feat(utxo-core): add utility functions for PSBT message proofs

Add utility functions for working with BIP322 message signatures in PSBTs,
including functions to add proof messages, check if a PSBT contains a
BIP322 proof, and locate the input index for a BIP322 message.

Issue: BTC-2361

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

Author: davidkaplanbitgo

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

@@ -1,2 +1,3 @@
 export * from './toSpend';
 export * from './toSign';
+export * from './utils';

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

@@ -0,0 +1,30 @@
+import * as utxolib from '@bitgo/utxo-lib';
+
+export function addBip322ProofMessage(psbt: utxolib.bitgo.UtxoPsbt, inputIndex: number, message: Buffer): void {
+  utxolib.bitgo.addProprietaryKeyValuesFromUnknownKeyValues(psbt, 'input', inputIndex, {
+    key: {
+      identifier: utxolib.bitgo.PSBT_PROPRIETARY_IDENTIFIER,
+      subtype: utxolib.bitgo.ProprietaryKeySubtype.BIP322_MESSAGE,
+      keydata: Buffer.alloc(0),
+    },
+    value: message,
+  });
+}
+
+export function getBip322ProofInputIndex(psbt: utxolib.Psbt): number | undefined {
+  const res = psbt.data.inputs.flatMap((input, inputIndex) => {
+    const proprietaryKeyVals = utxolib.bitgo.getPsbtInputProprietaryKeyVals(input, {
+      identifier: utxolib.bitgo.PSBT_PROPRIETARY_IDENTIFIER,
+      subtype: utxolib.bitgo.ProprietaryKeySubtype.BIP322_MESSAGE,
+    });
+    if (proprietaryKeyVals.length > 1) {
+      throw new Error(`Multiple BIP322 messages found at input index ${inputIndex}`);
+    }
+    return proprietaryKeyVals.length === 0 ? [] : [inputIndex];
+  });
+  return res.length === 0 ? undefined : res[0];
+}
+
+export function psbtIsBip322Proof(psbt: utxolib.Psbt): boolean {
+  return getBip322ProofInputIndex(psbt) !== undefined;
+}

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

@@ -1,7 +1,18 @@
 import { payments, ECPair } from '@bitgo/utxo-lib';
 
+import { buildToSignPsbt, buildToSpendTransaction } from '../../src/bip322';
+
 export const BIP322_WIF_FIXTURE = 'L3VFeEujGtevx9w18HD1fhRbCH67Az2dpCymeRE1SoPK6XQtaN2k';
 export const BIP322_PRV_FIXTURE = ECPair.fromWIF(BIP322_WIF_FIXTURE);
 export const BIP322_PAYMENT_P2WPKH_FIXTURE = payments.p2wpkh({
   address: 'bc1q9vza2e8x573nczrlzms0wvx3gsqjx7vavgkx0l',
 });
+
+export const BIP322_FIXTURE_HELLO_WORLD_TOSPEND_TX = buildToSpendTransaction(
+  BIP322_PAYMENT_P2WPKH_FIXTURE.output as Buffer,
+  Buffer.from('Hello World')
+);
+
+export const BIP322_FIXTURE_HELLOW_WORLD_TOSIGN_PSBT = buildToSignPsbt(BIP322_FIXTURE_HELLO_WORLD_TOSPEND_TX, {
+  witnessScript: BIP322_PAYMENT_P2WPKH_FIXTURE.output as Buffer,
+});

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

@@ -0,0 +1,46 @@
+import assert from 'assert';
+
+import * as utxolib from '@bitgo/utxo-lib';
+
+import { addBip322ProofMessage, getBip322ProofInputIndex, psbtIsBip322Proof } from '../../src/bip322';
+
+import { BIP322_FIXTURE_HELLOW_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(),
+      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], {
+      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].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(),
+      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.ok(psbtIsBip322Proof(psbt));
+  });
+});