feat(utxo-core): simplify signature process with direct message param

Refactor buildToSignPsbt to accept message directly instead of a toSpendTx
parameter. This simplifies the API by internally generating the toSpend
transaction and storing the message in the PSBT for later verification.

Also adds message to the PSBT as proprietary data so it can be verified
during the validation process.

Issue: BTC-2375

Author: davidkaplanbitgo

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

@@ -1,6 +1,7 @@
-import { Psbt, Transaction, bitgo } from '@bitgo/utxo-lib';
+import { Psbt, bitgo } from '@bitgo/utxo-lib';
 
-import { isTaprootChain } from './utils';
+import { addBip322ProofMessage, isTaprootChain } from './utils';
+import { BIP322_TAG, buildToSpendTransaction } from './toSpend';
 
 export type AddressDetails = {
   redeemScript?: Buffer;
@@ -13,11 +14,14 @@ export type AddressDetails = {
  * Source implementation:
  * https://github.com/bitcoin/bips/blob/master/bip-0322.mediawiki#full
  *
- * @param {string} toSpendTxHex - The hex representation of the `toSpend` transaction.
+ * @param {string} message - The message that is hashed into the `to_spend` transaction.
  * @param {AddressDetails} addressDetails - The details of the address, including redeemScript and/or witnessScript.
- * @returns {string} - The hex representation of the constructed PSBT.
+ * @param {string} [tag=BIP322_TAG] - The tag to use for hashing, defaults to BIP322_TAG.
+ * @returns {Psbt} - The hex representation of the constructed PSBT.
  */
-export function buildToSignPsbt(toSpendTx: Transaction<bigint>, addressDetails: AddressDetails): Psbt {
+export function buildToSignPsbt(message: string, addressDetails: AddressDetails, tag = BIP322_TAG): Psbt {
+  const toSpendTx = buildToSpendTransaction(addressDetails.scriptPubKey, message, tag);
+
   // Create PSBT object for constructing the transaction
   const psbt = new Psbt();
   // Set default value for nVersion and nLockTime
@@ -41,6 +45,9 @@ export function buildToSignPsbt(toSpendTx: Transaction<bigint>, addressDetails:
     psbt.updateInput(0, { witnessScript: addressDetails.witnessScript });
   }
 
+  // Add the message as a proprietary key value to the PSBT so we can verify it later
+  addBip322ProofMessage(psbt as bitgo.UtxoPsbt, 0, Buffer.from(message));
+
   // Set the output
   psbt.addOutput({
     value: BigInt(0), // vout[0].nValue = 0
@@ -50,7 +57,7 @@ export function buildToSignPsbt(toSpendTx: Transaction<bigint>, addressDetails:
 }
 
 export function buildToSignPsbtForChainAndIndex(
-  toSpendTx: Transaction<bigint>,
+  message: string,
   rootWalletKeys: bitgo.RootWalletKeys,
   chain: bitgo.ChainCode,
   index: number
@@ -63,12 +70,7 @@ export function buildToSignPsbtForChainAndIndex(
     bitgo.scriptTypeForChain(chain)
   );
 
-  const toSpendScriptPubKey = toSpendTx.outs[0].script;
-  if (!toSpendScriptPubKey.equals(output.scriptPubKey)) {
-    throw new Error('Output scriptPubKey does not match the expected output script for the chain and index.');
-  }
-
-  return buildToSignPsbt(toSpendTx, {
+  return buildToSignPsbt(message, {
     scriptPubKey: output.scriptPubKey,
     redeemScript: output.redeemScript,
     witnessScript: output.witnessScript,

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

@@ -13,6 +13,6 @@ export const BIP322_FIXTURE_HELLO_WORLD_TOSPEND_TX = buildToSpendTransaction(
   Buffer.from('Hello World')
 );
 
-export const BIP322_FIXTURE_HELLOW_WORLD_TOSIGN_PSBT = buildToSignPsbt(BIP322_FIXTURE_HELLO_WORLD_TOSPEND_TX, {
+export const BIP322_FIXTURE_HELLO_WORLD_TOSIGN_PSBT = buildToSignPsbt('Hello World', {
   scriptPubKey: BIP322_PAYMENT_P2WPKH_FIXTURE.output as Buffer,
 });

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

@@ -23,11 +23,9 @@ describe('BIP322 toSign', function () {
 
     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 = {
+        const result = bip322.buildToSignPsbt(message, {
           scriptPubKey,
-        };
-        const result = bip322.buildToSignPsbt(toSpendTx, addressDetails);
+        });
         const computedTxid = result
           .signAllInputs(prv, [utxolib.Transaction.SIGHASH_ALL])
           .finalizeAllInputs()
@@ -41,13 +39,6 @@ describe('BIP322 toSign', function () {
   describe('buildToSignPsbtForChainAndIndex', function () {
     const rootWalletKeys = utxolib.testutil.getDefaultWalletKeys();
 
-    it('should fail when scriptPubKey of to_spend is different than to_sign', function () {
-      const toSpendTx = bip322.buildToSpendTransaction(BIP322_PAYMENT_P2WPKH_FIXTURE.output as Buffer, 'Hello World');
-      assert.throws(() => {
-        bip322.buildToSignPsbtForChainAndIndex(toSpendTx, rootWalletKeys, 0, 0);
-      }, /Output scriptPubKey does not match the expected output script for the chain and index./);
-    });
-
     function run(chain: utxolib.bitgo.ChainCode, shouldFail: boolean, index: number) {
       it(`should${
         shouldFail ? ' fail to' : ''
@@ -60,7 +51,7 @@ describe('BIP322 toSign', function () {
           return;
         }
         const toSpendTx = bip322.buildToSpendTransactionFromChainAndIndex(rootWalletKeys, chain, index, message);
-        const toSignPsbt = bip322.buildToSignPsbtForChainAndIndex(toSpendTx, rootWalletKeys, chain, index);
+        const toSignPsbt = bip322.buildToSignPsbtForChainAndIndex(message, rootWalletKeys, chain, index);
 
         const derivedKeys = rootWalletKeys.deriveForChainAndIndex(chain, index);
         const prv1 = derivedKeys.triple[0];

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

@@ -2,45 +2,37 @@ import assert from 'assert';
 
 import * as utxolib from '@bitgo/utxo-lib';
 
-import { addBip322ProofMessage, getBip322ProofInputIndex, psbtIsBip322Proof } from '../../src/bip322';
+import { getBip322ProofInputIndex, psbtIsBip322Proof } from '../../src/bip322';
 
-import { BIP322_FIXTURE_HELLOW_WORLD_TOSIGN_PSBT } from './bip322.utils';
+import { BIP322_FIXTURE_HELLO_WORLD_TOSIGN_PSBT } from './bip322.utils';
 
 describe('BIP322 Proof utils', function () {
   it('should add a BIP322 proof message to a PSBT input', function () {
     const psbt = utxolib.bitgo.createPsbtFromBuffer(
-      BIP322_FIXTURE_HELLOW_WORLD_TOSIGN_PSBT.toBuffer(),
+      BIP322_FIXTURE_HELLO_WORLD_TOSIGN_PSBT.toBuffer(),
       utxolib.networks.bitcoin
     );
-    const inputIndex = 0;
-    const message = Buffer.from('Hello World');
-    addBip322ProofMessage(psbt, inputIndex, message);
 
-    const proprietaryKeyVals = utxolib.bitgo.getPsbtInputProprietaryKeyVals(psbt.data.inputs[inputIndex], {
+    const proprietaryKeyVals = utxolib.bitgo.getPsbtInputProprietaryKeyVals(psbt.data.inputs[0], {
       identifier: utxolib.bitgo.PSBT_PROPRIETARY_IDENTIFIER,
       subtype: utxolib.bitgo.ProprietaryKeySubtype.BIP322_MESSAGE,
     });
 
     assert.ok(proprietaryKeyVals.length === 1);
-    assert.ok(proprietaryKeyVals[0].value.equals(message));
+    assert.ok(proprietaryKeyVals[0].value.equals(Buffer.from('Hello World')));
     assert.ok(proprietaryKeyVals[0].key.keydata.length === 0); // keydata should be empty
     assert.ok(proprietaryKeyVals[0].key.identifier === utxolib.bitgo.PSBT_PROPRIETARY_IDENTIFIER);
     assert.ok(proprietaryKeyVals[0].key.subtype === utxolib.bitgo.ProprietaryKeySubtype.BIP322_MESSAGE);
   });
 
   it('should return the input index of a BIP322 proof message', function () {
     const psbt = utxolib.bitgo.createPsbtFromBuffer(
-      BIP322_FIXTURE_HELLOW_WORLD_TOSIGN_PSBT.toBuffer(),
+      BIP322_FIXTURE_HELLO_WORLD_TOSIGN_PSBT.toBuffer(),
       utxolib.networks.bitcoin
     );
-    assert.ok(!psbtIsBip322Proof(psbt)); // initially should not be a BIP322 proof
-
-    const inputIndex = 0;
-    const message = Buffer.from('Hello World');
-    addBip322ProofMessage(psbt, inputIndex, message);
 
     const resultIndex = getBip322ProofInputIndex(psbt);
-    assert.strictEqual(resultIndex, inputIndex);
+    assert.strictEqual(resultIndex, 0);
     assert.ok(psbtIsBip322Proof(psbt));
   });
 });