Description

Solidity code and scripts for deploying and interacting with MintContract and BurnContract on Sepolia network.

Quick start

The first things you need to do are cloning this repository and installing its dependencies (you may need to nvm use version > 16):

npm install

Compile smartcontracts

npx hardhat compile

Now you can run script in the scripts folder using:

npx hardhat run scripts/script-name.js --network sepolia

Sepolia Deployed Contract

Contract	Address
sBTC	0xa32e5903815476Aff6E784F5644b1E0e3eE2081B
AxelarGateway	0xd70943944567979d99800DD14b441B1D3A601A1D
GasService	0xbE406F0189A0B4cf3A05C286473D23791Dd44Cc6
AxelarAuthWeighted	0x71b7B290B14D7A8EB8071e35e3457b192b4a7fB6
MintContract	0x768E8De8cf0c7747D41f75F83C914a19C5921Cf3
BurnContract	0x44dD1420Af56740ACeb697538227A9A787067786

Scripts explain

Deploy contract

Scripts to deploy smart contract usually begin with this pattern:

const gatewayAddress = "0x1811AE0B97479b77258CF8aAda7768aB74e21aE9"; // Params passed to constructor of BurnContract
const gasServiceAddress = "0xbE406F0189A0B4cf3A05C286473D23791Dd44Cc6"; // Params passed to constructor of BurnContract
const sbtcAddress = "0xa32e5903815476Aff6E784F5644b1E0e3eE2081B"; // Params passed to constructor of BurnContract

const BurnContract = await ethers.getContractFactory("BurnContract");
const burnContract = await BurnContract.deploy(
  gatewayAddress,
  gasServiceAddress,
  sbtcAddress
);
await burnContract.deployed();

At the end of the deployment script, the contract abi and address will be saved to the abis folder.

saveABI([
  {
    name: "BurnContract",
    address: burnContract.address,
  },
]);

Interaction with deployed contracts

Scripts to test or interact with smart contract usually begin with this pattern:

const contractName = "BurnContract";
const contractArtifact = require(`../artifacts/contracts/${contractName}.sol/${contractName}.json`);
const contractABI = contractArtifact.abi;
const burnContract = new ethers.Contract(
  "0x6F111e169710C6c3a33948c867aE425A74cDa1a3", // TODO: update BurnContract address
  contractABI,
  signer
);

This code is used to get the contract instance by contract ABI and address.
When running any scripts, check the contract address and update it if necessary.

When calling get methods of a contract (public attributes or view functions), you just need to:

const result = await burnContract.getSomeValue();

However, when calling set methods of a contract (functions that change the state of the contract), you need to sign the transaction before sending it:

const tx = await burnContract.setSomeValue(newValue);
await tx.wait();

Details of Axelar related contracts

Contracts deployed

In order to make the ethereum-side of the bridge work, we need to deploy these main contracts:

1. AxelarGateway: This contract is the main contract that will be used to interact with the Axelar network. The constructor of this contract take the address of the AxelarAuthWeighted contract as a parameter, so that we need to deploy the AxelarAuthWeighted contract first.
2. AxelarAuthWeighted: This contract is used to manage the operatorship of the Axelar network. It also define logic to validate the signatures of messages receiving from the Axelar network.
3. MintContract: This contract implement the AxelarExecutable interface. The constructor of this contract take the address of the AxelarGateway, GasServices and sBTC contracts as parameters. However, the GasServices contract is not used in the our implementation, so basically we can pass the address of contract deployed by Axelar team (e.g. 0xbE406F0189A0B4cf3A05C286473D23791Dd44Cc6 on Sepolia).
4. BurnContract: Deployment of this contract is similar to MintContract.

How do these contracts work together?

Minting flow

1. BTC -> Axelar stuff

2. Relayer listen and handle the ContractCallApproved event from Axelar network. In this step, relayer will generate executeData from batch commands and call execute() function of AxelarGateway contract.

   const executeData = await vxClient.getExecuteDataFromBatchCommands(
     event.args.destinationChain,
     batchedCommandId
   );
   
   logger.info(
     `[handleCosmosToEvmApprovedEvent] BatchCommands: ${JSON.stringify(
       executeData
     )}`
   );
   
   const tx = await evmClient.gatewayExecute(executeData);

3. In this execute() function, the input first will be decoded to data part and proof part. These values then will be validated by the validateProof() function of AxelarAuthWeighted contract.

4. If the proof is valid, the gateway contract will process commands in the data part. In this case, it will call its approveContractCall() function and emit ContractCallApproved event, indicating that the Minting call is approved to be executed.

5. Relayer will listen to this event and call the execute() function of the MintContract contract.

   • The execute() function is actually the execute() function of the AxelarExecutable interface. It first check if the Minting call is approved and then call the _execute() function of MintContract.
   • This _execute() will then call sBTC contract to mint the token.

Burning flow

1. To unbonding Bitcoin transaction, the staker first need to burn their sBTC token on Ethereum network.

2. First, the staker need to approve the BurnContract to burn their sBTC token. This is done by calling the approve() function of the sBTC contract.

   const tx = await sBTC.approve(burnContract.address, amountToBurn);
   await tx.wait();

3. Then, the staker can call the callBurn() function of the BurnContract contract with necessary parameters.

   const txCallBurn = await burnContract.callBurn(
     destinationChain,
     destinationAddress,
     amountToBurn,
     btcPsbtB64
   );
   await txCallBurn.wait();

4. This callBurn() function will then call sBTC contract to burn the token and call the callContract() function of the AxelarGateway contract to emit ContractCall event for relayer to listen and handle.

Contract for GMP

• If you want to create another contract for GMP in Axelar network, you can follow the same pattern as MintContract and BurnContract. The contract need to implement the AxelarExecutable interface with the same constructor.
• If your contract execute logic in the BTC -> EVM direction, write your logic in the _execute() function such as MintContract.
• If your contract execute logic in the EVM -> BTC direction, write your logic in the callContract() function such as BurnContract.
• For more details, please refer to this example.

sBTC Ownership

Currently, the ownership of the sBTC contract is set to the MintContract. This is to ensure that only the MintContract can mint the token. If you want to change the ownership, you can call the transferOwnership() function of the sBTC contract (using the deployer account). Details can be found in the scripts/setOwnership.js.

Axelar Operatorship

The operatorship of the Axelar network is managed by the AxelarAuthWeighted contract. The operator can be added by calling the transferOperatorship() function of this contract. Details can be found in the scripts/transferOperatorShip.js.

Deploy contract batch

To deploy all contract in once time.

node scripts/deployAll.js deploy <target> --network <string> --newSbtc <bool> --newAxelarGateway <bool>

1. target: choice "All, AxelarGateway, MintContract, BurnContract"
2. network: network name < ethereum-sepolia, ethereum-local>
3. --newSbtc: a parameter to specify whether to deploy a new contract sBtc
4. --newAxelarGateway: a parameter to specify whether to deploy a new contract AxelarGateway when deploying Mint/Burn Contract
5. --AxelarGatewayAddress: input AxelarGateway address when newAxelarGateway is false