensus process, but rather it is an acknowledgement that before these
>> opcodes can be activated, they must be implemented in the most widely
>> used bitcoin client.
>>
>> As application and protocol developers, we are convinced of the
>> significant benefits that these changes would bring to end users of
>> bitcoin – even if only considering their use for layer 1 security and
>> layer 2 scaling solutions. We are optimistic that given the limited size
>> and scope of these changes in both concept and implementation, they
>> represent a realistic next step in the continuing and important work of
>> preserving bitcoin's unique promise.
>>
>> Signed,
>>
>> Abdel (Starkware)
>> Andrew Poelstra (@apoelstra)
>> Ben Carman (@benthecarman)
>> Ben Kaufman (@ben-kaufman)
>> Brandon Black (@reardencode)
>> Brian Langel (for Five Bells)
>> Buck Perley (@puckberley)
>> Calle (Cashu)
>> Calvin Kim (@kcalvinalvin)
>> Chun Wang (f2pool)
>> Christian Decker (@cdecker)
>> Coinjoined Chris (Bitsurance.eu)
>> Evan Kaloudis (for Zeus)
>> fiatjaf (@fiatjaf)
>> Floppy (@1440000bytes)
>> Gary Krause (@average-gary)
>> Harsha Goli (@arshbot)
>> Hunter Beast (@cryptoquick)
>> Jad Mubaslat (@champbronc2)
>> James O’Beirne (@jamesob)
>> Jameson Lopp (@jlopp)
>> Johan Halseth (@halseth)
>> Luke Childs (@lukechilds)
>> Matt Black (for Atomic Finance)
>> Michael Tidwell (@miketwenty1)
>> Nick Hansen (for Luxor Mining)
>> Nitesh (@nitesh_btc)
>> nvk (@nvk)
>> Owen Kemeys (for Foundation)
>> Paul Sztorc (@psztorc)
>> Portland.HODL (for MARA Pool)
>> Rijndael (@rot13maxi)
>> Rob Hamilton (@rob1ham)
>> Robin Linus (@RobinLinus)
>> Sanket Kanjalkar (@sanket1729)
>> Sean Ryan (Anchorage)
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>> Simanta Gautam (Alpen Labs)
>> Steven Roose (@stevenroose)
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>>
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