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btc-outbound.md

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Bitcoin - Outbound (WBTC ⇒ BTC)

Basic Steps

  • Get outbound fee
  • Send lock tx on Wanchain with outbound fee
  • Wait for storeman response on Wanchain
  • Get txid and lockTime from response
  • Send redeem tx on Bitcoin

Required and optional fields

Lock fields

  • to - the redeeming Bitcoin address
  • from - the sending Wanchain address
  • value - the value to be transferred (in satoshis)
  • storeman - the storeman (wan/btc) accounts to use
  • redeemKey - the tx redeem key, including x and xHash

Redeem fields

  • to - the redeeming Bitcoin address (legacy type only)
  • payTo - the Bitcoin address where to send funds (optional, defaults to to; type legacy, P2SH, or bech32)
  • value - the value to be transferred (in satoshis, excluding the mining fee)
  • storeman - the storeman btc account
  • redeemKey - the tx redeem key, including x and xHash
  • txid - the txid of the tx that funds the P2SH lock address, as reported by the storeman lock confirmation
  • lockTime - the lockTime of the P2SH lock address, as reported by the storeman lock confirmation
  • redeemScript - the redeemScript of the P2SH lock address
  • publicKey - the public key of the redeeming to address
  • sigHash - the signature hash of the redeeming tx, signed externally with redeeming private key
  • wif - use in place of publicKey and sigHash; the private key of the to address, in WIF format

Revoke fields

  • from - the sending Wanchain address
  • redeemKey - the tx redeem key, including x and xHash

Using Wanx

For outbound bitcoin transactions, the lock process is all on Wanchain, and the redeem process is just on Bitcoin.

Lock on Wanchain

Simple Usage: if the specified Wanchain account is open, then you can do the whole crosschain transaction all in one call. You will want to set up event handlers to watch for progress.

cctx.lock(opts);

cctx.on('info', info => {
...
cctx.on('error', err => {
...
cctx.on('complete', res => {
...

Advanced Usage: if you need to handle each step separately, like if some steps need to happen on the client and others on the server, or if you need to sign the transactions manually, you can use WanX to handle each step of the crosschain transaction.

// fine grain handling
Promise.resolve([]).then(() => {

  return cctx.getOutboundFee(opts);

}).then(fee => {

  opts.outboundFee = fee;

  const lockTx = cctx.buildLockTx(opts);
  return webwan.eth.sendTransaction(lockTx);

}).then(receipt => {

  return cctx.listenLock(opts);

}).then(log => {
...

Redeem bitcoin

Once the storeman responds with the lock confirmation, you can then redeem the bitcoin from the lock address. First, you will need to get the lockTime from the storeman lock confirmation event. Then with the lockTime, rebuild the P2SH lock address to derive its redeemScript.

Rebuild P2SH lock address

opts.lockTime = lockTime;

// reconstruct P2SH
const contract = cctx.buildHashTimeLockContract(opts);

opts.redeemScript = contract.redeemScript;

With the lockTime and redeemScript added to opts, build the redeem transaction either by passing in the redeemer private key to the buildRedeemTxFromWif method, or by using hashForRedeemSig to get the hash for signature, then signing it and passing it along with the public key of the redeemer address to the buildRedeemTx method.

Build redeem using WIF

opts.wif = 'cNggJXP2mMNSHA1r9CRd1sv65uykZNyeH8wkH3ZPZVUL1nLfTxRM';

// build redeem tx
const signedTx = cctx.buildRedeemTxFromWif(opts);

Build redeem using sigHash

const bitcoin = require('bitcoinjs-lib');

...

const publicKey = '03e55a948b017ad25994cbe3e10842bffc8835054f56528fe2ed32b9e6ec853e4c';

// get hash for signature
const hashForSignature = cctx.hashForRedeemSig(opts);

// sign hash
const keyPair = bitcoin.ECPair.fromWIF(wif, bitcoin.networks.testnet);
const sigHash = keyPair.sign(new Buffer.from(hashForSignature, 'hex'));

// build redeem tx
const signedTx = cctx.buildRedeemTx(Object.assign({}, opts, { sigHash, publicKey }));

Both the buildRedeemTx and buildRedeemTxFromWif methods return the signed transaction in hex format, ready to be sent on to the network through a Bitcoin node.