Tokens (BTC-20)

The BTC-20 token standard on Bitcoin is similar to ERC-20 on Ethereum. It can represent virtually anything in Bitcoin:

  • a cryptocurrency a share in a company voting rights in a DAO a fiat currency like USD an ounce of gold loyalty points and more

​

Write a BTC-20 smart contract

Extending the OpenZeppelin ERC-20 contract, we can create a governance token (BIT) for a hypothetical DEX (Bitswap) on Bitcoin.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
​
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
​
contract Bitswap is ERC20 {
    constructor(uint256 initialSupply) ERC20("Bitswap", "BIT") {
        _mint(msg.sender, initialSupply);
    }
}
​

Clone the smart contract examples

We've prepared a few different examples for you to get started.

git clone https://github.com/bitcoinevm/smart-contract-examples.git

​

Compile the contracts

To compile your contracts, use the built-in hardhat compile task.

cd smart-contract-examples

npm install

npx hardhat compile

Deploy the contracts

Review config file hardhat.config.ts. The network configs should look like this.

networks: {
    mynw: {
      url: "http://localhost:10002",
      accounts: {
        mnemonic: "<your mnemonic with funds>"
      },
      timeout: 100_000,
    },
    blockscoutVerify: {
      blockscoutURL: "http://localhost:4000", // your explorer URL
      ...
    }
  }

Run the deploy scripts using hardhat-deploy.

npx hardhat deploy --tags ERC20

Make sure the accounts in hardhat.config.ts have some BTC.

​

Interact with the contracts

Once the contracts are deployed, you can interact with them. We've prepared a few hardhat tasks to make it easy for you to interact with the contracts.

npx hardhat balanceERC20

npx hardhat transferERC20 --from <your-address> --amount 0.1 --to <your-address>


//// SPDX-License-Identifier: MIT
// Contract by Bitcoin EVM.

pragma solidity ^0.4.23;
contract owned {
    address public owner;
constructor() public {
        owner = msg.sender;
    }
modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }
function transferOwnership(address newOwner) onlyOwner public {
        owner = newOwner;
    }
}
interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }
contract TokenERC20 {
    string public name;
    string public symbol;
    uint8 public decimals = 18;
    uint256 public totalSupply;
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;
    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
    event Burn(address indexed from, uint256 value);

    constructor(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);
        balanceOf[msg.sender] = totalSupply;
        name = tokenName;
        symbol = tokenSymbol;
    }

    function _transfer(address _from, address _to, uint _value) internal {

        require(_to != 0x0);

        require(balanceOf[_from] >= _value);

        require(balanceOf[_to] + _value > balanceOf[_to]);

        uint previousBalances = balanceOf[_from] + balanceOf[_to];

        balanceOf[_from] -= _value;

        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);

        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    function transfer(address _to, uint256 _value) public returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        balanceOf[msg.sender] -= _value;
        totalSupply -= _value;
        emit Burn(msg.sender, _value);
        return true;
    }

    function burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(balanceOf[_from] >= _value);
        require(_value <= allowance[_from][msg.sender]);
        balanceOf[_from] -= _value;
        allowance[_from][msg.sender] -= _value;
        totalSupply -= _value;
        emit Burn(_from, _value);
        return true;
    }
}

contract ERC20Token is owned, TokenERC20 {
uint256 public sellPrice;
    uint256 public buyPrice;
mapping (address => bool) public frozenAccount;

    event FrozenFunds(address target, bool frozen);

    constructor(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) TokenERC20(initialSupply, tokenName, tokenSymbol) public {}

    function _transfer(address _from, address _to, uint _value) internal {
        require (_to != 0x0);
        require (balanceOf[_from] >= _value);
        require (balanceOf[_to] + _value >= balanceOf[_to]);
        require(!frozenAccount[_from]);
        require(!frozenAccount[_to]);
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);
    }

    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        emit Transfer(0, this, mintedAmount);
        emit Transfer(this, target, mintedAmount);
    }

    function freezeAccount(address target, bool freeze) onlyOwner public {
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }

    function setPrices(uint256 newSellPrice, uint256 newBuyPrice) onlyOwner public {
        sellPrice = newSellPrice;
        buyPrice = newBuyPrice;
    }

    function buy() payable public {
        uint amount = msg.value / buyPrice;
        _transfer(this, msg.sender, amount);
    }

    function sell(uint256 amount) public {
        address myAddress = this;
        require(myAddress.balance >= amount * sellPrice);
        _transfer(msg.sender, this, amount);
        msg.sender.transfer(amount * sellPrice);
    }
}

Last updated