Trustless Lightning-to-Bitcoin Swap? – Bitcoin Stack Change

I came upon methods to flip round these steps for the ‘reverse’ case.

Within the ahead case, the Lightning bill doesn’t must be generated by the Payer, however could be by a 3rd get together, as described within the query. Whether it is generated by the Payer, and there are solely two events concerned, then that case could be ‘turned’ round for the reverse, LN->BTC case, with very related vault utilization.

First I re-describe the ahead case, when it comes to two events, after which I describe the trustless answer for the reverse case. Observe that I name the swapper actor Shopper (as an alternative of Payer).

Ahead case (BTC->LN):

• Actors: Shopper, who desires to swap onchain BTC to Lightning BTC, and Supplier of the swap service

Steps:

1. Shopper creates a Lightning bill it needs to be paid, with desired quantity.
2. Shopper initiates a request to the Supplier, with the small print of the bill (quantity, fee hash, timeouts, and many others.) and its personal pubkey.
3. Supplier units up a ‘vault’ BTC tackle, managed by a script, permitting to be spent by somebody who can show that the LN bill has been paid (regular department), or by the Shopper after a while (timeout refund department). Supplier communicates the vault tackle, the script and the BTC quantity it expects to Shopper.
4. Shopper verifies the script: that it has the correct quantity, and it has a timeout department with its personal pubkey.
5. Shopper performs the on-chain BTC fee to the vault tackle.
6. Supplier observes the fee, waits for affirmation, verifies it.
7. Supplier pays the LN bill (from its LN funds).
8. As soon as the bill is paid, Supplier transfers the BTC from the vault to an tackle of its personal management.

Finish consequence: LN bill is paid, Shopper has much less BTC and extra LN-BTC, Supplier has much less LN-BTC however extra BTC.

Right here is the detailed description of the reverse, LN->BTC case:

Reverse case (LN->BTC):

Actors: Shopper, who desires to swap Lightning BTC to onchain BTC, and Supplier of the swap service.

Steps:

1. Shopper initiates a request to the Supplier, with the specified quantity.
2. Supplier creates a Lightning bill.
3. Supplier units up a ‘vault’ BTC tackle, managed by a script, permitting to be spent by somebody who can show that the LN bill has been paid (regular department), or by itself after a while (timeout refund department).
4. Supplier makes BTC fee to the vault tackle.
5. Supplier communicates the lightning bill to Shopper (with out the fee secret, after all), the vault tackle and script.
6. Shopper verifies the vault, that it has payout department secured by the fee hash of the bill.
7. Shopper verifies that the vault has the correct quantity of BTC, waits for affirmation if wanted.
8. Shopper pays the Lighting bill.
9. Now within the possession of the fee secret, Shopper transfers the BTC from the vault to itself.

Finish consequence: LN bill is paid, Shopper has much less LN-BTC and extra BTC, Supplier has much less BTC however extra LN-BTC.

Some notes:

• In each circumstances it’s the Supplier who units up the vault.
• I didn’t increase on the fallback case (ahead case: the shopper can get better its BTC if Supplier fails to satisfy; reverse case: Supplier can get better its BTC if Shopper fails to pay).
• The Supplier can add some additional service payment, the Shopper is conscious of the elevated quantity earlier than paying, however this ought to be agreed/communicated earlier than.
• Within the ahead case the Lightning bill could be created upfront by a 3rd get together, and the Shopper can organize that bill to be paid instantly, e.g. when desirous to pay for an bill of a web based service provider (this use case variant is within the authentic query). Within the reverse case this isn’t attainable (to pay BTC on to the third get together), because the BTC recipient should do a particular operation (transferring the BTC from the vault tackle).