Revoke a Bitcoin Inbound Transaction

If the locked funds are not redeemed by a certain amount of time, then the cross-chain transaction changes to a state of Revoked within the smart contracts. Once it changes to Revoked, the funds can no longer be redeemed by the receiver, but instead must be revoked by the sender.

The amount of time before the cross-chain transaction expires is defined by the cross-chain smart contracts. For Bitcoin it is 72 hours on mainnet and 8 hours on testnet, while for Ethereum it is 8 hours on mainnet and 4 hours on testnet.

Unlike with inbound Ethereum transactions, inbound Bitcoin transactions are revoked not by calling a smart contract, but instead by just spending the bitcoin and sending them to an address that you fully own. The timelock for the Bitcoin lock address, the user generated P2SH address, expires after a certain period, after which the cross-chain transaction will be Revoked and you will be able to spend from the lock address.

Thus, to revoke the transaction we just need to build and send a Bitcoin transaction.

Let’s start by making a new script file for the revoke.

$ vi btc2wbtc-revoke.js

The top portion of the script can be copied from the btc2wbtc.js script. The only things we need to do are:

1. Add in the redeemKey of the expired cross-chain transaction, instead of creating a new redeemKey.
2. Add the txid of the Bitcoin transaction that funded the lock address.
3. Add the WIF of the revoker address.
4. Change the chain of promises so that it just calls the revoke function.

First, let’s make sure to add in the redeemKey generated by the expired inbound transaction, as well as the lockTime, txid, and wif.

const opts = {
  ...
  redeemKey: {
    x: '1327484f41d1990247f5b7e180d0fe4f77e10e1fd414b4e871155b0aa30e44bc',
    xHash: 'd577db3fb3d8718648b4809938f72452c3b7f6613ac1f9159b06b7535b0197b8'
  },

  // Add lockTime used for P2SH address, and txid that funded it
  lockTime: 1542322930,
  txid: '34cbc29ec4edde4415260800561cb318b883b98629881a7d75ed85aa6eb41b03',

  // private key of from address
  wif: 'cNggJXP2mMNSHA1r9CRd1sv65uykZNyeH8wkH3ZPZVUL1nLfTxRM',
};

Finally, we need to specify the amount of miner fee we want to pay for our revoke transaction.

// Total miner fee for revoke (in satoshis)
const minerFee = '600';

Now we can set up the revoke call.

Promise.resolve([])
  .then(sendRevoke)
  .catch(err => {
    console.log('Error:', err);
  });

Finally, we just need to define the sendRevoke function.

function sendRevoke() {

  console.log('Starting btc inbound revoke', opts);

  // Build the contract to get the redeemScript
  const contract = cctx.buildHashTimeLockContract(opts);

  console.log('P2SH contract', contract);

  opts.redeemScript = contract.redeemScript;

  // Subtract miner fee
  const redeemValue = (new BigNumber(opts.value)).minus(minerFee).toString();

  // Get signed revoke tx
  const signedTx = cctx.buildRevokeTxFromWif(
    Object.assign({}, opts, {
      value: redeemValue,
    }),
  );

  console.log('Signed revoke tx:', signedTx);

  // Send the revoke tx to the network
  return utils.sendRawBtcTx(bitcoinRpc, signedTx);
}

In this sendRevoke function, basically two things happen. First, the Bitcoin P2SH address is reconstructed using the buildHashTimeLockContract method, so that the redeemScript can be captured and added to the transaction opts. Second, the revoke transaction is constructed using the buildRevokeTxFromWif method. The miner fee of 600 satoshis is subtracted from the previously defined value before being passed to the buildRevokeTxFromWif method.

Go ahead and run the script.

$ node btc2wbtc-revoke.js

You should just see some output once the revoke call confirms. If you see an error, it is more than likely due to one of two following problems.

1. You did not correctly set the redeemKey, lockTime, txid, or wif in the transaction opts.
2. The timelock has not yet expired.

Now that we have successfully sent and revoked a inbound Bitcoin cross-chain transaction, we are ready to move on to discussing outbound Bitcoin cross-chain transactions.