# Lightning Integration

Trustless atomic swaps between Citrea and Lightning Network are being actively implemented at the moment through third-party applications, such as [Atomiq](https://testnet4.atomiq.exchange). This will allow users of Citrea to pay Lightning invoices directly from the Citrea network or on- and off-ramp from Citrea without needing to leverage the Bitcoin base layer.

For both swap directions, the smart contract on Citrea simply emulates Lightning's HTLC. An LP (Liquidity Provider) behaves as a proxy on Lightning and it is responsible for all cross-network interactions - with liquidity maintained on both sides.

![Lightning Atomic Swap Diagram](https://4199298141-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FtFU3ZD7rSzMi2uz6wz9W%2Fuploads%2Fgit-blob-b6183bbcc524b2ccdfe8101bbf529814cbf9aefb%2Flightning_atomic_swap.png?alt=media)

For the path from Lightning to Citrea, here's a basic explanation:

* The receiver on the LN side creates an invoice and sends it to the sender on Citrea side.
* Sender locks cBTC on the HTLC contract with the invoice.
* LP makes the payment on LN on behalf of the sender.
* The preimage of the invoice gets revealed to the LP upon payment.
* LP uses the preimage to claim the cBTC from the HTLC contract.