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

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(toSpendTx: Transaction<bigint>, addressDetails: AddressDetails): Psbt {
+  if (!addressDetails.redeemScript && !addressDetails.witnessScript) {
+    throw new Error('redeemScript and/or witnessScript must be provided');
+  }
+
+  // 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;
+}

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

@@ -1,5 +1,5 @@
 import { Hash } from 'fast-sha256';
-import { Psbt } from '@bitgo/utxo-lib';
+import { Psbt, Transaction } from '@bitgo/utxo-lib';
 
 export const BIP322_TAG = 'BIP0322-signed-message';
 
@@ -31,9 +31,13 @@ export function hashMessageWithTag(message: string | Buffer, tag = BIP322_TAG):
  * @param {Buffer} scriptPubKey - The scriptPubKey to use for the output
  * @param {string | Buffer} message - The message to include in the transaction
  * @param {Buffer} [tag=BIP322_TAG] - The tag to use for hashing, defaults to BIP322_TAG.
- * @returns {string} - The hex representation of the constructed transaction
+ * @returns {Transaction} - The constructed transaction
  */
-export function buildToSpendTransaction(scriptPubKey: Buffer, message: string | Buffer, tag = BIP322_TAG): string {
+export function buildToSpendTransaction(
+  scriptPubKey: Buffer,
+  message: string | Buffer,
+  tag = BIP322_TAG
+): Transaction<bigint> {
   // Create PSBT object for constructing the transaction
   const psbt = new Psbt();
   // Set default value for nVersion and nLockTime
@@ -60,5 +64,5 @@ export function buildToSpendTransaction(scriptPubKey: Buffer, message: string |
     script: scriptPubKey, // vout[0].scriptPubKey = message_challenge
   });
   // Return transaction
-  return psbt.extractTransaction().toHex();
+  return psbt.extractTransaction();
 }

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

@@ -0,0 +1,43 @@
+import assert from 'assert';
+
+import { payments, 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 "${message}"`, function () {
+        const toSpendTx = bip322.buildToSpendTransaction(scriptPubKey, Buffer.from(message));
+        const addressDetails = {
+          witnessScript: scriptPubKey,
+        };
+        const result = bip322.buildToSignPsbt(toSpendTx, addressDetails);
+        const computedTxid = result
+          .signAllInputs(prv, [Transaction.SIGHASH_ALL])
+          .finalizeAllInputs()
+          .extractTransaction()
+          .getId();
+        assert.strictEqual(computedTxid, txid, `Transaction ID for message "${message}" does not match expected value`);
+      });
+    });
+  });
+});

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

@@ -1,6 +1,6 @@
 import assert from 'assert';
 
-import { payments, Transaction } from '@bitgo/utxo-lib';
+import { payments } from '@bitgo/utxo-lib';
 
 import { buildToSpendTransaction, hashMessageWithTag } from '../../src/bip322';
 
@@ -50,7 +50,7 @@ describe('to_spend', function () {
     fixtures.forEach(({ message, txid }) => {
       it(`should build a to_spend transaction for message "${message}"`, function () {
         const result = buildToSpendTransaction(scriptPubKey, Buffer.from(message));
-        const computedTxid = Transaction.fromHex(result).getId();
+        const computedTxid = result.getId();
         assert.strictEqual(computedTxid, txid, `Transaction ID for message "${message}" does not match expected value`);
       });
     });