Merge pull request #7179 from BitGo/BTC-2634-convert-to-supported-prefixes

fix: convert unsupported utxolib prefixes

Author: lcovar

modules/abstract-lightning/src/lightning/lightningUtils.ts

@@ -114,17 +114,19 @@ export function addIPCaveatToMacaroon(macaroonBase64: string, ip: string): strin
   return bytesToBase64(macaroon.exportBinary());
 }
 
-const PURPOSE_WRAPPED_P2WKH = 49;
-const PURPOSE_P2WKH = 84;
-const PURPOSE_P2TR = 86;
-const PURPOSE_ALL_OTHERS = 1017;
+export const PURPOSE_WRAPPED_P2WKH = 49;
+export const PURPOSE_P2WKH = 84;
+export const PURPOSE_P2TR = 86;
+export const PURPOSE_ALL_OTHERS = 1017;
 
-type ExtendedKeyPurpose =
+export type ExtendedKeyPurpose =
   | typeof PURPOSE_WRAPPED_P2WKH
   | typeof PURPOSE_P2WKH
   | typeof PURPOSE_P2TR
   | typeof PURPOSE_ALL_OTHERS;
 
+export type ExtendedKeyAddressPurpose = typeof PURPOSE_WRAPPED_P2WKH | typeof PURPOSE_P2WKH | typeof PURPOSE_P2TR;
+
 /**
  * Converts an extended public key (xpub) to the appropriate prefix (ypub, vpub, etc.) based on its purpose and network.
  */
@@ -151,6 +153,43 @@ function convertXpubPrefix(xpub: string, purpose: ExtendedKeyPurpose, isMainnet:
   return bs58check.encode(data);
 }
 
+/**
+ * Converts a prefix related to purpose and network (ypub, vpub, etc.) to extended public key (xpub).
+ */
+export function revertXpubPrefix(xpub: string, purpose: ExtendedKeyPurpose, isMainnet: boolean): string {
+  // If the purpose is P2TR or ALL_OTHERS, the key is already in the standard format (xpub/tpub),
+  // so we return it unmodified. This is the same bypass condition.
+  if (purpose === PURPOSE_P2TR || purpose === PURPOSE_ALL_OTHERS) {
+    return xpub;
+  }
+
+  // 1. Decode the extended public key to get the raw bytes
+  const data = bs58check.decode(xpub);
+
+  let versionBytes: Buffer;
+
+  // 2. Determine the standard prefix (xpub/tpub) based on the network
+  switch (purpose) {
+    case PURPOSE_WRAPPED_P2WKH:
+    case PURPOSE_P2WKH:
+      // All standard, non-SegWit-specific keys use the same prefix (xpub for mainnet, tpub for testnet)
+      versionBytes = isMainnet
+        ? Buffer.from([0x04, 0x88, 0xb2, 0x1e]) // xpub
+        : Buffer.from([0x04, 0x35, 0x87, 0xcf]); // tpub
+      break;
+    default:
+      // This case should ideally not be hit if the input key is one of the converted types
+      throw new Error('Unsupported purpose for reversal');
+  }
+
+  // 3. Overwrite the existing prefix (ypub, zpub, upub, or vpub)
+  // with the standard xpub or tpub prefix.
+  versionBytes.copy(data, 0, 0, 4);
+
+  // 4. Encode the modified byte data back to a Base58Check string
+  return bs58check.encode(data);
+}
+
 /**
  * Derives watch-only accounts from the master HD node for the given purposes and network.
  */

modules/abstract-lightning/src/lightning/parseWithdrawPsbt.ts

@@ -1,18 +1,28 @@
 import * as utxolib from '@bitgo/utxo-lib';
-import { Psbt } from '@bitgo/utxo-lib';
+import { isMainnet, Psbt } from '@bitgo/utxo-lib';
 import { WatchOnlyAccount, WithdrawBaseOutputUTXO } from '../codecs';
 import { LightningOnchainRecipient } from '@bitgo/public-types';
 import { Bip32Derivation } from 'bip174/src/lib/interfaces';
+import {
+  ExtendedKeyAddressPurpose,
+  PURPOSE_P2TR,
+  PURPOSE_P2WKH,
+  PURPOSE_WRAPPED_P2WKH,
+  revertXpubPrefix,
+} from './lightningUtils';
 
 function parseDerivationPath(derivationPath: string): {
-  purpose: number;
+  purpose: ExtendedKeyAddressPurpose;
   change: number;
   addressIndex: number;
 } {
   const pathSegments = derivationPath.split('/');
   const purpose = Number(pathSegments[1].replace(/'/g, ''));
   const change = Number(pathSegments[pathSegments.length - 2]);
   const addressIndex = Number(pathSegments[pathSegments.length - 1]);
+  if (purpose !== PURPOSE_WRAPPED_P2WKH && purpose !== PURPOSE_P2WKH && purpose !== PURPOSE_P2TR) {
+    throw new Error(`Unsupported purpose in derivation path: ${purpose}`);
+  }
   return { purpose, change, addressIndex };
 }
 
@@ -65,8 +75,10 @@ function verifyChangeAddress(
     throw new Error(`Account not found for purpose: ${purpose}`);
   }
 
+  // convert upub, vpub, etc prefixes to xpub as utxolib doesn't support these
+  const convertedXpub = revertXpubPrefix(account.xpub, purpose, isMainnet(network));
   // Create a BIP32 node from the xpub
-  const xpubNode = utxolib.bip32.fromBase58(account.xpub, network);
+  const xpubNode = utxolib.bip32.fromBase58(convertedXpub, network);
 
   // Derive the public key from the xpub using the change and address index
   const derivedPubkey = xpubNode.derive(change).derive(addressIndex).publicKey;