feat(utxo-core): implement buildToSignPsbt for BIP322 message signing

Add functionality to construct the toSign PSBT for BIP322 message verification
with support for redeem scripts and witness scripts. Includes tests to verify
correctness against BIP322 test vectors.

Supports v0 segwit and non-segwit addresses. Taproot to be added later.

Issue: BTC-2360

Co-authored-by: llm-git <[email protected]>

Author: davidkaplanbitgo

modules/utxo-core/src/bip322/index.ts

@@ -1 +1,2 @@
 export * from './toSpend';
+export * from './toSign';

modules/utxo-core/src/bip322/toSign.ts

@@ -0,0 +1,49 @@
+import { Psbt, Transaction } from '@bitgo/utxo-lib';
+
+export type AddressDetails = {
+  redeemScript?: Buffer;
+  witnessScript?: Buffer;
+};
+
+/**
+ * Construct the toSign PSBT for a BIP322 verification.
+ * Source implementation:
+ * https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki#full
+ *
+ * @param {string} toSpendTxHex - The hex representation of the `toSpend` transaction.
+ * @param {AddressDetails} addressDetails - The details of the address, including redeemScript and/or witnessScript.
+ * @returns {string} - The hex representation of the constructed PSBT.
+ */
+export function buildToSignPsbt(toSpendTxHex: string, addressDetails: AddressDetails): string {
+  if (!addressDetails.redeemScript && !addressDetails.witnessScript) {
+    throw new Error('redeemScript and/or witnessScript must be provided');
+  }
+
+  const toSpendTx = Transaction.fromHex(toSpendTxHex);
+
+  // Create PSBT object for constructing the transaction
+  const psbt = new Psbt();
+  // Set default value for nVersion and nLockTime
+  psbt.setVersion(0); // nVersion = 0
+  psbt.setLocktime(0); // nLockTime = 0
+  // Set the input
+  psbt.addInput({
+    hash: toSpendTx.getId(), // vin[0].prevout.hash = to_spend.txid
+    index: 0, // vin[0].prevout.n = 0
+    sequence: 0, // vin[0].nSequence = 0
+    nonWitnessUtxo: toSpendTx.toBuffer(), // previous transaction for us to rebuild later to verify
+  });
+  if (addressDetails.redeemScript) {
+    psbt.updateInput(0, { redeemScript: addressDetails.redeemScript });
+  }
+  if (addressDetails.witnessScript) {
+    psbt.updateInput(0, { witnessUtxo: { value: BigInt(0), script: addressDetails.witnessScript } });
+  }
+
+  // Set the output
+  psbt.addOutput({
+    value: BigInt(0), // vout[0].nValue = 0
+    script: Buffer.from([0x6a]), // vout[0].scriptPubKey = OP_RETURN
+  });
+  return psbt.toHex();
+}

modules/utxo-core/test/bip322/toSign.ts

@@ -0,0 +1,43 @@
+import assert from 'assert';
+
+import { payments, Psbt, ECPair, Transaction } from '@bitgo/utxo-lib';
+
+import * as bip322 from '../../src/bip322';
+
+describe('BIP322 toSign', function () {
+  describe('buildToSignPsbt', function () {
+    const WIF = 'L3VFeEujGtevx9w18HD1fhRbCH67Az2dpCymeRE1SoPK6XQtaN2k';
+    const prv = ECPair.fromWIF(WIF);
+    const scriptPubKey = payments.p2wpkh({
+      address: 'bc1q9vza2e8x573nczrlzms0wvx3gsqjx7vavgkx0l',
+    }).output as Buffer;
+
+    // Source: https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki#transaction-hashes
+    const fixtures = [
+      {
+        message: '',
+        txid: '1e9654e951a5ba44c8604c4de6c67fd78a27e81dcadcfe1edf638ba3aaebaed6',
+      },
+      {
+        message: 'Hello World',
+        txid: '88737ae86f2077145f93cc4b153ae9a1cb8d56afa511988c149c5c8c9d93bddf',
+      },
+    ];
+
+    fixtures.forEach(({ message, txid }) => {
+      it(`should build a to_sign PSBT for message "${message}"`, function () {
+        const toSpendTxHex = bip322.buildToSpendTransaction(scriptPubKey, Buffer.from(message));
+        const addressDetails = {
+          witnessScript: scriptPubKey,
+        };
+        const result = bip322.buildToSignPsbt(toSpendTxHex, addressDetails);
+        const computedTxid = Psbt.fromHex(result)
+          .signAllInputs(prv, [Transaction.SIGHASH_ALL])
+          .finalizeAllInputs()
+          .extractTransaction()
+          .getId();
+        assert.strictEqual(computedTxid, txid, `Transaction ID for message "${message}" does not match expected value`);
+      });
+    });
+  });
+});