Adding Plan Example for taproot based on asset planning

Signed-off-by: Harshil Jani <harshiljani2002@gmail.com>

Cargo.toml

@@ -65,3 +65,7 @@ required-features = ["std", "base64"]
 [workspace]
 members = ["bitcoind-tests", "fuzz"]
 exclude = ["embedded"]
+
+[[example]]
+name = "plan_spend"
+required-features = ["std", "base64"]

examples/plan_spend.rs

@@ -0,0 +1,258 @@
+use std::collections::BTreeMap;
+use std::str::FromStr;
+
+use bitcoin::absolute::Height;
+use bitcoin::blockdata::locktime::absolute;
+use bitcoin::key::TapTweak;
+use bitcoin::psbt::{self, Psbt};
+use bitcoin::sighash::SighashCache;
+use bitcoin::{taproot, PrivateKey, ScriptBuf};
+use miniscript::bitcoin::consensus::encode::deserialize;
+use miniscript::bitcoin::hashes::hex::FromHex;
+use miniscript::bitcoin::{
+    self, base64, secp256k1, Address, Network, OutPoint, Sequence, Transaction, TxIn, TxOut,
+};
+use miniscript::psbt::{PsbtExt, PsbtInputExt};
+use miniscript::{Descriptor, DescriptorPublicKey};
+use secp256k1::Secp256k1;
+
+fn main() {
+    // Defining the descriptor keys required.
+    let secp256k1 = secp256k1::Secp256k1::new();
+    let keys = vec![
+        "036a7ae441409bd40af1b8efba7dbd34b822b9a72566eff10b889b8de13659e343",
+        "03b6c8a1a901edf3c5f1cb0e3ffe1f20393435a5d467f435e2858c9ab43d3ca78c",
+        "03500a2b48b0f66c8183cc0d6645ab21cc19c7fad8a33ff04d41c3ece54b0bc1c5",
+        "033ad2d191da4f39512adbaac320cae1f12f298386a4e9d43fd98dec7cf5db2ac9",
+        "023fc33527afab09fa97135f2180bcd22ce637b1d2fbcb2db748b1f2c33f45b2b4",
+    ];
+
+    // The taproot descriptor combines different spending paths and conditions, allowing the funds to be spent using
+    // different methods depending on the desired conditions.
+
+    // tr({A},{{pkh({B}),{{multi_a(1,{C},{D}),and_v(v:pk({E}),after(10))}}}}) represents a taproot spending policy.
+    // Let's break it down:
+    //
+    // * Key Spend Path
+    // {A} represents the public key for the taproot key spending path.
+    //
+    // * Script Spend Paths
+    // {B} represents the public key for the pay-to-pubkey-hash (P2PKH) spending path.
+    // The multi_a(1,{C},{D}) construct represents a 1-of-2 multi-signature script condition.
+    // It requires at least one signature from {C} and {D} to spend funds using the script spend path.
+    // The and_v(v:pk({E}),after(10)) construct represents a combination of a P2PK script condition and a time lock.
+    // It requires a valid signature from {E} and enforces a time lock of 10 blocks on spending funds.
+
+    // By constructing transactions using this taproot descriptor and signing them appropriately,
+    // you can create flexible spending policies that enable different spending paths and conditions depending on the
+    // transaction's inputs and outputs.
+    let s = format!(
+        "tr({},{{pkh({}),{{multi_a(1,{},{}),and_v(v:pk({}),after(10))}}}})",
+        keys[0], keys[1], keys[2], keys[3], keys[4]
+    );
+
+    let bridge_descriptor = Descriptor::from_str(&s).expect("parse descriptor string");
+    assert!(bridge_descriptor.sanity_check().is_ok());
+
+    println!(
+        "Bridge pubkey script: {}",
+        bridge_descriptor.script_pubkey()
+    );
+    println!(
+        "Bridge address: {}",
+        bridge_descriptor.address(Network::Regtest).unwrap()
+    );
+
+    let master_private_key_str = "KxQqtbUnMugSEbKHG3saknvVYux1cgFjFqWzMfwnFhLm8QrGq26v";
+    let master_private_key =
+        PrivateKey::from_str(master_private_key_str).expect("Can't create private key");
+    println!(
+        "Master public key: {}",
+        master_private_key.public_key(&secp256k1)
+    );
+
+    let backup1_private_key_str = "Kwb9oFfPNt6D3Fa9DCF5emRvLyJ3UUvCHnVxp4xf7bWDxWmeVdeH";
+    let backup1_private =
+        PrivateKey::from_str(backup1_private_key_str).expect("Can't create private key");
+
+    println!(
+        "Backup1 public key: {}",
+        backup1_private.public_key(&secp256k1)
+    );
+
+    let backup2_private_key_str = "cPJFWUKk8sdL7pcDKrmNiWUyqgovimmhaaZ8WwsByDaJ45qLREkh";
+    let backup2_private =
+        PrivateKey::from_str(backup2_private_key_str).expect("Can't create private key");
+
+    println!(
+        "Backup2 public key: {}",
+        backup2_private.public_key(&secp256k1)
+    );
+
+    let backup3_private_key_str = "cT5cH9UVm81W5QAf5KABXb23RKNSMbMzMx85y6R2mF42L94YwKX6";
+    let _backup3_private =
+        PrivateKey::from_str(backup3_private_key_str).expect("Can't create private key");
+
+    println!(
+        "Backup3 public key: {}",
+        _backup3_private.public_key(&secp256k1)
+    );
+
+    // Create a spending transaction
+    let spend_tx = Transaction {
+        version: 2,
+        lock_time: absolute::LockTime::Blocks(Height::ZERO),
+        input: vec![],
+        output: vec![],
+    };
+
+    let hex_tx = "020000000001018ff27041f3d738f5f84fd5ee62f1c5b36afebfb15f6da0c9d1382ddd0eaaa23c0000000000feffffff02b3884703010000001600142ca3b4e53f17991582d47b15a053b3201891df5200e1f5050000000022512061763f4288d086c0347c4e3c387ce22ab9372cecada6c326e77efd57e9a5ea460247304402207b820860a9d425833f729775880b0ed59dd12b64b9a3d1ab677e27e4d6b370700220576003163f8420fe0b9dc8df726cff22cbc191104a2d4ae4f9dfedb087fcec72012103817e1da42a7701df4db94db8576f0e3605f3ab3701608b7e56f92321e4d8999100000000";
+    let depo_tx: Transaction = deserialize(&Vec::<u8>::from_hex(hex_tx).unwrap()).unwrap();
+
+    let receiver = Address::from_str("bcrt1qsdks5za4t6sevaph6tz9ddfjzvhkdkxe9tfrcy").unwrap();
+
+    let amount = 100000000;
+
+    let (outpoint, witness_utxo) = get_vout(&depo_tx, bridge_descriptor.script_pubkey());
+
+    let all_assets = Descriptor::<DescriptorPublicKey>::from_str(&s)
+        .unwrap()
+        .get_all_assets()
+        .unwrap();
+
+    for asset in all_assets {
+        // Creating a PSBT Object
+        let mut psbt = Psbt {
+            unsigned_tx: spend_tx.clone(),
+            unknown: BTreeMap::new(),
+            proprietary: BTreeMap::new(),
+            xpub: BTreeMap::new(),
+            version: 0,
+            inputs: vec![],
+            outputs: vec![],
+        };
+
+        // Defining the Transaction Input
+        let mut txin = TxIn::default();
+        txin.previous_output = outpoint;
+        txin.sequence = Sequence::from_height(26); //Sequence::MAX; //
+        psbt.unsigned_tx.input.push(txin);
+
+        // Defining the Transaction Output
+        psbt.unsigned_tx.output.push(TxOut {
+            script_pubkey: receiver.payload.script_pubkey(),
+            value: amount / 5 - 500,
+        });
+
+        psbt.unsigned_tx.output.push(TxOut {
+            script_pubkey: bridge_descriptor.script_pubkey(),
+            value: amount * 4 / 5,
+        });
+
+        // Consider that out of all the keys required to sign the descriptor spend path we only have some handful of assets.
+        // We can plan the PSBT with only few assets(keys or hashes) if that are enough for satisfying any policy.
+        //
+        // Here for example assume that we only have two keys available.
+        // Key A and Key B (as seen from the descriptor above)
+        // We have to add the keys to `Asset` and then obtain plan with only available signatures if  the descriptor can be satisfied.
+
+        // Obtain the Plan based on available Assets
+        let plan = bridge_descriptor.clone().plan(&asset).unwrap();
+
+        // Creating PSBT Input
+        let mut input = psbt::Input::default();
+        plan.update_psbt_input(&mut input);
+
+        // Update the PSBT input from the result which we have obtained from the Plan.
+        input
+            .update_with_descriptor_unchecked(&bridge_descriptor)
+            .unwrap();
+        input.witness_utxo = Some(witness_utxo.clone());
+
+        // Push the PSBT Input and declare an PSBT Output Structure
+        psbt.inputs.push(input);
+        psbt.outputs.push(psbt::Output::default());
+
+        // Use private keys to sign
+        let key_a = master_private_key.inner;
+        let key_b = backup1_private.inner;
+
+        // Taproot script can be signed when we have either Key spend or Script spend or both.
+        // Here you can try to verify by commenting one of the spend path or try signing with both.
+        sign_taproot_psbt(&key_a, &mut psbt, &secp256k1); // Key Spend - With Key A
+        sign_taproot_psbt(&key_b, &mut psbt, &secp256k1); // Script Spend - With Key B
+
+        // Serializing and finalizing the PSBT Transaction
+        let serialized = psbt.serialize();
+        println!("{}", base64::encode(&serialized));
+        psbt.finalize_mut(&secp256k1).unwrap();
+
+        let tx = psbt.extract_tx();
+        println!("{}", bitcoin::consensus::encode::serialize_hex(&tx));
+    }
+}
+
+// Siging the Taproot PSBT Transaction
+fn sign_taproot_psbt(
+    secret_key: &secp256k1::SecretKey,
+    psbt: &mut psbt::Psbt,
+    secp256k1: &Secp256k1<secp256k1::All>,
+) {
+    // Creating signing entitites required
+    let hash_ty = bitcoin::sighash::TapSighashType::Default;
+    let mut sighash_cache = SighashCache::new(&psbt.unsigned_tx);
+
+    // Defining Keypair for given private key
+    let keypair = secp256k1::KeyPair::from_seckey_slice(&secp256k1, secret_key.as_ref()).unwrap();
+
+    // Checking if leaf hash exist or not.
+    // For Key Spend -> Leaf Hash is None
+    // For Script Spend -> Leaf Hash is Some(_)
+    // Convert this leaf_hash tree to a full map.
+    let (leaf_hashes, (_, _)) = &psbt.inputs[0].tap_key_origins[&keypair.x_only_public_key().0];
+    let leaf_hash = if !leaf_hashes.is_empty() {
+        Some(leaf_hashes[0])
+    } else {
+        None
+    };
+
+    let keypair = match leaf_hash {
+        None => keypair
+            .tap_tweak(&secp256k1, psbt.inputs[0].tap_merkle_root)
+            .to_inner(), // tweak for key spend
+        Some(_) => keypair, // no tweak for script spend
+    };
+
+    // Construct the message to input for schnorr signature
+    let msg = psbt
+        .sighash_msg(0, &mut sighash_cache, leaf_hash)
+        .unwrap()
+        .to_secp_msg();
+    let sig = secp256k1.sign_schnorr(&msg, &keypair);
+    let (pk, _parity) = keypair.x_only_public_key();
+    assert!(secp256k1.verify_schnorr(&sig, &msg, &pk).is_ok());
+
+    // Create final signature with corresponding hash type
+    let final_signature1 = taproot::Signature { hash_ty, sig };
+
+    if let Some(lh) = leaf_hash {
+        // Script Spend
+        psbt.inputs[0]
+            .tap_script_sigs
+            .insert((pk, lh), final_signature1);
+    } else {
+        // Key Spend
+        psbt.inputs[0].tap_key_sig = Some(final_signature1);
+        println!("{:#?}", psbt);
+    }
+}
+
+// Find the Outpoint by spk
+fn get_vout(tx: &Transaction, spk: ScriptBuf) -> (OutPoint, TxOut) {
+    for (i, txout) in tx.clone().output.into_iter().enumerate() {
+        if spk == txout.script_pubkey {
+            return (OutPoint::new(tx.txid(), i as u32), txout);
+        }
+    }
+    panic!("Only call get vout on functions which have the expected outpoint");
+}