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

From: Matt Corallo <[email-masked]>
Date: Mon, 9 Jun 2025 09:51:56 -0400

First of all, lol, we're really doing sign-on letters again? Great way to discourage people from 
doing things.

That said, I have yet to see a reasoned explanation of why we should prefer CTV over TXHASH. Any 
time I bring it up I get a few handwave arguments about "that would require bikeshedding", but I 
don't see why that is an argument. Preferring to do something worse because something better would 
require someone reasonable pick some reasonable encoding is not a good way to do engineering.

Maybe one of the letter-signers wants to provide an explanation for their view?

Matt

On 6/9/25 7:40 AM, 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)
> Seth for Privacy (for Cake Wallet)
> Simanta Gautam (Alpen Labs)
> Steven Roose (@stevenroose)
> stutxo (@stutxo)
> Talip (@otaliptus)
> mononaut (@mononautical)
> vnprc (@vnprc)
> 
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