From bastien at acinq.fr  Wed Sep 22 06:58:18 2021
From: bastien at acinq.fr (Bastien TEINTURIER)
Date: Wed, 22 Sep 2021 08:58:18 +0200
Subject: [Lightning-dev] Opening balanced channels using PSBT
In-Reply-To: <CAFoQ5ePhre+Y-fKPdfYH0QFTXMY4nEE1bSbYTtF4wH_khEFz2g@mail.gmail.com>
References: <CAFoQ5ePhre+Y-fKPdfYH0QFTXMY4nEE1bSbYTtF4wH_khEFz2g@mail.gmail.com>
Message-ID: <CACdvm3PAkigNdifeLRms8Bkuib7+eVCCT9RS1TkzN=5xH=XpSA@mail.gmail.com>

Hi,

This is exactly what the dual funding proposal provides:
https://github.com/lightningnetwork/lightning-rfc/pull/851

Cheers,
Bastien

Le mer. 22 sept. 2021 ? 07:29, Ole Henrik Skogstr?m <oleskogstrom at gmail.com>
a ?crit :

> Hi
>
> I have found a way of opening balanced channels using LND's psbt option
> when opening channels. What I'm doing is essentially just joining funded
> PSBTs before signing and submitting them. This makes it possible to open a
> balanced channel between two nodes or open a ring of balanced channels
> between multiple nodes (ROF).
>
> I found this interesting, however I don't know if this is somehow unsafe
> or for some other reason a bad idea. If not, then it could be an
> interesting alternative to only being able to open unbalanced channels.
>
> To do this efficiently, nodes need to collaborate by sending PSBTs back
> and forth to each other and doing this manually is a pain, so if this makes
> sense to do, it would be best to automate it through a client.
>
> ----------------------
> --- Here is an example of the complete flow for a single channel:
> ----------------------
>
> ** Node A: generates a new address and sends address to Node B *(lncli
> newaddress p2wkh)
>
> ** Node A starts an Interactive channel **open** to Node B* *using psbt*
> (lncli openchannel --psbt <node_b_pubkey> 2000000 1000000)
>
> ** Node A funds the channel address *(bitcoin-cli walletcreatefundedpsbt
> [] '[{"<channel_address>":0.02}]')
>
> ** Node B funds the refund transaction to Node A and sends PSBT back to
> Node A (*bitcoin-cli walletcreatefundedpsbt []
> '[{"<node_a_return_address>":0.01}]')
>
> * *Node A joins the two PSBTs and sends it back to Node B (*bitcoin-cli
> joinpsbts '["<channel_open_psbt>", "<node_b_return_to_node_a_psbt>"]')
>
> ** Node B verifies the content and signs the joined PSBT before sending it
> back to Node A *(bitcoin-cli walletprocesspsbt <joined_psbt>)
>
> ** Node A: Verifies the content and signs the joined PSBT *(bitcoin-cli
> walletprocesspsbt <joined_psbt>)
>
> ** Node A: Completes channel open by publishing the fully signed PSBT*
>
>
> ----------------------
> --- Here is an example of the complete flow for a ring of channels between
> multiple nodes:
> ----------------------
>
> ** Node A starts an Interactive open channel to Node B using psbt* (lncli
> openchannel --psbt --no_publish <node_b_pubkey> 2000000 1000000)
> ** Node A funds the channel address* (bitcoin-cli walletcreatefundedpsbt
> [] '[{"<channel_address>":0.02}]')
>
> ** Node B starts an Interactive open channel to Node C using psbt* (lncli
> openchannel --psbt --no_publish <node_b_pubkey> 2000000 1000000)
> ** Node B funds the channel address* (bitcoin-cli walletcreatefundedpsbt
> [] '[{"<channel_address>":0.02}]')
>
> ** Node C starts an Interactive open channel to Node A using psbt* (lncli
> openchannel --psbt <node_b_pubkey> 2000000 1000000)
> ** Node C funds the channel address *(bitcoin-cli walletcreatefundedpsbt
> [] '[{"<channel_address>":0.02}]')
>
> ** Node B and C sends Node A their PSBTs*
>
> ** Node A joins all the PSBTs* (bitcoin-cli joinpsbts
> '["<A_funded_channel_psbt>", "<B_funded_channel_psbt>",
> "<C_funded_channel_psbt>"]')
>
> Using (bitcoin-cli walletprocesspsbt <joined_psbt>):
>
>
>
> ** Node A verifies and signs the PSBT and sends it to Node B (1/3
> signatures)* Node B verifies and signs the PSBT and sends it to Node C (2/3
> signatures)* Node C verifies and signs the PSBT (3/3 signatures) before
> sending it to Node A and B.*
>
>
> ** Node A completes channel open (no_publish)* Node B completes channel
> open (no_publish)* Node C completes channel open and publishes the
> transaction.*
>
> --
> Ole Henrik Skogstr?m
>
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> Lightning-dev at lists.linuxfoundation.org
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>
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