path: root/57/d256c27ace406960f7b3a4bf62caa38ae3638e

Delivery-date: Wed, 25 Jun 2025 14:28:09 -0700
Received: from mail-oo1-f64.google.com ([209.85.161.64])
	by mail.fairlystable.org with esmtps  (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
	(Exim 4.94.2)
	(envelope-from <bitcoindev+bncBDSJ7DXSQ4PRBX6T6HBAMGQERJ2TH5Y@googlegroups.com>)
	id 1uUXf6-0005SX-MK
	for bitcoindev@gnusha.org; Wed, 25 Jun 2025 14:28:09 -0700
Received: by mail-oo1-f64.google.com with SMTP id 006d021491bc7-611a459c886sf463326eaf.1
        for <bitcoindev@gnusha.org>; Wed, 25 Jun 2025 14:28:08 -0700 (PDT)
ARC-Seal: i=2; a=rsa-sha256; t=1750886882; cv=pass;
        d=google.com; s=arc-20240605;
        b=dV84GH4ZWpx1AhjbvPSY5zx/WGXbB8qkRBAC0mQyZRrAIsDdQm2j9TWhDuFM8IogAF
         GJMngzkioKE5yFVESEmyAPjnrpmox6y91LKWQatRzmjIN54g7yID+2M9lQV+kaSouz26
         Ju8PfZu2l6dwGrdz1DmOgiVW3LS/5CsAtk+LYsSyv34NtEsLt7hEumv+kHz+QryRvmPi
         MNUvH7d9mGcyMu1ABuPMnkM4l54Yqf5RoGozVZX+aGbWHyDQdDlj6HAyFKXHvOB7ZneL
         K/5YoBCYRNazcbrH7UUxn5ZUHgrafFOfMWrjNA6veMzeMUeuXM397UWexqMow+c0Fxp1
         IKEw==
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605;
        h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post
         :list-id:mailing-list:precedence:content-transfer-encoding:cc:to
         :subject:message-id:date:from:in-reply-to:references:mime-version
         :sender:dkim-signature:dkim-signature;
        bh=kr6N1mgI4NoCHQgihJOI7/AWxQyjBBUh8EiyDMDYPx0=;
        fh=FO6ukmeJ02Q33JC/6tDXaHZxLhVQPE03/CCIab0pklY=;
        b=DmyBu1yHlwwiXMwmJ0Im16hd0rAwfEPf6cQTfhk5klgqktbpeMFRps0Y3OZoqwcFON
         6Aq8MfgN8ZU8G+2UFPuYvAR0yTWXPnwATQ+i8ZkfGXJF8CTr+KifgFCNg+VqGzPSxJ29
         egwHq0L10E5T/zxGIF4PeNRlXdVRN1cBWsnSl/fb0mjBZKdUUPl3BMbFHr7XCnHIdew2
         9/xYPOErZB99HkY/WfNzx8CF+jKSUEmqWm+zkSqrJrqdy6y06soK3BZNsit2ySmpBpGw
         MWlxWHTNl7C6wkCPEitRGv12PFTil+YBfjYrXjk7eXygL/TbEtDJGt0aWbHe7W9DFp22
         phaQ==;
        darn=gnusha.org
ARC-Authentication-Results: i=2; gmr-mx.google.com;
       dkim=pass header.i=@gmail.com header.s=20230601 header.b=Vy7oAxZz;
       spf=pass (google.com: domain of eth3rs@gmail.com designates 2a00:1450:4864:20::531 as permitted sender) smtp.mailfrom=eth3rs@gmail.com;
       dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com;
       dara=pass header.i=@googlegroups.com
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=googlegroups.com; s=20230601; t=1750886882; x=1751491682; darn=gnusha.org;
        h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post
         :list-id:mailing-list:precedence:x-original-authentication-results
         :x-original-sender:content-transfer-encoding:cc:to:subject
         :message-id:date:from:in-reply-to:references:mime-version:sender
         :from:to:cc:subject:date:message-id:reply-to;
        bh=kr6N1mgI4NoCHQgihJOI7/AWxQyjBBUh8EiyDMDYPx0=;
        b=BEn4gaJd3FcFQUj7vmN1imgiKa9C/oXnizMUNEflCO+PqwvgjtR3RmYnufo+n6fTN9
         rdLNFyONFTeh/vbmtdQ6m71xfMtq/cMrzInacQ+dV1IdlCjNXUot3FsNGgbRT2HJu33j
         kpOL3wAjTYJ422CA4DuSmEej7L08juaA3WBQkw78/IH5NMqcA1PblDHuTUaiES1SWGFG
         95E6u8lOVY7lUTbYu3oCWZ2DlpJY0U4PyySDIcRc7EMcjm/aaHspy+Y9FrY7ZlMsHBtS
         Rt3qJBB+yazw0Pf8NfZRV5suBohNwwx/g5c0JppQVJGqXEaB6Zr16VXsXNobKL00MzVy
         a75g==
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20230601; t=1750886882; x=1751491682; darn=gnusha.org;
        h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post
         :list-id:mailing-list:precedence:x-original-authentication-results
         :x-original-sender:content-transfer-encoding:cc:to:subject
         :message-id:date:from:in-reply-to:references:mime-version:from:to:cc
         :subject:date:message-id:reply-to;
        bh=kr6N1mgI4NoCHQgihJOI7/AWxQyjBBUh8EiyDMDYPx0=;
        b=PHEqI7zlOt5n/5uVBAL66jwHsKlPXKGtQ1rty6sGfb+LsXKOkWHLtkhyo8Ra/msb/f
         S7I4iw6kDMthKykombzzKvuoVdnV1uZZb0wyCe+vyN868lLQZ8+zOaaGASyUJ5v5Rzhv
         servzB14qI8WLIKnmd6TLL7HlkfjsEimipQ2Ooy4Rdc7yqbf0UF9rutCDG+5gaMlbD9B
         0ILiKb7fY2s9mF0ELb3wPdsB2/N+E3OAJODVZ089vRBBpNG+InBIGNy7tx5vR1eI1EcW
         B0FbdODfItnpQTqkXjdL9O/8NysP0iDLCun1Eo80ep81eRHULCRRA0TtZ+inRodx4MTw
         iI7A==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=1e100.net; s=20230601; t=1750886882; x=1751491682;
        h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post
         :list-id:mailing-list:precedence:x-original-authentication-results
         :x-original-sender:content-transfer-encoding:cc:to:subject
         :message-id:date:from:in-reply-to:references:mime-version
         :x-beenthere:x-gm-message-state:sender:from:to:cc:subject:date
         :message-id:reply-to;
        bh=kr6N1mgI4NoCHQgihJOI7/AWxQyjBBUh8EiyDMDYPx0=;
        b=tcChY3ZdUdGpFW4uB4cywDDq5dtESGo6wKvPyC8hbQZt/zwkOUeFm3V+FksyagpqEy
         tgvrH/gcSAPXoVS9AbjOeTxUJmq1r9bkX90Rh0ilC1xTtlljWxaasP9DKhTaaTxF/yI9
         y5X0+Ob6c0dSFsogM2zl+jJNMq38EVwiUzo1z1+53I8p9vvEWXZYiAP6qEk83stIyXnt
         D/Fw9RXGCptYAnYwTLfufiwvPgf+V9g5I8x+hWFd20Tz0jwHq/TakaFBRt44Qbzb+Csb
         zOXeGd3dMmBpXIukQGtu/tyRdiGVz8Zc3oLjYXuwK+/g9LjOk1eSwaEi6xIanaUSL+Xp
         TcDQ==
Sender: bitcoindev@googlegroups.com
X-Forwarded-Encrypted: i=2; AJvYcCUKU37Zjdhciu/1g/pRjSz92yYJPpjFxw0E5JcOeQNemR4/Ro4AJCCHLEOsrIhQjLLJPABXnR6EZ/oa@gnusha.org
X-Gm-Message-State: AOJu0Yw3Act4C9WJUpGYeLmwfqkjJOC1TQBTLu9klk+Jha8/95UhiYgZ
	N5zG5rv7+Ph/DAWUNFH+giIragCXmh/OnQ8rf/8B5OrH0VetIU4IE4mY
X-Google-Smtp-Source: AGHT+IHiPpwcMavWq2qaOXRXad/Jrg2o35HsapuCNxaSwvGY/yyRvbiVa0jthfbFYKW1liPcHPZ3sg==
X-Received: by 2002:a05:6820:2905:b0:611:a1e4:59bf with SMTP id 006d021491bc7-611a1e45fe9mr2846423eaf.3.1750886882447;
        Wed, 25 Jun 2025 14:28:02 -0700 (PDT)
X-BeenThere: bitcoindev@googlegroups.com; h=AZMbMZfqNZq0arB2fONUqC/GYUhXLQGNkMi5oNy7gaESswvbcg==
Received: by 2002:a05:6820:6704:b0:611:7896:558b with SMTP id
 006d021491bc7-611ab00393fls305603eaf.0.-pod-prod-08-us; Wed, 25 Jun 2025
 14:27:59 -0700 (PDT)
X-Forwarded-Encrypted: i=2; AJvYcCXiBE6oT0ckOD0zHqzYoFHp2RDlJ0buAVqVKDMmmNa48/NyNVrDzioyN4qe+tblVuEr47YJ/0uOclMO@googlegroups.com
X-Received: by 2002:a05:6808:144e:b0:401:e721:8b48 with SMTP id 5614622812f47-40b05728f18mr3760012b6e.8.1750886879059;
        Wed, 25 Jun 2025 14:27:59 -0700 (PDT)
Received: by 2002:ab3:6f09:0:b0:2b1:9626:e73d with SMTP id a1c4a302cd1d6-2b5ec669d37msc7a;
        Wed, 25 Jun 2025 13:35:33 -0700 (PDT)
X-Forwarded-Encrypted: i=2; AJvYcCXbZ0cC0YVYCALlrcVbvqb6ohKj5eNXXSshPraoVujMDdQaF+YKbzpZRQsuGyK2T6cTztz3o3h85PUd@googlegroups.com
X-Received: by 2002:ac2:4c4e:0:b0:553:2375:c6e8 with SMTP id 2adb3069b0e04-55502c77bdbmr406682e87.1.1750883731394;
        Wed, 25 Jun 2025 13:35:31 -0700 (PDT)
ARC-Seal: i=1; a=rsa-sha256; t=1750883731; cv=none;
        d=google.com; s=arc-20240605;
        b=LJdVmjDf9A/OvOpR+Taahpn4s+DDSVcljYbYrMyNqyrjC4nR5f7cvs1LJ5BPgiLekl
         +zTl2qTcrXR7SgjtR6tI+AKwDcRCTzaEBc9k24WCkMcJ+baF/6If2MyZUKh/JH/sPqTp
         zMU/8DF+QyWfPh0AD8/ABEq0Tt67Tp+fW99vxmyP3s1t35a2M/vkZT+ZGqu8mp/SQE5P
         pKd7nADyds+HckPQLjqA+oSnjIPc4lLMbTTnbKR0j+r/jYc1u1wu8J1wwDbOWEINFIHP
         mR9NVqlyPfvbjfNtg1n3156NheP4z7jS5xktq7zWcHDqS4g3Q4bWwXUiI61vXI2xLSgz
         6PQw==
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605;
        h=content-transfer-encoding:cc:to:subject:message-id:date:from
         :in-reply-to:references:mime-version:dkim-signature;
        bh=hPskBSotwOlHWHNpBgE8Y+CNz/HZVlH5trSoWJxD21Q=;
        fh=Pr3bf1QCh5DOSMlJOC3ssp7X/Lygtlgys0mj6X7KCQI=;
        b=ZSKwxdyNr2hmGD/P5f8+XogVtCeQiVlQKO8Zu5dpiZetaC0Lfs7wIlJcgDnmsepRPT
         vXKVRExRNA9LOCpwWHYH9339mV2eiSVbeHPYtcOoU+yc+yZWS8tSQtXW1q6AegRD8lkM
         QaiG/1XHG6ErivjsoMmcf6L8B1Rb+h8CPO9tSymIpz+G/AJ5a+Fqt5TbNIv8jwl09DhB
         sv58Ln2f1Wn7DVdq5tU7yPD3TrQFtE7FHtbSxyXuo45bh0PSrHeHOZPuSlnK3MaYvaBJ
         fvgH5zjG51vuu1j51s52a/OzJLfMuX/n3rEppoGi4AhLho1r5OzEfAEbsfUutTPkufPA
         AqDA==;
        dara=google.com
ARC-Authentication-Results: i=1; gmr-mx.google.com;
       dkim=pass header.i=@gmail.com header.s=20230601 header.b=Vy7oAxZz;
       spf=pass (google.com: domain of eth3rs@gmail.com designates 2a00:1450:4864:20::531 as permitted sender) smtp.mailfrom=eth3rs@gmail.com;
       dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com;
       dara=pass header.i=@googlegroups.com
Received: from mail-ed1-x531.google.com (mail-ed1-x531.google.com. [2a00:1450:4864:20::531])
        by gmr-mx.google.com with ESMTPS id 2adb3069b0e04-553e41c0307si447808e87.8.2025.06.25.13.35.31
        for <bitcoindev@googlegroups.com>
        (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128);
        Wed, 25 Jun 2025 13:35:31 -0700 (PDT)
Received-SPF: pass (google.com: domain of eth3rs@gmail.com designates 2a00:1450:4864:20::531 as permitted sender) client-ip=2a00:1450:4864:20::531;
Received: by mail-ed1-x531.google.com with SMTP id 4fb4d7f45d1cf-60c01b983b6so720553a12.0
        for <bitcoindev@googlegroups.com>; Wed, 25 Jun 2025 13:35:31 -0700 (PDT)
X-Forwarded-Encrypted: i=1; AJvYcCWoH6Cp+/cQ1igSfOt7tl907SXnfGcZ+nijOLoJyVneRfl048IITluThYXxLOaz+jDdrl+5RAnlHDWn@googlegroups.com
X-Gm-Gg: ASbGncsdiuChTAj5MhjciOx6ilDrtGQFVOd9DG9+jKO4Qhz6HtEqnE+3bDZ04LqAdSY
	yiCEU1qVzZjN1cyuVtqtC2g3I8AayBed67+z8DBdmPG1gjfuIlzkoVqPcPllCKT0UeGaeMMn4LP
	4D19CLZ+b1MGhNjxVcdeXkixLrx7E0k6sBUwh3d3GG2O/uHF+hOonkVRToDycLc0crcdPRgLWM7
	bs+wA==
X-Received: by 2002:a05:6402:5242:b0:602:427c:452b with SMTP id
 4fb4d7f45d1cf-60c66f5b5cemr941263a12.3.1750883730373; Wed, 25 Jun 2025
 13:35:30 -0700 (PDT)
MIME-Version: 1.0
References: <F5vsDVNGXP_hmCvp4kFnptFLBCXOoRxWk9d05kSInq_kXj0ePqVAJGADkBFJxYIGkjk8Pw1gzBonTivH6WUUb4f6mwNCmJIwdXBMrjjQ0lI=@protonmail.com>
 <8a9a2299-ab4b-45a4-8b9d-95798e6bb62a@mattcorallo.com> <73PXNVcmgiN2Kba63P2SRZfs42lvgME_8EF-DlYtkOSY8mLRxEXPEw5JAi5wtPU2MEMw1C6_EDFHKKrhaa1F53OgIJOcam-kbOUP3aG2_e0=@protonmail.com>
In-Reply-To: <73PXNVcmgiN2Kba63P2SRZfs42lvgME_8EF-DlYtkOSY8mLRxEXPEw5JAi5wtPU2MEMw1C6_EDFHKKrhaa1F53OgIJOcam-kbOUP3aG2_e0=@protonmail.com>
From: Ethan Heilman <eth3rs@gmail.com>
Date: Wed, 25 Jun 2025 16:34:53 -0400
X-Gm-Features: Ac12FXxxn6VfXlXFkzxxobIGS7Cuoj6Nj9HUaKUl_C6a5fuQONLqyOxkcyfq33c
Message-ID: <CAEM=y+VGE1SbuApOx0Y0jnAYrd-eu_kWFbQf+EHEHyv7seeGGw@mail.gmail.com>
Subject: Re: [bitcoindev] What's a good stopping point? Making the case for
 the capabilities enabled by CTV+CSFS
To: Antoine Poinsot <darosior@protonmail.com>
Cc: Matt Corallo <lf-lists@mattcorallo.com>, 
	Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Original-Sender: eth3rs@gmail.com
X-Original-Authentication-Results: gmr-mx.google.com;       dkim=pass
 header.i=@gmail.com header.s=20230601 header.b=Vy7oAxZz;       spf=pass
 (google.com: domain of eth3rs@gmail.com designates 2a00:1450:4864:20::531 as
 permitted sender) smtp.mailfrom=eth3rs@gmail.com;       dmarc=pass (p=NONE
 sp=QUARANTINE dis=NONE) header.from=gmail.com;       dara=pass header.i=@googlegroups.com
Precedence: list
Mailing-list: list bitcoindev@googlegroups.com; contact bitcoindev+owners@googlegroups.com
List-ID: <bitcoindev.googlegroups.com>
X-Google-Group-Id: 786775582512
List-Post: <https://groups.google.com/group/bitcoindev/post>, <mailto:bitcoindev@googlegroups.com>
List-Help: <https://groups.google.com/support/>, <mailto:bitcoindev+help@googlegroups.com>
List-Archive: <https://groups.google.com/group/bitcoindev
List-Subscribe: <https://groups.google.com/group/bitcoindev/subscribe>, <mailto:bitcoindev+subscribe@googlegroups.com>
List-Unsubscribe: <mailto:googlegroups-manage+786775582512+unsubscribe@googlegroups.com>,
 <https://groups.google.com/group/bitcoindev/subscribe>
X-Spam-Score: -0.5 (/)

>  Why not even CAT, which is a neat tool in many situations and would let =
ZK people experiment with validation rollups? And at this point, it would s=
eem wiser to just work on a sane Bitcoin Script replacement rather than thr=
owing buckets of opcodes at it and hoping it holds off.

A Bitcoin Script replacement is likely to be a lot of work and many of
the features will be informed by what people are building at the time
it is designed. Merging a low implementation complexity opcode like
OP_CAT (BIP-347) would provide useful data to inform a Bitcoin Script
replacement.

In addition to allowing ZK people to experiment, OP_CAT also has many
simple use cases that improve everyday boring tapscripts.

> Sure, but I=E2=80=99d argue that the presence of risk now is a reason to =
be more cautious about adding to it, rather than accepting it as inevitable=
.

Addressing MEVil, if addressing MEVil is considered an important goal,
requires being proactive and enabling the ability to build better
protocols on Bitcoin. This is because, all things being equal,
building a protocol that doesn't care about MEVil resistance is easier
and requires less scripting functionality than one that does.

On Wed, Jun 25, 2025 at 12:54=E2=80=AFPM 'Antoine Poinsot' via Bitcoin
Development Mailing List <bitcoindev@googlegroups.com> wrote:
>
> Thanks for sharing some objections. Here is my attempt at addressing them=
.
>
> > ISTM even something as simple as a rate-limit requires more full-featur=
ed introspection than only
> > "commit to the exact next transaction" can provide. For example, a triv=
ial construction would be
> > something which requires that transactions spending an output have an o=
utput which claims at least
> > Amount - Rate, which requires both more full-featured introspection as =
well as a bit of math.
>
> Yes. These capabilities are really only useful for reducing interactivity=
 in second-layer protocols.
> They do not (reasonably) help for vaults and we do not claim it as a use =
case.
>
> Previous efforts to promote opcodes implementing those capabilities have =
unfortunately fallen into
> the trap of overpromising and claiming use cases they do not really enabl=
e. But this should not make
> us overlook what they are really good at: interactivity reduction.
>
> Do you think that the use cases presented in OP, if demonstrated, are not=
 enough to warrant soft
> forking in a primitive enabling them?
>
> > Given one of the loudest groups advocating for the additional features =
of CTV+CSFS are enterprise
> > or large-value personal custody providers
>
> Yes. We intentionally do not mention vaults as a use case in our steelman=
. We should not change
> Bitcoin on the basis of misleading use cases. If people are interested in=
 vaults, they should
> sponsor efforts on a different set of capabilities. Probably "programmabl=
e forwarding of value from
> inputs to outputs", "programmable forwarding of spending conditions from =
inputs to outputs" and maybe
> "commit to the exact transaction spending an output" (or more powerful in=
trospection).
>
> The lack of a similar enthusiasm for proposals enabling most or all of th=
ese functionalities (like
> Salvatore Ingala's BIP334 or previously James O'Beirne's and Greg Sanders=
' BIP345) suggests such
> loud support are in fact in favour of "just doing something" and rational=
ize nice-sounding use cases
> backward from this proposal (but vaults!) because it appears to them to b=
e "further down the road".
> I think this view is very dangerous and is part of our motivation for red=
irecting discussions toward
> what these capabilities actually enable.
>
> > it seems somewhat of a loss to not work our way towards really basic fe=
atures for this use-case.
>
> I personally grew more skeptical of the reactive security model of vaults=
 after working on it.  Your
> mileage may vary and that's fine if people want to work on capabilities t=
hat actually enable vaults,
> but i don't think they should be a required use cases and block introduci=
ng primitives that
> substantially improve existing layer 2s and make new ones possible.
>
> > Indeed, ISTM many use-cases for a construction like TXHASH become a lot=
 more substantial with Math
> > [...], I'm quite skeptical that *just* looking at an individual fork on=
 its own is the right
> > benchmark.
>
> I agree that modularity and forward composability with potential future u=
pgrades are arguments in
> favour of a more flexible approach. But those need to be balanced with th=
e additional risk and
> implementation complexity such an approach entails. I'm happy to be convi=
nced if supporters of this
> approach demonstrate the added flexibility does enable important use case=
s and the risks associated
> are manageable. But if nobody is interested in doing so, i don't think it=
's reasonable to hold off a
> safer upgrade as long as it is demonstrated to provide substantial benefi=
ts.
>
> It's also unclear that we should stop at "programmable introspection" in =
this case. Why not also
> include "programmable amount / spending condition forwarding" too, which =
would give you vaults? Why
> not even CAT, which is a neat tool in many situations and would let ZK pe=
ople experiment with
> validation rollups? And at this point, it would seem wiser to just work o=
n a sane Bitcoin Script
> replacement rather than throwing buckets of opcodes at it and hoping it h=
olds off. Which as we say
> in OP i don't think is realistic.
>
> > I don't see how this results in a net reduction in risk to Bitcoin, rat=
her just means more total
> > work and more cruft in Bitcoin's consensus.
>
> In theory, i agree. But by this token the same goes for every future exte=
nsion that introduces more
> expressivity to Bitcoin Script. This ties back to the stopping point: why=
 add more cruft to the
> existing interpreter when we could all focus on BTCLisp instead?
>
> It's also the case that even if future extensions introduce a superset of=
 the capabilities being
> discussed, it's unlikely that such simple ones like "just commit to the n=
ext transaction" and
> "verify a signature for an arbitrary message" would ever be made fully re=
dundant.
>
> Finally, when considering technical debt we should also weigh the actual =
cost of the implementation
> of these simple capabilities. Signature verification on arbitrary message=
 reuses existing signature
> checking logic. Similarly, committing to the next transaction can heavily=
 lean on existing Taproot
> signature messages, only minimally departing when necessary, and be imple=
mented in a strictly
> simpler manner than the existing CTV proposal. A minimal implementation o=
f these capabilities would
> not introduce significant technical debt.
>
> Interestingly, this argument applies more to introducing more involved ca=
pabilities like arbitrary
> transaction introspection, because of the substantially larger technical =
debt it would impose to
> first support in Bitcoin Script instead of focusing on a replacement with=
 transaction introspection
> from the get go.
>
> > Indeed, more flexible introspection provides for a difference in risk t=
o the system (though its
> > worth noting we cannot both argue that there is no "demonstrated utilit=
y" *and* that the utility
> > of a change is so substantially higher that it adds material risk to th=
e system in the form of
> > MEVil from its use-cases).
>
> Yes we can? It's reasonable to see how arbitrary introspection could be u=
seful in various handwavy
> ways, and therefore how they can be used for undesirable applications, wh=
ile also not having an
> important use case it enables clearly defined, much less demonstrated.
>
> > However, given the uses of the Bitcoin chain today, it seems entirely p=
ossible (assuming
> > sufficient adoption) that we end up with a substantial MEVil risk with =
or without any
> > functionality expansion.
>
> Sure, but I=E2=80=99d argue that the presence of risk now is a reason to =
be more cautious about adding to
> it, rather than accepting it as inevitable.
>
> Best,
> Antoine
>
>
> On Tuesday, June 24th, 2025 at 12:00 PM, Matt Corallo <lf-lists@mattcoral=
lo.com> wrote:
>
> >
> >
> > Thanks, responding to one specific point:
> >
> > On 6/23/25 9:14 AM, 'Antoine Poinsot' via Bitcoin Development Mailing L=
ist wrote:
> >
> > > Yet another alternative is a set of more powerful capabilities, enabl=
ing the use cases that "commit to next transaction"
> > > and "verify a BIP340 signature for an arbitrary message" enable and m=
ore. For instance replacing "commit to the exact
> > > transaction which must spend this output" with "programmable introspe=
ction on the spending transaction's fields" has
> > > been considered. However this approach increases implementation compl=
exity and broadens the risk surface[^8]
> >
> >
> > Responded to below [1]
> >
> > > which
> > > warrants a compelling demonstration that arbitrary transaction intros=
pection does enable important use cases not
> > > achievable with more minimal capabilities.
> >
> >
> > I'm somewhat skeptical that showing this isn't rather simple, though I =
admit I've spent less time
> > thinking about these concepts. ISTM even something as simple as a rate-=
limit requires more
> > full-featured introspection than only "commit to the exact next transac=
tion" can provide. For
> > example, a trivial construction would be something which requires that =
transactions spending an
> > output have an output which claims at least Amount - Rate, which requir=
es both more full-featured
> > introspection as well as a bit of math. Given one of the loudest groups=
 advocating for the
> > additional features of CTV+CSFS are enterprise or large-value personal =
custody providers, it seems
> > somewhat of a loss to not work our way towards really basic features fo=
r this use-case.
> >
> > More generally, more full-featured introspection like TXHASH provides a=
 lot of flexibility in the
> > constructs people can build. For example, allowing BYO fees in the form=
 of an additional input +
> > output in a transaction, rather than fixing an anchor output in the fix=
ed "next transaction"
> > commitment to allow for fees (and then requiring the same additional in=
put + output later). There's
> > also open questions as to the incentive-compatibility of anchors in a w=
orld with expensive block
> > space, as OOB fees become much cheaper.
> >
> > Indeed, ISTM many use-cases for a construction like TXHASH become a lot=
 more substantial with Math
> > (though, again, I spend less time thinking about the use-cases of these=
 things than most, so I'm
> > sure others have more examples), I'm quite skeptical that just looking =
at an individual fork on
> > its own is the right benchmark. Sure, functionality in proposed changes=
 to Bitcoin's consensus need
> > to be well-justified, but they don't need to be well-justified purely o=
n their own. We add things
> > like OP_SUCCESS opcodes in soft forks specifically to expand the set of=
 things we can do later, not
> > specifically in this fork.
> >
> > If we assume that we end up wanting things like velocity limits (which =
I imagine we would?) then it
> > seems to me we should do a logical fork that adds features today, but w=
hich will allow us to make
> > minimal extensions in the future to further expand its use-cases later.=
 Taking a more myopic view of
> > the present and ignoring the future results in us doing one thing today=
, then effectively replacing
> > it later by adding more flexibility in a new opcode later, subsuming th=
e features of what we do
> > today. I don't see how this results in a net reduction in risk to Bitco=
in, rather just means more
> > total work and more cruft in Bitcoin's consensus.
> >
> > [1]
> >
> > Responding to the MEVil question OOO because I think the above should g=
o first :).
> >
> > Indeed, more flexible introspection provides for a difference in risk t=
o the system (though its
> > worth noting we cannot both argue that there is no "demonstrated utilit=
y" and that the utility of
> > a change is so substantially higher that it adds material risk to the s=
ystem in the form of MEVil
> > from its use-cases). However, given the uses of the Bitcoin chain today=
, it seems entirely possible
> > (assuming sufficient adoption) that we end up with a substantial MEVil =
risk with or without any
> > functionality expansion. This mandates a response from the Bitcoin deve=
lopment community in either
> > case, and I'm confident that response can happen faster than any reason=
able soft fork timeline.
> >
> > While its possible that existing CSV-based MEVil risk never grows beyon=
d its current anemic state
> > (due to preferences for stronger trust models from their users), and th=
at there's a particularly
> > clever design using expanded introspection that improves the trust mode=
l such that suddenly
> > CSV-based protocol use explodes, ISTM given the risk and the need to mi=
tigate it on its own, taking
> > decisions that are sub-optimal for Bitcoin's consensus on this basis is=
n't accomplishing much and
> > has real costs.
> >
> > Matt
> >
> > --
> > You received this message because you are subscribed to the Google Grou=
ps "Bitcoin Development Mailing List" group.
> > To unsubscribe from this group and stop receiving emails from it, send =
an email to bitcoindev+unsubscribe@googlegroups.com.
> > To view this discussion visit https://groups.google.com/d/msgid/bitcoin=
dev/8a9a2299-ab4b-45a4-8b9d-95798e6bb62a%40mattcorallo.com.
>
> --
> You received this message because you are subscribed to the Google Groups=
 "Bitcoin Development Mailing List" group.
> To unsubscribe from this group and stop receiving emails from it, send an=
 email to bitcoindev+unsubscribe@googlegroups.com.
> To view this discussion visit https://groups.google.com/d/msgid/bitcoinde=
v/73PXNVcmgiN2Kba63P2SRZfs42lvgME_8EF-DlYtkOSY8mLRxEXPEw5JAi5wtPU2MEMw1C6_E=
DFHKKrhaa1F53OgIJOcam-kbOUP3aG2_e0%3D%40protonmail.com.

--=20
You received this message because you are subscribed to the Google Groups "=
Bitcoin Development Mailing List" group.
To unsubscribe from this group and stop receiving emails from it, send an e=
mail to bitcoindev+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/=
CAEM%3Dy%2BVGE1SbuApOx0Y0jnAYrd-eu_kWFbQf%2BEHEHyv7seeGGw%40mail.gmail.com.