Merge pull request #2466 from BlueWallet/fix-multisig-with-electrum

FIX: better support cosigning with Electrum desktop (closes #2401)

class/wallets/multisig-hd-wallet.js

@@ -991,7 +991,7 @@ export class MultisigHDWallet extends AbstractHDElectrumWallet {
    */
   cosignPsbt(psbt) {
     for (let cc = 0; cc < psbt.inputCount; cc++) {
-      for (const cosigner of this._cosigners) {
+      for (const [cosignerIndex, cosigner] of this._cosigners.entries()) {
         if (!MultisigHDWallet.isXpubString(cosigner)) {
           // ok this is a mnemonic, lets try to sign
           const seed = bip39.mnemonicToSeed(cosigner);
@@ -999,6 +999,34 @@ export class MultisigHDWallet extends AbstractHDElectrumWallet {
           try {
             psbt.signInputHD(cc, hdRoot);
           } catch (_) {} // protects agains duplicate cosignings
+
+          if (!psbt.inputHasHDKey(cc, hdRoot)) {
+            // failed signing as HD. probably bitcoinjs-lib could not match provided hdRoot's
+            // fingerprint (or path?) to the ones in psbt, which is the case of stupid Electrum desktop which can
+            // put bullshit paths and fingerprints in created psbt.
+            // lets try to find correct priv key and sign manually.
+            for (const derivation of psbt.data.inputs[cc].bip32Derivation || []) {
+              // okay, here we assume that fingerprint is irrelevant, but ending of the path is somewhat correct and
+              // correctly points to `/internal/index`, so we extract pubkey from our stored mnemonics+path and
+              // match it to the one provided in PSBT's input, and if we have a match - we are in luck! we can sign
+              // with this private key.
+              const seed = bip39.mnemonicToSeed(cosigner);
+              const root = HDNode.fromSeed(seed);
+              const splt = derivation.path.split('/');
+              const internal = +splt[splt.length - 2];
+              const index = +splt[splt.length - 1];
+
+              const path = this.getCustomDerivationPathForCosigner(cosignerIndex + 1) + `/${internal ? 1 : 0}/${index}`;
+              // ^^^ we assume that counterparty has Zpub for specified derivation path
+              const child = root.derivePath(path);
+              if (psbt.inputHasPubkey(cc, child.publicKey)) {
+                const keyPair = bitcoin.ECPair.fromPrivateKey(child.privateKey);
+                try {
+                  psbt.signInput(cc, keyPair);
+                } catch (_) {}
+              }
+            }
+          }
         }
       }
     }

tests/unit/multisig-hd-wallet.test.js

@@ -1052,6 +1052,32 @@ describe('multisig-wallet (native segwit)', () => {
     assert.ok(tx.toHex());
   });
 
+  it('can cosign PSBT that comes from electrum', async () => {
+    const wallet = new MultisigHDWallet();
+    wallet.setSecret(
+      'Name: Multisig Vault\n' +
+        'Policy: 2 of 2\n' +
+        "Derivation: m/48'/0'/0'/2'\n" +
+        'Format: P2WSH\n' +
+        '\n' +
+        '00000000: Zpub6yjw2xcmSY3uD1KbYLnrSuP2PaxDXajA1YymjzstkZCGnBX3Z1oC6dVFtA1TQNPoTaguixnjYfRK3edDDoP3xxJZSSv1S9NrG5zqK5YzKHE\n' +
+        '\n' +
+        'seed: point match rack notable poverty welcome slice stem warfare later skirt dream',
+    );
+
+    const psbt = bitcoin.Psbt.fromBase64(
+      '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',
+    );
+    assert.strictEqual(wallet.calculateHowManySignaturesWeHaveFromPsbt(psbt), 1);
+
+    const { tx } = wallet.cosignPsbt(psbt); // <---------------------------------------------------------
+
+    assert.strictEqual(wallet.calculateHowManySignaturesWeHaveFromPsbt(psbt), 2);
+    assert.ok(tx);
+    assert.throws(() => psbt.finalizeAllInputs()); // as it is already finalized
+    assert.ok(tx.toHex());
+  });
+
   it('can export/import when one of cosigners is mnemonic seed', async () => {
     const path = "m/48'/0'/0'/2'";