Merge pull request #8859 from BitGo/otto/derive-key-with-seed

refactor(abstract-utxo): inline deriveKeyWithSeed to drop utxolib BIP32 bridge

Author: OttoAllmendinger

modules/abstract-utxo/src/deriveKeyWithSeed.ts

@@ -0,0 +1,19 @@
+import { createHash } from 'crypto';
+
+import type { BIP32 } from '@bitgo/wasm-utxo';
+
+/**
+ * Derive a child key from `key` using a path determined by `seed`.
+ *
+ * Mirrors `BaseCoin.deriveKeyWithSeedBip32` from sdk-core but operates on
+ * wasm-utxo's BIP32 class (which has the same `derivePath` semantics).
+ */
+export function deriveKeyWithSeed(key: BIP32, seed: string): { key: BIP32; derivationPath: string } {
+  const sha = (input: string | Buffer): Buffer => createHash('sha256').update(input).digest();
+  const derivationPathInput = sha(sha(seed)).toString('hex');
+  const derivationPath = `m/999999/${parseInt(derivationPathInput.slice(0, 7), 16)}/${parseInt(
+    derivationPathInput.slice(7, 14),
+    16
+  )}`;
+  return { key: key.derivePath(derivationPath), derivationPath };
+}

modules/abstract-utxo/src/impl/btc/inscriptionBuilder.ts

@@ -1,7 +1,6 @@
 import assert from 'assert';
 
 import {
-  BaseCoin,
   HalfSignedUtxoTransaction,
   IInscriptionBuilder,
   IWallet,
@@ -29,8 +28,8 @@ import {
 import { BIP32, fixedScriptWallet } from '@bitgo/wasm-utxo';
 
 import { AbstractUtxoCoin } from '../../abstractUtxoCoin';
+import { deriveKeyWithSeed } from '../../deriveKeyWithSeed';
 import { fetchKeychains } from '../../keychains';
-import { toUtxolibBIP32 } from '../../wasmUtil';
 
 /** Key identifier for signing */
 type SignerKey = 'user' | 'backup' | 'bitgo';
@@ -58,8 +57,7 @@ export class InscriptionBuilder implements IInscriptionBuilder {
     const user = await this.wallet.baseCoin.keychains().get({ id: this.wallet.keyIds()[KeyIndices.USER] });
     assert(user.pub);
 
-    const userKey = toUtxolibBIP32(BIP32.fromBase58(user.pub));
-    const { key: derivedKey } = BaseCoin.deriveKeyWithSeedBip32(userKey, inscriptionData.toString());
+    const { key: derivedKey } = deriveKeyWithSeed(BIP32.fromBase58(user.pub), inscriptionData.toString());
 
     const result = inscriptions.createInscriptionRevealData(
       derivedKey.publicKey,

modules/abstract-utxo/src/offlineVault/OfflineVaultHalfSigned.ts

@@ -1,8 +1,7 @@
 import { BIP32, bip32, Psbt } from '@bitgo/wasm-utxo';
-import { BaseCoin } from '@bitgo/sdk-core';
 
+import { deriveKeyWithSeed } from '../deriveKeyWithSeed';
 import { UtxoCoinName } from '../names';
-import { toUtxolibBIP32 } from '../wasmUtil';
 
 import { OfflineVaultSignable } from './OfflineVaultSignable';
 import { DescriptorTransaction, getHalfSignedPsbt } from './descriptor';
@@ -21,8 +20,8 @@ export function createHalfSigned(
   derivationId: string,
   tx: unknown
 ): OfflineVaultHalfSigned {
-  const key = typeof prv === 'string' ? BIP32.fromBase58(prv) : prv;
-  const derivedKey = BaseCoin.deriveKeyWithSeedBip32(toUtxolibBIP32(key), derivationId).key;
+  const wasmKey = typeof prv === 'string' ? BIP32.fromBase58(prv) : BIP32.fromBase58(prv.toBase58());
+  const derivedKey = deriveKeyWithSeed(wasmKey, derivationId).key;
   if (!OfflineVaultSignable.is(tx)) {
     throw new Error('unsupported transaction type');
   }

modules/abstract-utxo/test/unit/deriveKeyWithSeed.ts

@@ -0,0 +1,31 @@
+import * as assert from 'assert';
+
+import * as utxolib from '@bitgo/utxo-lib';
+import { BIP32 } from '@bitgo/wasm-utxo';
+import { BaseCoin } from '@bitgo/sdk-core';
+
+import { deriveKeyWithSeed } from '../../src/deriveKeyWithSeed';
+
+// Deterministic test xprv — derived from a 32-byte all-ones seed.
+const XPRV =
+  'xprv9s21ZrQH143K2QPmabzR6Q9tkNRfFxy1jy9p1PRctypZJWAjtjWBJAxxvQ3454vPpnUoLfGH8YP5KcHFX4Z5Jh7bYnFuBhxztHRy72yXmnC';
+
+const SEEDS = ['', 'hello', 'some long seed string with spaces', '\u{1F600}'];
+
+describe('deriveKeyWithSeed', function () {
+  for (const seed of SEEDS) {
+    it(`matches BaseCoin.deriveKeyWithSeedBip32 for seed ${JSON.stringify(seed)}`, function () {
+      const wasmKey = BIP32.fromBase58(XPRV);
+      const utxolibKey = utxolib.bip32.fromBase58(XPRV);
+
+      const wasmResult = deriveKeyWithSeed(wasmKey, seed);
+      const sdkCoreResult = BaseCoin.deriveKeyWithSeedBip32(utxolibKey, seed);
+
+      assert.strictEqual(wasmResult.derivationPath, sdkCoreResult.derivationPath);
+      assert.strictEqual(
+        Buffer.from(wasmResult.key.publicKey).toString('hex'),
+        Buffer.from(sdkCoreResult.key.publicKey).toString('hex')
+      );
+    });
+  }
+});