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Subject: Re: [bitcoin-dev] Payjoin2swap: Enabling Payjoin Without Merchant
Purchases
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Good morning list,
I observe that if the Lightning Network supports:
1. Wumbo channels (>167.772215mBTC channels)
2. Dual-funded channels
Then payjoin2swap is implementable using LN operations.
Given two UTXOs V and W you want to transfer some value S from V to W.
1. Connect to an LN node on Tor and listen to gossip, then disconnect.
2. Create two fake node addresses (A and B) and assign a unique Tor hidden=
service to each.
3. Select two actual LN nodes with long uptime (use the lifetime of the ch=
annels they have as a rough estimate) and a short distance between them wit=
h good capacity and many alternate routes between them.
4. Connect A to one node and create a channel using V.
Indicate that the channel should be unpublished (the LN protocol has a =
flag existing for this already).
Publishing channels is good for privacy if you intend to stay long on L=
N (it invites "normal" traffic to hide your own payments in), but we do not=
intend to stay long on LN here, so keep the channels unpublished.
5. Connect B to the other node and create a channel with dual-funding, req=
uesting at least S from the other node to put in the channel, using W as yo=
ur own UTXO.
Again indicate the channel should be unpublished.
6. Transfer S satoshi over LN from the channel of A to the channel of B.
7. Cooperatively close both channels.
It is possible to time the closes to be some blocks apart to make them =
harder for blockchain analysis to link.
This rides payjoin2swap on top of existing infrastructure.
The drawback is that it is unlikely that existing LN implementations will a=
pply ZeroLink for onchain funds, since much of the privacy on LN is with pa=
ying over the long-lived offchain channels.
This can erode privacy if either of the nodes you connect to uses the resul=
t of the cooperative closes to later fund a published channel, possibly mix=
ing it with other coins of their own.
Regards,
ZmnSCPxj
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