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Bitcoin Integration

The Wanchain cross-chain feature currently includes mainnet and testnet connections with the Bitcoin network. This means that users can use the Wanchain multi-party computing Storeman solution to convert BTC coin on Bitcoin to wBTC (Wanchain BTC token) on the Wanchain network, as well as convert the Wanchain token back to native BTC.

Inbound Transactions

Bitcoin Inbound

Steps for Inbound Bitcoin Cross-chain Transaction

  1. Make a Bitcoin transaction that locks funds in a user-generated timelock P2SH address with a specific redeemScript.
  2. Make a contract call on Wanchain to announce the locked funds.
  3. Wait for a followup contract call on Wanchain from the Storeman group that confirms the lock.
  4. Make a smart contract call on Wanchain to redeem the token.
  5. Wait for a followup contract call on Wanchain from the Storeman group that finalizes the transfer.

Whereas for inbound Ethereum transactions the first step is a single lock call to the smart contract, for inbound Bitcoin it involves 2 steps: one to lock the bitcoin in a timelock P2SH address, and one to request to the Storeman group to initiate the cross-chain transaction using the given funded P2SH address. When the Storeman group sees the lock method called on the Wanchain contract, the Storeman group continues by confirming that the P2SH was generated with the correct P2SH opcodes, and thus has a valid redeemScript. If the address is valid and once the funding transaction has enough confirmations, the Storeman group proceeds by making a followup call on the Wanchain smart contract, which locks the Wanchain token and announces that the token is ready to be redeemed.

Like the Ethereum integration, the smart contracts for the Bitcoin integration enforce that the funds are redeemed within a given time period. In the case of Bitcoin, if the the funds are locked but the redeemer does not redeem the token within 36 hours, then the transaction will move to a “Revoked” state. If that happens, the redeemer will no longer be able to redeem the token, and the sender will have to make a Revoke call to get the locked BTC back.

Outbound Transactions

The steps for outbound transactions are similar to the steps for inbound transactions, though with a few minor differences.

Bitcoin Outbound

Steps for Outbound Bitcoin Cross-chain Transaction

  1. Make a transaction on Wanchain that locks the tokens and that includes the outbound fee in WAN.
  2. Wait for a followup contract call on Bitcoin from the Storeman group that confirms the lock, and that announces the P2SH address where the funds are locked, as well as the id of the transaction that funded the address.
  3. Redeem the BTC from the P2SH address, signing the transaction with the pubkey of the address provided in the initial lock call.
  4. Wait for a followup contract call on Wanchain from the Storeman group that finalizes the transfer.

Like with inbound transactions, if the outbound redeemer does not redeem within the time of the timelock defined in the P2SH address, then the BTC will no longer be redeemable. The Storeman group will reclaim the BTC and the transaction will go into a “Revoked” state. In that case the Revoke call must be made by the sender to get the locked token back.

Connecting to Bitcoin

In the following examples we will use wanx to make cross-chain transactions, which requires that we have access to a Bitcoin full node with RPC and transaction indexing enabled. If you not have access to a Bitcoin node already, follow the steps below to get one set up. If you do already have a Bitcoin node, just make sure it is configured with the all the items in the example bitcoin.conf file shown below.

Install bitcoind

Of course there are many ways to obtain the bitcoind binary. The two options show below are a just couple of the easier ways to install bitcoin, but as always, use your own discretion when deciding where to get your binaries!

Option 1 - Install Bitcoin Core

On Mac, installing the Bitcoin Core package is the simplest way to get the bitcoind binary.

Option 2 - Install bitcoind from ppa

On Ubuntu, you can install bitcoind easily from the ppa.

$ sudo apt-add-repository ppa:bitcoin/bitcoin
$ sudo apt-get update
$ sudo apt-get install bitcoind

Configure node settings

Update the bitcoin config file (~/.bitcoin/bitcoin.conf) and add the required settings to allow RPC connections to the node. Use at least the following config settings.

bitcoin.conf

server=1
rpcuser=myuser
rpcpassword=mypassword
txindex=1

If you want to be able to connect to the bitcoin node from another machine, also set the rpcallowip option. Though remember, if you decide to open up the node to the outside, make sure you protect it somehow. You do not want anybody but yourself to be able to RPC connect to the node!

rpcallowip=192.168.0.0/24

Start bitcoind

Now, start the bitcoind daemon in testnet mode.

$ bitcoind -testnet -daemon

After a while test that you can connect to the Bitcoin node from the command line using bitcoin-cli. The initial sync may take several hours, but you should get results from the getbestblockhash command once the initial sync begins.

$ bitcoin-cli -testnet getbestblockhash