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[2a00:1450:4864:20::643]) by gmr-mx.google.com with ESMTPS id ffacd0b85a97d-44640fb8469si210f8f.8.2026.04.27.10.59.48 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Apr 2026 10:59:48 -0700 (PDT) Received-SPF: pass (google.com: domain of aaron.recompile@gmail.com designates 2a00:1450:4864:20::643 as permitted sender) client-ip=2a00:1450:4864:20::643; Received: by mail-ej1-x643.google.com with SMTP id a640c23a62f3a-ba7a1cc0380so1731153766b.2 for ; Mon, 27 Apr 2026 10:59:48 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1777312788; cv=none; d=google.com; s=arc-20240605; b=aBdv1o/Vs8mK5BN6zetAQ7IdW9eh5RQ1ydbAnpGOJJ/YOLB0kmHoqwTRnDBcmFH6YC lViZTy/qWrChZgBLf916hBCvnj7PK8dAruSI8c7LR2sqsSfAY/TveK48e7bd5eqLmvY9 twv9HQzZQQmcgDnlB8IYasmMw6mRWAecSNFsmzM7hsNCkANe52TEc9RjVYasAEyMJV+8 aL0A4lJE+1NiZmc5Sg+uokTuAhfGVHuA53omjRhM66ceDL7V2hIJyKt6xN7v5dgHhvZ+ /IclZQPEPiIByUVyo5aUzC6t3tKikN8pkjcOigr4Yuk+IExJOTP0i8QpZKfzr/Lqua9E Kg0w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20240605; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:dkim-signature; bh=96gdRItzlJg8hUffUwrAtHdsFK+2nOjrJPIpbDJC4p4=; fh=/+5VU+jMurIbawBOBu+/nOs2RnNfi6Wci5vDLDLRL9Y=; b=RyuI5NBnF3GpH6I6Mbsr8KtbVvARnnfaIkieLo/qBPbHmjxLVJAsRKpgakahOMBWXm pO/C4XdIK3HT5433Y2JIJZRltGPoh5DtbMt2ydJcBiHO7jyluWKEt4Xfex0TMkStsf90 5DseORdmRfZaX5820dcbCzm44ZM0QH7A4H6JYAP347DFFcxWYu4xtUdccioz1roA0sSE CzflxcQGG4ioojZMqIrokVKuEBY78+C/ztPftPCqxmk5J3NvNKH0Kpyxaf6QGUK7zX3+ imanTJEVQa/c9lsu169sNymdomMO/5+JTnfAbZ/qrq/3b/DJ1RtYKAmb0upoigwqbB3A rJ9Q==; dara=google.com ARC-Authentication-Results: i=1; mx.google.com; arc=none X-Forwarded-Encrypted: i=1; AFNElJ8+6+YhqyqHiX6mbPcryfPcPjJVBRx+xnHCtVyfgX2oE0nmBWReyxYfgmBlmpjzLg0Q+MpO7IdjhzT7@googlegroups.com X-Gm-Gg: AeBDieuI8GcsNf9c0QQCZhww43VEwG0fImhTUkAIHPp+Uo0D8ZPQFadicdaoqkQvPOh ewKzOo3sKsVSDzp62inTF/tKI/KlDNPgd+b8H1dDv7SaVHZ70ILEv2LZlTvExaiv3c1ZqkbhlyG KCkYzulqFyjtFTCzJaOVZL4XeR6/4IpTiaBaexXPaZVPZSQQShw+a5RHMG/F2JG5g4pe6n/1Mqw jyJ15YNUT0028sA/x+exH1fTu3aogOtb4Wdj6sS6z6hWCmo7KXdOxUBlp59RY//jRYd4+Xsn4Gc 552L9tBvpMSTeFlrHIhGM6fH3S5+U4PHI2jJ9aLVQDrw1K+aMg== X-Received: by 2002:a17:907:608f:b0:ba8:9137:da5f with SMTP id a640c23a62f3a-ba89137e2cbmr1739457966b.32.1777312787915; Mon, 27 Apr 2026 10:59:47 -0700 (PDT) MIME-Version: 1.0 References: <494c0600-2daa-4500-8e49-bf36efbf2625n@googlegroups.com> In-Reply-To: From: "aaron.recompile" Date: Mon, 27 Apr 2026 10:59:34 -0700 X-Gm-Features: AVHnY4JSEmdJN96FhbrMuZD9RVhRGkvASbPxz8IJqxK6a1FT_Ezf4tEb2g3KjrA Message-ID: Subject: Re: [bitcoindev] Re: Subject: Eltoo / LN-Symmetry on Inquisition Signet: BIP 118 + 3-Round State Chain (APO+CTV) To: Sergio Demian Lerner Cc: Greg Sanders , Bitcoin Development Mailing List Content-Type: multipart/alternative; boundary="00000000000060e684065074e1e5" X-Original-Sender: aaron.recompile@gmail.com X-Original-Authentication-Results: gmr-mx.google.com; dkim=pass header.i=@gmail.com header.s=20251104 header.b=jIqeXmPW; arc=pass (i=1); spf=pass (google.com: domain of aaron.recompile@gmail.com designates 2a00:1450:4864:20::643 as permitted sender) smtp.mailfrom=aaron.recompile@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: X-Google-Group-Id: 786775582512 List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , X-Spam-Score: -0.5 (/) --00000000000060e684065074e1e5 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Following up on the APO+CTV state chain above =E2=80=94 I also ran a CSFS+CTV ladder variant on Inquisition signet, achieving the same Eltoo property (3 rounds of state updates, only the latest can settle) with two transactions instead of six. No APO, no CAT =E2=80=94 just already-activated CTV and CSFS. The compression comes from Jeremy Rubin's CSFS rekey ladder construction (https://rubin.io/bitcoin/2024/12/02/csfs-ctv-rekey-symmetry/)= , which makes each state hop a CSFS rekey =E2=80=94 a signature delegation, not a transaction =E2=80=94 collapsing the whole chain into one settlement witness. I made some engineering refinements to streamline the implementation. Confirmed Inquisition signet TxIDs, full construction, threat analysis, and witness layout: https://delvingbitcoin.org/t/eltoo-state-chain-on-signet-again-three-rounds= -two-transactions-csfs-ctv-with-rekey-and-ladder-no-cat/2430 Source code: https://github.com/aaron-recompile/btcaaron/tree/main/examples/eltoo Aaron On Tue, Apr 14, 2026 at 12:02=E2=80=AFPM Sergio Demian Lerner < sergio.d.lerner@gmail.com> wrote: > If you want to do have similar functionality to Eltoo without soft-forks, > you can use OTC-PCs: > > OTS-PC: OTS-based Payment Channels for the Lightning Network > https://arxiv.org/abs/2511.04021 > > regards, Sergio > > > On Tue, Apr 14, 2026 at 12:54=E2=80=AFPM Greg Sanders > wrote: > >> In case anyone is interested, a few months ago I resurrected my old >> ln-symmetry branch of CLN with various improvements and examples, thanks= to >> LLM doing the heavy lifting for revival. >> >> https://delvingbitcoin.org/t/ln-symmetry-project-recap/359/17 >> >> Aside from APO implementation, I also vibed a CSFS+TH+IK variant, though >> it cannot be tested on signet directly until OP_TEMPLATEHASH is activate= d. >> It's a drop-in replacement for CTV, if anyone cares to adapt it. >> >> Greg >> >> On Tuesday, April 14, 2026 at 5:18:24=E2=80=AFAM UTC-4 aaron.recompile w= rote: >> >>> Hi List, >>> >>> I ran a three-round Eltoo-style state chain on Bitcoin Inquisition 29.2 >>> signet using APO (BIP 118) for state updates and CTV for settlement. >>> Six transactions, all confirmed on-chain. >>> >>> An independent Python implementation of the BIP 118 sighash (Msg118 / >>> Ext118) was cross-validated against Inquisition's C++ consensus engine. >>> If the Python digest disagrees with Core's, the transaction is rejected= . >>> It wasn't. >>> >>> Construction >>> ------------ >>> Each state UTXO is a three-leaf Taproot tree: >>> >>> leaf 1 -- ctv_uhpo: OP_CHECKTEMPLATEVERIFY >>> leaf 2 -- apo_update: <0x01||xonly> OP_CHECKSIG (BIP 118) >>> leaf 3 -- csv_escape: OP_CHECKSEQUENCEVERIFY OP_DROP >>> OP_CHECKSIG >>> >>> CTV locks each state's payout distribution >>> as a template hash. APO rebinding advances state. When an APO update >>> spends state vN, vN's CTV leaf >>> loses its only viable input and can never settle. Only the latest state >>> can produce a valid settlement. This is the Eltoo invariant, executed >>> end-to-end with current tooling. >>> >>> Confirmed txids (Inquisition signet) >>> ------------------------------------- >>> Fund =E2=86=92 State v1: >>> 386dbb6aa23fcc35a69d34e3c0f760b185482467abc936196d3def19d54a9c41 >>> APO update v1 =E2=86=92 v2: >>> 096e31ccbd8f5460b2730ec4f757ee1b01acf9dde3e3b8cb55fbb534fe195601 >>> APO update v2 =E2=86=92 v3: >>> 091309b73e299436ff12fceda7e54e28c6f1817fdf3405bca3343ad15198d7f6 >>> CTV settlement: >>> 13957f49d01aa21ed2aa28df7aa78f357d51a2a2fbfb434af05fdc75ad0ff9b7 >>> >>> Rebind A (signed): >>> 03c0577c1d47da32804d098187644d0eee18b448aded2f427cd02193c070f3a4 >>> Rebind B (witness copied): >>> 46091190c74d8fd4b39be67a2e945a19b021850e7f8d9e378f5eb11722ae1a43 >>> >>> Rebind A and B share an identical witness stack =E2=80=94 same 65-byte = signature >>> (sighash flag 0x41), same leaf script, same control block =E2=80=94 spe= nding two >>> different UTXOs without re-signing. Outputs remain committed: changing >>> the output address in Rebind B causes script verification failure. >>> The last two transactions are a standalone rebinding demonstration, >>> not part of the state chain above. >>> >>> Links >>> ------ >>> BIP 118 signing primitive and rebinding proof (Delving Bitcoin): >>> >>> https://delvingbitcoin.org/t/bip-118-signing-from-scratch-on-chain-rebi= nding-proof/2411 >>> >>> Eltoo state chain construction (Delving Bitcoin): >>> >>> https://delvingbitcoin.org/t/eltoo-state-chain-on-signet-three-rounds-s= ix-transactions-apo-ctv/2413 >>> >>> Source code (btcaaron, examples/braidpool/): >>> https://github.com/aaron-recompile/btcaaron >>> >>> Happy to discuss the construction or the CTV+CSFS gap. >>> >>> Aaron Zhang >>> >> -- >> You received this message because you are subscribed to the Google Group= s >> "Bitcoin Development Mailing List" group. >> To unsubscribe from this group and stop receiving emails from it, send a= n >> email to bitcoindev+unsubscribe@googlegroups.com. >> To view this discussion visit >> https://groups.google.com/d/msgid/bitcoindev/494c0600-2daa-4500-8e49-bf3= 6efbf2625n%40googlegroups.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/bitcoindev/CAKzdR-ok1jwtXOYaAPBw1fhpavL= %3DP%2B2jsT%2BVcKc9OwW6bhpRFw%40mail.gmail.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/= CAEmKuUEw6YFcrDoVRz4fwjta3sREErSvx9S4UHQ%2B1S5B%3DAfbAg%40mail.gmail.com. --00000000000060e684065074e1e5 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Following up on the APO+CTV state chain above =E2=80=94 I = also ran a
CSFS+CTV ladder variant on Inquisition signet, achieving the = same
Eltoo property (3 rounds of state updates, only the latest can
s= ettle) with two transactions instead of six. No APO, no CAT =E2=80=94
ju= st already-activated CTV and CSFS.

The compression comes from Jeremy= Rubin's CSFS rekey ladder
construction (https://rubin.io/bitcoin/2024= /12/02/csfs-ctv-rekey-symmetry/),
which makes each state hop a CSFS = rekey =E2=80=94 a signature
delegation, not a transaction =E2=80=94 coll= apsing the whole chain into
one settlement witness. I made some engineer= ing refinements to streamline the implementation.

Confirmed Inquisit= ion signet TxIDs, full construction, threat
analysis, and witness layout= :
https://delvingbitcoin.org/t/eltoo-state-chain-on-signet-again-three-rou= nds-two-transactions-csfs-ctv-with-rekey-and-ladder-no-cat/2430

= Source code:
https://github.com/aaron-recompile/btcaaron/tree/main= /examples/eltoo

Aaron


On Tue, Apr 14, 2= 026 at 12:02=E2=80=AFPM Sergio Demian Lerner <sergio.d.lerner@gmail.com> wrote:
If you want to= do have similar functionality to Eltoo without soft-forks, you can use OTC= -PCs:=C2=A0

OTS-PC: OTS-based Payment Channels for the Lightnin= g Network

On Tue, Apr 14, 2026 at 12:54=E2=80=AFPM= Greg Sanders <gsanders87@gmail.com> wrote:
In case anyone is interested, a few months ago I resur= rected my old ln-symmetry branch of CLN with various improvements and examp= les, thanks to LLM doing the heavy lifting for revival.


Aside from APO implementation, I also vibe= d a CSFS+TH+IK variant, though it cannot be tested on signet directly until= OP_TEMPLATEHASH is activated. It's a drop-in replacement for CTV, if a= nyone cares to adapt it.

Greg

=
On Tuesda= y, April 14, 2026 at 5:18:24=E2=80=AFAM UTC-4 aaron.recompile wrote:
Hi List,

I ran a three-round Eltoo-style state chain on Bitcoin Inquisition 29.2
signet using APO (BIP 118) for state updates and CTV for settlement.
Six transactions, all confirmed on-chain.

An independent Python implementation of the BIP 118 sighash (Msg118 /
Ext118) was cross-validated against Inquisition's C++ consensus eng= ine.
If the Python digest disagrees with Core's, the transaction is reje= cted.
It wasn't.

Construction
------------
Each state UTXO is a three-leaf Taproot tree:

leaf 1 -- ctv_uhpo: <template_hash> OP_CHECKTEMPLATEVERIFY
leaf 2 -- apo_update: <0x01||xonly> OP_CHECKSIG (BIP 118)
leaf 3 -- csv_escape: <sequence> OP_CHECKSEQUENCEVERIFY OP_DROP
<pubkey> OP_CHECKSIG

CTV locks each state's payout distribution
as a template hash. APO rebinding advances state. When an APO update
spends state vN, vN's CTV leaf
loses its only viable input and can never settle. Only the latest state
can produce a valid settlement. This is the Eltoo invariant, executed
end-to-end with current tooling.

Confirmed txids (Inquisition signet)
-------------------------------------
Fund =E2=86=92 State v1:
386dbb6aa23fcc35a69d34e3c0f760b185482467abc936196d3def19d54a9c41
APO update v1 =E2=86=92 v2:
096e31ccbd8f5460b2730ec4f757ee1b01acf9dde3e3b8cb55fbb534fe195601
APO update v2 =E2=86=92 v3:
091309b73e299436ff12fceda7e54e28c6f1817fdf3405bca3343ad15198d7f6
CTV settlement: 13957f49d01aa21ed2aa28df7aa78f357d51a2a2fbfb434af05fdc7= 5ad0ff9b7

Rebind A (signed):
03c0577c1d47da32804d098187644d0eee18b448aded2f427cd02193c070f3a4
Rebind B (witness copied):
46091190c74d8fd4b39be67a2e945a19b021850e7f8d9e378f5eb11722ae1a43

Rebind A and B share an identical witness stack =E2=80=94 same 65-byte = signature
(sighash flag 0x41), same leaf script, same control block =E2=80=94 spe= nding two
different UTXOs without re-signing. Outputs remain committed: changing
the output address in Rebind B causes script verification failure.
The last two transactions are a standalone rebinding demonstration,
not part of the state chain above.

Links
------
BIP 118 signing primitive and rebinding proof (Delving Bitcoin):
https://del= vingbitcoin.org/t/bip-118-signing-from-scratch-on-chain-rebinding-proof/241= 1

Eltoo state chain construction (Delving Bitcoin):
https://delvingbitcoin.org/t/eltoo-state-chain-on-signet-three-rounds-six-= transactions-apo-ctv/2413

Source code (btcaaron, examples/braidpool/):
https://github.com/aaron-recompile/btcaaron

Happy to discuss the construction or the CTV+CSFS gap.

Aaron Zhang

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