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Bitcoin Wallets

Bitcoin Wallets

Signing a DLC requires functionality not always present in existing Bitcoin wallets on the market. To fulfill this requirement, DLC.Link will provide open-source libraries in the Rust and JavaScript programming languages.
DLC transactions are handled by two parties, an offeror and an acceptor. In our current setup, the Bitcoin wallet acts as the acceptor and the dApp acts as the offeror. It is the Bitcoin wallet that handles accepting signatures, building and signing Contract Execution Transactions (CETs), and broadcasting onto the BTC blockchain.

Instantiaton of the Javascript DLC Interface

First install the DLC interface using npm:
npm install dlc-wasm-wallet
Then import the DLC interface into your project:
import { JsDLCInterface } from 'dlc-wasm-wallet';
Before using the Discreet Log Contract (DLC) interface to establish a DLC, you must initiate it with specific information. This includes data provided by a Bitcoin wallet, such as the user's private key, address, the selected Bitcoin network, it's API endpoint, and the URLs for the attestors' endpoints.
After the specific information is provided, you can instantiate the DLC interface with the following function called new:
interface JsDLCInterface {
new (
userPrivateKey: string, // The user's private key.
userAddress: string, // The user's address.
bitcoinNetwork: string, // The Bitcoin network.
bitcoinNetworkAPI: string, // The Bitcoin network API endpoint.
attestorURLs: string // An array of attestor API endpoints (string[]), which has been converted into a JSON string.
): JsDLCInterface;
Note Ensure that all the necessary fields are JSON-stringified before utilizing them as param, as the interface operates using JSON format.
Under the hood, a DlcManager instance is created.
The DlcManager is used to manage the life cycle of decentralized lending and borrowing contracts on a blockchain network. It has several methods that handle different stages of the contract life cycle, such as creating, accepting, signing, and rejecting contracts.

Bitcoin Lending Flow

Step 1 | Receive Offer

An offer will be received once the contract is set up in the dApp, sent to the dApp’s Router Wallet (offeror’s wallet), validated, and signed by the offeror. An offer will include a contract that already contains the attestor announcements and offeror parameters.
If you are not familiar with how to request an offer from the dApp, please refer to the Interacting with Bitcoin Contracts section.
After the offer is received, the Bitcoin Wallet can review the contract and decide whether to accept or reject it.

Step 2 | Accept Offer

To accept a Bitcoin Contract Offer, you must utilize the accept_offer() function, which accepts a Bitcoin Contract offer in JSON format as a param.
The accept_offer() function of the DLC interface is invoked with a temporary contract id when the user accepts the contract.
const bitcoinContractJSON = JSON.stringify(bitcoinContractOffer);
const acceptedBitcoinContract = await bitcoinContractInterface.accept_offer(bitcoinContractJSON);
Once accepted, the DlcManager verifies the availability of sufficient utxos, gathers them, and constructs a refund signature along with a constant id. It then ensures that all CETs are signed by the involved parties and attestor(s). Finally, it saves the contract in the cloud storage, associating it with the user's public key.

Step 3 | Send Accepted Offer to Router Wallet

Before signing and broadcasting a Bitcoin Contract, you must send the accepted Bitcoin Contract Offer to the dApp's Router Wallet. To do so, you should ulitize a function similar to the following:
async function sendAcceptedBitcoinContractOfferToRouterWallet(
acceptedBitcoinContractOffer: string,
counterpartyWalletURL: string
) {
return fetch(`${counterpartyWalletURL}/offer/accept`, {
method: 'put',
body: JSON.stringify({
acceptMessage: acceptedBitcoinContractOffer,
headers: { 'Content-Type': 'application/json' },
}).then((res) => res.json());
const signedBitcoinContract = await sendAcceptedBitcoinContractOfferToRouterWallet(
If the Router Wallet succesfully validates the accepted Bitcoin Contract offer, it will sign the contract and return it to the Bitcoin Wallet.

Step 4 | Sign and Broadcast

To sign and broadcast a Bitcoin Contract, you must utilize the countersign_and_broadcast() function, which accepts a signed Bitcoin Contract in JSON format as a param.
const signedBitcoinContractJSON = JSON.stringify(signedBitcoinContract);
const txID = await bitcoinContractInterface.countersign_and_broadcast(signedBitcoinContractJSON);
This function handles signing and verifying the contract signatures, and updates the contract in the cloud-storage.
After the function is executed, the Bitcoin Wallet will broadcast the contract onto the Bitcoin blockchain. It returns the transaction ID of the contract, which you can use to track the transaction on the blockchain.