Multi-Blockchain Wallet in Python

Send transcations with ETH and BTC

Multi-Blockchain Wallet in Python

Background

Your new startup is focusing on building a portfolio management system that supports not only traditional assets like gold, silver, stocks, etc, but crypto-assets as well! The problem is, there are so many coins out there! It's a good thing you understand how HD wallets work, since you'll need to build out a system that can create them.

You're in a race to get to the market. There aren't as many tools available in Python for this sort of thing, yet. Thankfully, you've found a command line tool, hd-wallet-derive that supports not only BIP32, BIP39, and BIP44, but also supports non-standard derivation paths for the most popular wallets out there today! However, you need to integrate the script into your backend with your dear old friend, Python.

Once you've integrated this "universal" wallet, you can begin to manage billions of addresses across 300+ coins, giving you a serious edge against the competition.

In this assignment, however, you will only need to get 2 coins working: Ethereum and Bitcoin Testnet. Ethereum keys are the same format on any network, so the Ethereum keys should work with your custom networks or testnets.

Instructions

1. Generate a Mnemonic

• Generate a new 12 word mnemonic using hd-wallet-derive or by using this tool.

• Set this mnemonic as an environment variable by storing it a an .env file and importing it into your wallet.py.

2. Derive the wallet keys

• Create a function called derive_wallets that does the following:

  • Use the subprocess library to create a shell command that calls the ./derive script from Python. Make sure to properly wait for the process. Windows Users may need to prepend the php command in front of ./derive like so: php ./derive.

  • The following flags must be passed into the shell command as variables:

    • Mnemonic (--mnemonic) must be set from an environment variable, or default to a test mnemonic
    • Coin (--coin)
    • Numderive (--numderive) to set number of child keys generated
    • Format (--format=json) to parse the output into a JSON object using json.loads(output)

• Create a dictionary object called coins that uses the derive_wallets function to derive ETH and BTCTEST wallets.

• When done properly, the final object should look something like this (there are only 3 children each in this image):

  

• You should now be able to select child accounts (and thus, private keys) by accessing items in the coins dictionary like so: coins[COINTYPE][INDEX]['privkey'].

3. Linking the transaction signing libraries

• Use bit and web3.py to leverage the keys stored in the coins object by creating three more functions:

  • priv_key_to_account:

    • This function will convert the privkey string in a child key to an account object that bit or web3.py can use to transact.

    • This function needs the following parameters:

      • coin -- the coin type (defined in constants.py).
      • priv_key -- the privkey string will be passed through here.

    • You will need to check the coin type, then return one of the following functions based on the library:

      • For ETH, return Account.privateKeyToAccount(priv_key)
        • This function returns an account object from the private key string. You can read more about this object here.
      • For BTCTEST, return PrivateKeyTestnet(priv_key)
        • This is a function from the bit libarary that converts the private key string into a WIF (Wallet Import Format) object. WIF is a special format bitcoin uses to designate the types of keys it generates.
        • You can read more about this function here.

  • create_tx:

    • This function will create the raw, unsigned transaction that contains all metadata needed to transact.

    • This function needs the following parameters:

      • coin -- the coin type (defined in constants.py).
      • account -- the account object from priv_key_to_account.
      • to -- the recipient address.
      • amount -- the amount of the coin to send.

    • You will need to check the coin type, then return one of the following functions based on the library:

      • For ETH, return an object containing to, from, value, gas, gasPrice, nonce, and chainID. Make sure to calculate all of these values properly using web3.py!
      • For BTCTEST, return PrivateKeyTestnet.prepare_transaction(account.address, [(to, amount, BTC)])

• send_tx:

  • This function will call create_tx, sign the transaction, then send it to the designated network.

  • This function needs the following parameters:

    • coin -- the coin type (defined in constants.py).
    • account -- the account object from priv_key_to_account.
    • to -- the recipient address.
    • amount -- the amount of the coin to send.

  • You may notice these are the exact same parameters as create_tx. send_tx will call create_tx, so it needs all of this information available.

  • You will need to check the coin, then create a raw_tx object by calling create_tx. Then, you will need to sign the raw_tx using bit or web3.py (hint: the account objects have a sign transaction function within).

  • Once you've signed the transaction, you will need to send it to the designated blockchain network.

    • For ETH, return w3.eth.sendRawTransaction(signed.rawTransaction)
    • For BTCTEST, return NetworkAPI.broadcast_tx_testnet(signed)

4. Send some transactions!

• Now, you should be able to fund these wallets using testnet faucets.

• Open up a new terminal window inside of wallet.

• Then run the command python to open the Python shell.

• Within the Python shell, run the command from wallet import *. This will allow you to access the functions in wallet.py interactively.

• You'll need to set the account with priv_key_to_account and use send_tx to send transactions.

  • Bitcoin Testnet transaction

    • Fund a BTCTEST address using this testnet faucet.

    • Use a block explorer to watch transactions on the address.

    • Send a transaction to another testnet address (either one of your own, or the faucet's).

    • Screenshot the confirmation of the transaction like so:

      

  • Local PoA Ethereum transaction

    • Add one of the ETH addresses to the pre-allocated accounts in your networkname.json.

    • Delete the geth folder in each node, then re-initialize using geth --datadir nodeX init networkname.json. This will create a new chain, and will pre-fund the new account.

    • Add the following middleware to web3.py to support the PoA algorithm:

      from web3.middleware import geth_poa_middleware
      
      w3.middleware_onion.inject(geth_poa_middleware, layer=0)
      

    • Due to a bug in web3.py, you will need to send a transaction or two with MyCrypto first, since the w3.eth.generateGasPrice() function does not work with an empty chain. You can use one of the ETH address privkey, or one of the node keystore files.

    • Send a transaction from the pre-funded address within the wallet to another, then copy the txid into MyCrypto's TX Status, and screenshot the successful transaction like so: