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From: Ademan <ademan555@gmail.com>
Date: Wed, 9 Jul 2025 15:14:02 -0500
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Subject: Re: [bitcoindev] A Taproot-native (re-)bindable transaction bundle proposal
To: Rijndael <rot13maxi@gmail.com>
Cc: Greg Sanders <gsanders87@gmail.com>, 
	Bitcoin Development Mailing List <bitcoindev@googlegroups.com>
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Isn't it indirectly committed to by sha_sequences?

On Wed, Jul 9, 2025 at 3:09=E2=80=AFPM Rijndael <rot13maxi@gmail.com> wrote=
:

> Hey Greg,
>
> The CTV commitment includes the number of inputs. I notice that the
> TEMPLATEHASH commitment does not. What=E2=80=99s the rationale there?
>
> Thanks,
>
> Rijndael
>
> On Jul 9, 2025, at 2:19=E2=80=AFPM, Greg Sanders <gsanders87@gmail.com> w=
rote:
>
> Hello all,
>
> This is a bit of a follow-up from "What's a good stopping point? ...
> CTV/CSFS..." from [^1]
>
> > There has been several objections to this proposal, which we can group
> into three categories:
> exploration of alternatives, demonstration of usage, and design of the
> operations to achieve these capabilities
>
> For this e-mail I would like to address the third point proactively:
> design of the operations to achieve these capabilities.
>
> Antoine Poinsot, Steven Roose, and I have been working on a familiar, yet
> concrete technical proposal that focuses on three well-understood
> capabilities:
>
> 1. "Next transaction" capability, ala BIP119
> 2. "Verify signature of message on stack", ala BIP348
> 3. "Push taproot internal key onto stack", ala BIP349
>
> These first two capabilities can offer radical simplifications
> to well-understood systems when combined. The third is a simple
> update that dovetails with the first two.
>
> The BIP text is here(
> https://github.com/instagibbs/bips/blob/bip_op_templatehash/bip-templateh=
ash-csfs-ik.md)
> and PR here(https://github.com/instagibbs/bips/pull/1), with full
> motivation for this particular bundle and rationale discussing
> alternatives. Our main contribution is a fully specified `OP_TEMPLATEHASH=
`
> as a drop-in replacement for BIP119 `OP_CHECKTEMPLATEVERIFY`.
> `OP_TEMPLATEHASH` is a simpler and more modern implementation of the "nex=
t
> transaction" capability. It differs in committing to the Taproot annex an=
d
> being otherwise Taproot native, which allows us to:
>
> - Use the `OP_SUCCESS` upgrade hooks in place of legacy `OP_NOP`s and be
> able to push the template hash on the stack making the flagship use case =
of
> rebindable signatures more efficient.
> - Re-use the existing pre-computed Taproot sighash fields only instead of
> introducing new ones (substantially simplifying the implementation and
> review of the specifications).
> - Not commit to the spending transaction's scriptSigs (which are both
> unecessary and may incentivize ad-hoc uses of legacy input scripts as
> programs).
> - Not unnecessarily modify the less well-understood legacy Script.
>
> Another notable difference is the lack of "bare CTV" analogue, which is
> implemented here(https://github.com/instagibbs/bitcoin/tree/p2th) but
> left out of the bundle due to lack of demonstrated utility.
>
> The BIP for `OP_TEMPLATEHASH` is here(
> https://github.com/instagibbs/bips/blob/bip_op_templatehash/bip-templateh=
ash.md)
> and a complete implementation is provided here(
> https://github.com/instagibbs/bitcoin/pull/3). The bundle itself is
> heavily inspired by "LNHANCE"(
> https://delvingbitcoin.org/t/lnhance-bips-and-implementation/376).
>
> We are hopeful that an opcode/implementation-focused discussion can be he=
ld
> concurrently with other efforts such as discussions as to whether
> or not this capability set is a good stopping point, including whether
> this bundle is worth implementing on its own at all, as well as what
> level of assurances we should have as far as tooling and proof of concept=
s
> is concerned.
>
> Best,
> Greg
>
> (1) https://groups.google.com/g/bitcoindev/c/-qJc1EWQzY0
>
> --
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becc3412cn%40googlegroups.com?utm_medium=3Demail&utm_source=3Dfooter>
> .
>
>
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<div dir=3D"ltr">Isn&#39;t it indirectly committed to by sha_sequences?</di=
v><br><div class=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" cla=
ss=3D"gmail_attr">On Wed, Jul 9, 2025 at 3:09=E2=80=AFPM Rijndael &lt;<a hr=
ef=3D"mailto:rot13maxi@gmail.com">rot13maxi@gmail.com</a>&gt; wrote:<br></d=
iv><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bord=
er-left:1px solid rgb(204,204,204);padding-left:1ex"><div>Hey Greg,<div><br=
></div><div>The CTV commitment includes the number of inputs. I notice that=
 the TEMPLATEHASH commitment does not. What=E2=80=99s the rationale there?<=
/div><div><br></div><div>Thanks,=C2=A0</div><div><br></div><div>Rijndael<br=
 id=3D"m_2949184547047721100lineBreakAtBeginningOfMessage"><div><br><blockq=
uote type=3D"cite"><div>On Jul 9, 2025, at 2:19=E2=80=AFPM, Greg Sanders &l=
t;<a href=3D"mailto:gsanders87@gmail.com" target=3D"_blank">gsanders87@gmai=
l.com</a>&gt; wrote:</div><br><div>Hello all,<br><br>This is a bit of a fol=
low-up from &quot;What&#39;s a good stopping point? ... CTV/CSFS...&quot; f=
rom [^1]<br><br>&gt; There has been several objections to this proposal, wh=
ich we can group into three categories:<br>exploration of alternatives, dem=
onstration of usage, and design of the operations to achieve these capabili=
ties<br><br>For this e-mail I would like to address the third point proacti=
vely: design of the operations to achieve these capabilities.<br><br>Antoin=
e Poinsot, Steven Roose, and I have been working on a familiar, yet concret=
e technical proposal that focuses on three well-understood capabilities:<br=
><br>1. &quot;Next transaction&quot; capability, ala BIP119<br>2. &quot;Ver=
ify signature of message on stack&quot;, ala BIP348<br>3. &quot;Push taproo=
t internal key onto stack&quot;, ala BIP349<br><br>These first two capabili=
ties can offer radical simplifications<br>to well-understood systems when c=
ombined. The third is a simple<br>update that dovetails with the first two.=
<br><br>The BIP text is here(<a href=3D"https://github.com/instagibbs/bips/=
blob/bip_op_templatehash/bip-templatehash-csfs-ik.md" target=3D"_blank">htt=
ps://github.com/instagibbs/bips/blob/bip_op_templatehash/bip-templatehash-c=
sfs-ik.md</a>) and PR here(<a href=3D"https://github.com/instagibbs/bips/pu=
ll/1" target=3D"_blank">https://github.com/instagibbs/bips/pull/1</a>), wit=
h full motivation for this particular bundle and rationale discussing alter=
natives. Our main contribution is a fully specified `OP_TEMPLATEHASH` as a =
drop-in replacement for BIP119 `OP_CHECKTEMPLATEVERIFY`. `OP_TEMPLATEHASH` =
is a simpler and more modern implementation of the &quot;next transaction&q=
uot; capability. It differs in committing to the Taproot annex and being ot=
herwise Taproot native, which allows us to:<div><br>- Use the `OP_SUCCESS` =
upgrade hooks in place of legacy `OP_NOP`s and be able to push the template=
 hash on the stack making the flagship use case of rebindable signatures mo=
re efficient.<br>- Re-use the existing pre-computed Taproot sighash fields =
only instead of introducing new ones (substantially simplifying the impleme=
ntation and review of the specifications).<br>- Not commit to the spending =
transaction&#39;s scriptSigs (which are both unecessary and may incentivize=
 ad-hoc uses of legacy input scripts as programs).<br>- Not unnecessarily m=
odify the less well-understood legacy Script.<br><br>Another notable differ=
ence is the lack of &quot;bare CTV&quot; analogue, which is implemented her=
e(<a href=3D"https://github.com/instagibbs/bitcoin/tree/p2th" target=3D"_bl=
ank">https://github.com/instagibbs/bitcoin/tree/p2th</a>) but left out of t=
he bundle due to lack of demonstrated utility.<br><br>The BIP for `OP_TEMPL=
ATEHASH` is here(<a href=3D"https://github.com/instagibbs/bips/blob/bip_op_=
templatehash/bip-templatehash.md" target=3D"_blank">https://github.com/inst=
agibbs/bips/blob/bip_op_templatehash/bip-templatehash.md</a>) and a complet=
e implementation is provided here(<a href=3D"https://github.com/instagibbs/=
bitcoin/pull/3" target=3D"_blank">https://github.com/instagibbs/bitcoin/pul=
l/3</a>). The bundle itself is heavily inspired by &quot;LNHANCE&quot;(<a h=
ref=3D"https://delvingbitcoin.org/t/lnhance-bips-and-implementation/376" ta=
rget=3D"_blank">https://delvingbitcoin.org/t/lnhance-bips-and-implementatio=
n/376</a>).<br><br>We are hopeful that an opcode/implementation-focused dis=
cussion can be held<br>concurrently with other efforts such as discussions =
as to whether<br>or not this capability set is a good stopping point, inclu=
ding whether<br>this bundle is worth implementing on its own at all, as wel=
l as what<br>level of assurances we should have as far as tooling and proof=
 of concepts<br>is concerned.<br><br>Best,<br>Greg<br><br>(1) <a href=3D"ht=
tps://groups.google.com/g/bitcoindev/c/-qJc1EWQzY0" target=3D"_blank">https=
://groups.google.com/g/bitcoindev/c/-qJc1EWQzY0</a></div><div><br></div>

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