//! Implements an example PSBT workflow. //! //! The workflow we simulate is that of a setup using a watch-only online wallet (contains only //! public keys) and a cold-storage signing wallet (contains the private keys). //! //! You can verify the workflow using `bitcoind` and `bitcoin-cli`. //! //! ## Example Setup //! //! 1. Start Bitcoin Core in Regtest mode, for example: //! //! `bitcoind -regtest -server -daemon -fallbackfee=0.0002 -rpcuser=admin -rpcpassword=pass -rpcallowip=127.0.0.1/0 -rpcbind=127.0.0.1 -blockfilterindex=1 -peerblockfilters=1` //! //! 2. Define a shell alias to `bitcoin-cli`, for example: //! //! `alias bt=bitcoin-cli -rpcuser=admin -rpcpassword=pass -rpcport=18443` //! //! 3. Create (or load) a default wallet, for example: //! //! `bt createwallet ` //! //! 4. Mine some blocks, for example: //! //! `bt generatetoaddress 110 $(bt getnewaddress)` //! //! 5. Get the details for a UTXO to fund the PSBT with: //! //! `bt listunspent` //! use std::boxed::Box; use std::collections::BTreeMap; use std::fmt; use std::str::FromStr; use bitcoin::bip32::{ChildNumber, DerivationPath, Fingerprint, IntoDerivationPath, Xpriv, Xpub}; use bitcoin::consensus::encode; use bitcoin::locktime::absolute; use bitcoin::psbt::{self, Input, Psbt, PsbtSighashType}; use bitcoin::secp256k1::{Secp256k1, Signing, Verification}; use bitcoin::{ transaction, Address, Amount, Network, OutPoint, PublicKey, ScriptBuf, Sequence, Transaction, TxIn, TxOut, Witness, }; type Result = std::result::Result; // Get this from the output of `bt dumpwallet `. const EXTENDED_MASTER_PRIVATE_KEY: &str = "tprv8ZgxMBicQKsPeSHZFZWT8zxie2dXWcwemnTkf4grVzMvP2UABUxqbPTCHzZ4ztwhBghpfFw27sJqEgW6y1ZTZcfvCUdtXE1L6qMF7TBdbqQ"; // Set these with valid data from output of step 5 above. Please note, input utxo must be a p2wpkh. const INPUT_UTXO_TXID: &str = "295f06639cde6039bf0c3dbf4827f0e3f2b2c2b476408e2f9af731a8d7a9c7fb"; const INPUT_UTXO_VOUT: u32 = 0; const INPUT_UTXO_SCRIPT_PUBKEY: &str = "00149891eeb8891b3e80a2a1ade180f143add23bf5de"; const INPUT_UTXO_VALUE: &str = "50 BTC"; // Get this from the desciptor, // "wpkh([97f17dca/0'/0'/0']02749483607dafb30c66bd93ece4474be65745ce538c2d70e8e246f17e7a4e0c0c)#m9n56cx0". const INPUT_UTXO_DERIVATION_PATH: &str = "m/0h/0h/0h"; // Grab an address to receive on: `bt generatenewaddress` (obviously contrived but works as an example). const RECEIVE_ADDRESS: &str = "bcrt1qcmnpjjjw78yhyjrxtql6lk7pzpujs3h244p7ae"; // The address to receive the coins we send. // These should be correct if the UTXO above should is for 50 BTC. const OUTPUT_AMOUNT_BTC: &str = "1 BTC"; const CHANGE_AMOUNT_BTC: &str = "48.99999 BTC"; // 1000 sat transaction fee. const NETWORK: Network = Network::Regtest; fn main() -> Result<()> { let secp = Secp256k1::new(); let (offline, fingerprint, account_0_xpub, input_xpub) = ColdStorage::new(&secp, EXTENDED_MASTER_PRIVATE_KEY)?; let online = WatchOnly::new(account_0_xpub, input_xpub, fingerprint); let created = online.create_psbt(&secp)?; let updated = online.update_psbt(created)?; let signed = offline.sign_psbt(&secp, updated)?; let finalized = online.finalize_psbt(signed)?; // You can use `bt sendrawtransaction` to broadcast the extracted transaction. let tx = finalized.extract_tx_unchecked_fee_rate(); tx.verify(|_| Some(previous_output())).expect("failed to verify transaction"); let hex = encode::serialize_hex(&tx); println!("You should now be able to broadcast the following transaction: \n\n{}", hex); Ok(()) } // We cache the pubkeys for convenience because it requires a scep context to convert the private key. /// An example of an offline signer i.e., a cold-storage device. struct ColdStorage { /// The master extended private key. master_xpriv: Xpriv, /// The master extended public key. master_xpub: Xpub, } /// The data exported from an offline wallet to enable creation of a watch-only online wallet. /// (wallet, fingerprint, account_0_xpub, input_utxo_xpub) type ExportData = (ColdStorage, Fingerprint, Xpub, Xpub); impl ColdStorage { /// Constructs a new `ColdStorage` signer. /// /// # Returns /// /// The newly created signer along with the data needed to configure a watch-only wallet. fn new(secp: &Secp256k1, xpriv: &str) -> Result { let master_xpriv = Xpriv::from_str(xpriv)?; let master_xpub = Xpub::from_priv(secp, &master_xpriv); // Hardened children require secret data to derive. let path = "m/84h/0h/0h".into_derivation_path()?; let account_0_xpriv = master_xpriv.derive_priv(secp, &path)?; let account_0_xpub = Xpub::from_priv(secp, &account_0_xpriv); let path = INPUT_UTXO_DERIVATION_PATH.into_derivation_path()?; let input_xpriv = master_xpriv.derive_priv(secp, &path)?; let input_xpub = Xpub::from_priv(secp, &input_xpriv); let wallet = ColdStorage { master_xpriv, master_xpub }; let fingerprint = wallet.master_fingerprint(); Ok((wallet, fingerprint, account_0_xpub, input_xpub)) } /// Returns the fingerprint for the master extended public key. fn master_fingerprint(&self) -> Fingerprint { self.master_xpub.fingerprint() } /// Signs `psbt` with this signer. fn sign_psbt(&self, secp: &Secp256k1, mut psbt: Psbt) -> Result { match psbt.sign(&self.master_xpriv, secp) { Ok(keys) => assert_eq!(keys.len(), 1), Err((_, e)) => { let e = e.get(&0).expect("at least one error"); return Err(e.clone().into()); } }; Ok(psbt) } } /// An example of an watch-only online wallet. struct WatchOnly { /// The xpub for account 0 derived from derivation path "m/84h/0h/0h". account_0_xpub: Xpub, /// The xpub derived from `INPUT_UTXO_DERIVATION_PATH`. input_xpub: Xpub, /// The master extended pubkey fingerprint. master_fingerprint: Fingerprint, } impl WatchOnly { /// Constructs a new watch-only wallet. /// /// A watch-only wallet would typically be online and connected to the Bitcoin network. We /// 'import' into the wallet the `account_0_xpub` and `master_fingerprint`. /// /// The reason for importing the `input_xpub` is so one can use bitcoind to grab a valid input /// to verify the workflow presented in this file. fn new(account_0_xpub: Xpub, input_xpub: Xpub, master_fingerprint: Fingerprint) -> Self { WatchOnly { account_0_xpub, input_xpub, master_fingerprint } } /// Creates the PSBT, in BIP174 parlance this is the 'Creater'. fn create_psbt(&self, secp: &Secp256k1) -> Result { let to_address = Address::from_str(RECEIVE_ADDRESS)?.require_network(Network::Regtest)?; let to_amount = Amount::from_str(OUTPUT_AMOUNT_BTC)?; let (_, change_address, _) = self.change_address(secp)?; let change_amount = Amount::from_str(CHANGE_AMOUNT_BTC)?; let tx = Transaction { version: transaction::Version::TWO, lock_time: absolute::LockTime::ZERO, input: vec![TxIn { previous_output: OutPoint { txid: INPUT_UTXO_TXID.parse()?, vout: INPUT_UTXO_VOUT }, script_sig: ScriptBuf::new(), sequence: Sequence::MAX, // Disable LockTime and RBF. witness: Witness::default(), }], output: vec![ TxOut { value: to_amount, script_pubkey: to_address.script_pubkey() }, TxOut { value: change_amount, script_pubkey: change_address.script_pubkey() }, ], }; let psbt = Psbt::from_unsigned_tx(tx)?; Ok(psbt) } /// Updates the PSBT, in BIP174 parlance this is the 'Updater'. fn update_psbt(&self, mut psbt: Psbt) -> Result { let mut input = Input { witness_utxo: Some(previous_output()), ..Default::default() }; let pk = self.input_xpub.to_pub(); let wpkh = pk.wpubkey_hash().expect("a compressed pubkey"); let redeem_script = ScriptBuf::new_p2wpkh(&wpkh); input.redeem_script = Some(redeem_script); let fingerprint = self.master_fingerprint; let path = input_derivation_path()?; let mut map = BTreeMap::new(); map.insert(pk.inner, (fingerprint, path)); input.bip32_derivation = map; let ty = PsbtSighashType::from_str("SIGHASH_ALL")?; input.sighash_type = Some(ty); psbt.inputs = vec![input]; Ok(psbt) } /// Finalizes the PSBT, in BIP174 parlance this is the 'Finalizer'. /// This is just an example. For a production-ready PSBT Finalizer, use [rust-miniscript](https://docs.rs/miniscript/latest/miniscript/psbt/trait.PsbtExt.html#tymethod.finalize) fn finalize_psbt(&self, mut psbt: Psbt) -> Result { if psbt.inputs.is_empty() { return Err(psbt::SignError::MissingInputUtxo.into()); } let sigs: Vec<_> = psbt.inputs[0].partial_sigs.values().collect(); let mut script_witness: Witness = Witness::new(); script_witness.push(&sigs[0].to_vec()); script_witness.push(self.input_xpub.to_pub().to_bytes()); psbt.inputs[0].final_script_witness = Some(script_witness); // Clear all the data fields as per the spec. psbt.inputs[0].partial_sigs = BTreeMap::new(); psbt.inputs[0].sighash_type = None; psbt.inputs[0].redeem_script = None; psbt.inputs[0].witness_script = None; psbt.inputs[0].bip32_derivation = BTreeMap::new(); Ok(psbt) } /// Returns data for the first change address (standard BIP84 derivation path /// "m/84h/0h/0h/1/0"). A real wallet would have access to the chain so could determine if an /// address has been used or not. We ignore this detail and just re-use the first change address /// without loss of generality. fn change_address( &self, secp: &Secp256k1, ) -> Result<(PublicKey, Address, DerivationPath)> { let path = [ChildNumber::from_normal_idx(1)?, ChildNumber::from_normal_idx(0)?]; let derived = self.account_0_xpub.derive_pub(secp, &path)?; let pk = derived.to_pub(); let addr = Address::p2wpkh(&pk, NETWORK)?; let path = path.into_derivation_path()?; Ok((pk, addr, path)) } } fn input_derivation_path() -> Result { let path = INPUT_UTXO_DERIVATION_PATH.into_derivation_path()?; Ok(path) } fn previous_output() -> TxOut { let script_pubkey = ScriptBuf::from_hex(INPUT_UTXO_SCRIPT_PUBKEY) .expect("failed to parse input utxo scriptPubkey"); let amount = Amount::from_str(INPUT_UTXO_VALUE).expect("failed to parse input utxo value"); TxOut { value: amount, script_pubkey } } struct Error(Box); impl From for Error { fn from(e: T) -> Self { Error(Box::new(e)) } } impl fmt::Debug for Error { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { fmt::Debug::fmt(&self.0, f) } }