Updating psbt_sign_finalize example with planning module

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

Author: Harshil-Jani

examples/psbt_sign_finalize.rs

@@ -1,37 +1,56 @@
-// SPDX-License-Identifier: CC0-1.0
-
 use std::collections::BTreeMap;
 use std::str::FromStr;
 
+use bitcoin::sighash::SighashCache;
+use bitcoin::PrivateKey;
 use miniscript::bitcoin::consensus::encode::deserialize;
 use miniscript::bitcoin::hashes::hex::FromHex;
-use miniscript::bitcoin::psbt::{self, Psbt};
-use miniscript::bitcoin::sighash::SighashCache;
+use miniscript::bitcoin::psbt::PartiallySignedTransaction as Psbt;
 use miniscript::bitcoin::{
-    self, base64, secp256k1, Address, Network, OutPoint, PrivateKey, Script, Sequence, Transaction,
-    TxIn, TxOut,
+    self, base64, psbt, secp256k1, Address, Network, OutPoint, Script, Sequence, Transaction, TxIn,
+    TxOut,
 };
 use miniscript::psbt::{PsbtExt, PsbtInputExt};
-use miniscript::Descriptor;
+use miniscript::{Descriptor, DescriptorPublicKey};
 
 fn main() {
+    // Defining the descriptor keys
     let secp256k1 = secp256k1::Secp256k1::new();
-
-    let s = "wsh(t:or_c(pk(027a3565454fe1b749bccaef22aff72843a9c3efefd7b16ac54537a0c23f0ec0de),v:thresh(1,pkh(032d672a1a91cc39d154d366cd231983661b0785c7f27bc338447565844f4a6813),a:pkh(03417129311ed34c242c012cd0a3e0b9bca0065f742d0dfb63c78083ea6a02d4d9),a:pkh(025a687659658baeabdfc415164528065be7bcaade19342241941e556557f01e28))))#7hut9ukn";
-    let bridge_descriptor = Descriptor::from_str(&s).unwrap();
-    //let bridge_descriptor = Descriptor::<bitcoin::PublicKey>::from_str(&s).expect("parse descriptor string");
-    assert!(bridge_descriptor.sanity_check().is_ok());
-    println!(
-        "Bridge pubkey script: {}",
-        bridge_descriptor.script_pubkey()
+    let keys = vec![
+        "027a3565454fe1b749bccaef22aff72843a9c3efefd7b16ac54537a0c23f0ec0de",
+        "032d672a1a91cc39d154d366cd231983661b0785c7f27bc338447565844f4a6813",
+        "03417129311ed34c242c012cd0a3e0b9bca0065f742d0dfb63c78083ea6a02d4d9",
+        "025a687659658baeabdfc415164528065be7bcaade19342241941e556557f01e28",
+    ];
+    // The wsh descriptor indicates a Witness Script Hash, meaning the descriptor is for a SegWit script.
+    // wsh(or(pk(A),thresh(1,pkh(B),pkh(C),pkh(D))))
+
+    // Let's break it down:
+    // t:or_c specifies an "or" construct, which means the script can be satisfied by one of the given conditions:
+    // pk(A) OR thresh(1,pkh(B),pkh(C),pkh(D))
+    // Inside threshold condition atleast 1 out of all given conditions should satisfy.
+
+    // By constructing transactions using this wsh 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!(
+        "wsh(t:or_c(pk({}),v:thresh(1,pkh({}),a:pkh({}),a:pkh({}))))",
+        keys[0], // key A
+        keys[1], // key B
+        keys[2], // key C
+        keys[3], // key D
     );
+    let descriptor = Descriptor::from_str(&s).expect("parse descriptor string");
+
+    assert!(descriptor.sanity_check().is_ok());
+    println!("descriptor pubkey script: {}", descriptor.script_pubkey());
     println!(
-        "Bridge address: {}",
-        bridge_descriptor.address(Network::Regtest).unwrap()
+        "descriptor address: {}",
+        descriptor.address(Network::Regtest).unwrap()
     );
     println!(
         "Weight for witness satisfaction cost {}",
-        bridge_descriptor.max_weight_to_satisfy().unwrap()
+        descriptor.max_weight_to_satisfy().unwrap()
     );
 
     let master_private_key_str = "cQhdvB3McbBJdx78VSSumqoHQiSXs75qwLptqwxSQBNBMDxafvaw";
@@ -69,24 +88,14 @@ fn main() {
         _backup3_private.public_key(&secp256k1)
     );
 
+    // Create a spending transaction
     let spend_tx = Transaction {
         version: 2,
         lock_time: bitcoin::absolute::LockTime::from_consensus(5000),
         input: vec![],
         output: vec![],
     };
 
-    // Spend one input and spend one output for simplicity.
-    let mut psbt = Psbt {
-        unsigned_tx: spend_tx,
-        unknown: BTreeMap::new(),
-        proprietary: BTreeMap::new(),
-        xpub: BTreeMap::new(),
-        version: 0,
-        inputs: vec![],
-        outputs: vec![],
-    };
-
     let hex_tx = "020000000001018ff27041f3d738f5f84fd5ee62f1c5b36afebfb15f6da0c9d1382ddd0eaaa23c0000000000feffffff02b3884703010000001600142ca3b4e53f17991582d47b15a053b3201891df5200e1f50500000000220020c0ebf552acd2a6f5dee4e067daaef17b3521e283aeaa44a475278617e3d2238a0247304402207b820860a9d425833f729775880b0ed59dd12b64b9a3d1ab677e27e4d6b370700220576003163f8420fe0b9dc8df726cff22cbc191104a2d4ae4f9dfedb087fcec72012103817e1da42a7701df4db94db8576f0e3605f3ab3701608b7e56f92321e4d8999100000000";
     let depo_tx: Transaction = deserialize(&Vec::<u8>::from_hex(hex_tx).unwrap()).unwrap();
 
@@ -96,76 +105,99 @@ fn main() {
 
     let amount = 100000000;
 
-    let (outpoint, witness_utxo) = get_vout(&depo_tx, &bridge_descriptor.script_pubkey());
-
-    let mut txin = TxIn::default();
-    txin.previous_output = outpoint;
-
-    txin.sequence = Sequence::from_height(26); //Sequence::MAX; //
-    psbt.unsigned_tx.input.push(txin);
-
-    psbt.unsigned_tx.output.push(TxOut {
-        script_pubkey: receiver.script_pubkey(),
-        value: amount / 5 - 500,
-    });
-
-    psbt.unsigned_tx.output.push(TxOut {
-        script_pubkey: bridge_descriptor.script_pubkey(),
-        value: amount * 4 / 5,
-    });
-
-    // Generating signatures & witness data
+    let (outpoint, witness_utxo) = get_vout(&depo_tx, &descriptor.script_pubkey());
 
-    let mut input = psbt::Input::default();
-    input
-        .update_with_descriptor_unchecked(&bridge_descriptor)
-        .unwrap();
-
-    input.witness_utxo = Some(witness_utxo.clone());
-    psbt.inputs.push(input);
-    psbt.outputs.push(psbt::Output::default());
-
-    let mut sighash_cache = SighashCache::new(&psbt.unsigned_tx);
-
-    let msg = psbt
-        .sighash_msg(0, &mut sighash_cache, None)
+    let all_assets = Descriptor::<DescriptorPublicKey>::from_str(&s)
         .unwrap()
-        .to_secp_msg();
-
-    // Fixme: Take a parameter
-    let hash_ty = bitcoin::sighash::EcdsaSighashType::All;
-
-    let sk1 = backup1_private.inner;
-    let sk2 = backup2_private.inner;
-
-    // Finally construct the signature and add to psbt
-    let sig1 = secp256k1.sign_ecdsa(&msg, &sk1);
-    let pk1 = backup1_private.public_key(&secp256k1);
-    assert!(secp256k1.verify_ecdsa(&msg, &sig1, &pk1.inner).is_ok());
-
-    // Second key just in case
-    let sig2 = secp256k1.sign_ecdsa(&msg, &sk2);
-    let pk2 = backup2_private.public_key(&secp256k1);
-    assert!(secp256k1.verify_ecdsa(&msg, &sig2, &pk2.inner).is_ok());
-
-    psbt.inputs[0].partial_sigs.insert(
-        pk1,
-        bitcoin::ecdsa::Signature {
-            sig: sig1,
-            hash_ty: hash_ty,
-        },
-    );
-
-    println!("{:#?}", psbt);
-
-    let serialized = psbt.serialize();
-    println!("{}", base64::encode(&serialized));
-
-    psbt.finalize_mut(&secp256k1).unwrap();
-    println!("{:#?}", psbt);
+        .all_assets()
+        .unwrap();
 
-    let tx = psbt.extract_tx();
-    println!("{}", bitcoin::consensus::encode::serialize_hex(&tx));
+    for asset in all_assets {
+        // Spend one input and spend one output for simplicity.
+        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.script_pubkey(),
+            value: amount / 5 - 500,
+        });
+
+        psbt.unsigned_tx.output.push(TxOut {
+            script_pubkey: descriptor.script_pubkey(),
+            value: amount * 4 / 5,
+        });
+
+        // Consider that out of all the keys required to sign the descriptor, 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 one key available i.e Key A(as seen from the descriptor above)
+        // Key A is enough to satisfy the given descriptor because it is OR.
+        // We have to add the key to `Asset` and then obtain plan with only available signature if  the descriptor can be satisfied.
+
+        // Check the possible asset which we can use
+        println!("{:#?}", asset);
+
+        // Obtain the Plan based on available Assets
+        let plan = descriptor.clone().plan(&asset).unwrap();
+
+        // Creating a PSBT Input
+        let mut input = psbt::Input::default();
+
+        // Update the PSBT input from the result which we have obtained from the Plan.
+        plan.update_psbt_input(&mut input);
+        input.update_with_descriptor_unchecked(&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());
+
+        let mut sighash_cache = SighashCache::new(&psbt.unsigned_tx);
+
+        let msg = psbt
+            .sighash_msg(0, &mut sighash_cache, None)
+            .unwrap()
+            .to_secp_msg();
+
+        // Fixme: Take a parameter
+        let hash_ty = bitcoin::sighash::EcdsaSighashType::All;
+
+        let sk = backup1_private.inner;
+
+        // Finally construct the signature and add to psbt
+        let sig = secp256k1.sign_ecdsa(&msg, &sk);
+        let key_a = backup1_private.public_key(&secp256k1);
+        assert!(secp256k1.verify_ecdsa(&msg, &sig, &key_a.inner).is_ok());
+
+        psbt.inputs[0]
+            .partial_sigs
+            .insert(key_a, bitcoin::ecdsa::Signature { sig, hash_ty });
+
+        println!("{:#?}", psbt);
+
+        let serialized = psbt.serialize();
+        println!("{}", base64::encode(&serialized));
+
+        psbt.finalize_mut(&secp256k1).unwrap();
+        println!("{:#?}", psbt);
+
+        let tx = psbt.extract_tx();
+        println!("{}", bitcoin::consensus::encode::serialize_hex(&tx));
+    }
 }
 
 // Find the Outpoint by spk