feat(statics): add middleware public key field to LightningNetwork

Add a new field to LightningNetwork interface that stores the middleware
public key used for deriving shared ECDH secrets between user's extended
private key and the middleware service.

BTC-2202

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

TICKET: BTC-2202

Author: davidkaplanbitgo

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

@@ -206,3 +206,13 @@ export function deriveLightningServiceSharedSecret(coinName: 'lnbtc' | 'tlnbtc',
   const userAuthHdNode = utxolib.bip32.fromBase58(userAuthXprv);
   return sdkcore.getSharedSecret(userAuthHdNode, publicKey);
 }
+
+/**
+ * Derives the shared secret for the middleware using the user's auth extended private key and the middleware's public key.
+ * This is used for secure communication between the middleware and the user's key.
+ */
+export function deriveMiddlewareSharedSecret(coinName: 'lnbtc' | 'tlnbtc', userXprv: string): Buffer {
+  const publicKey = Buffer.from(getStaticsLightningNetwork(coinName).middlewarePubKey, 'hex');
+  const userAuthHdNode = utxolib.bip32.fromBase58(userXprv);
+  return sdkcore.getSharedSecret(userAuthHdNode, publicKey);
+}

modules/abstract-lightning/test/unit/lightning/lightningUtils.ts

@@ -13,6 +13,7 @@ import {
   createWatchOnly,
   addIPCaveatToMacaroon,
   deriveLightningServiceSharedSecret,
+  deriveMiddlewareSharedSecret,
 } from '../../../src/lightning';
 
 import * as sdkcore from '@bitgo/sdk-core';
@@ -99,4 +100,19 @@ describe('lightning utils', function () {
 
     assert.deepStrictEqual(secret, expectedSecret);
   });
+
+  it(`deriveMiddlewareSharedSecret`, function () {
+    const userAuthXprv =
+      'xprv9s21ZrQH143K4NPkV8riiTnFf72MRyQDVHMmmpekGF1w5QkS2MfTei9KXYvrZVMop4zQ4arnzSF7TRp3Cy73AWaDdADiYMCi5qpYW1bUa5m';
+    const middlewarePubKey = getStaticsLightningNetwork('tlnbtc').middlewarePubKey;
+
+    const expectedSecret = sdkcore.getSharedSecret(
+      utxolib.bip32.fromBase58(userAuthXprv),
+      Buffer.from(middlewarePubKey, 'hex')
+    );
+
+    const secret = deriveMiddlewareSharedSecret('tlnbtc', userAuthXprv);
+
+    assert.deepStrictEqual(secret, expectedSecret);
+  });
 });

modules/statics/src/networks.ts

@@ -25,6 +25,11 @@ export interface LightningNetwork extends UtxoNetwork {
    * by enabling the creation of a shared secret for encryption and decryption of data.
    */
   lightningServicePubKey: string;
+  /**
+   * The public key of the middleware service, used for deriving the shared Elliptic Curve Diffie-Hellman (ECDH) secret
+   * between the user's extended private key and the middleware service.
+   */
+  middlewarePubKey: string;
 }
 
 export interface AdaNetwork extends BaseNetwork {
@@ -321,6 +326,8 @@ class LightningBitcoin extends Mainnet implements LightningNetwork {
   utxolibName = 'bitcoin';
   explorerUrl = 'https://mempool.space/lightning';
   lightningServicePubKey = '0338508686f978ceffd7ce05404041b1a5b4f75a39bc92a6d355240ccc081f763e';
+  // TODO - BTC-2202
+  middlewarePubKey = '';
 }
 
 class LightningBitcoinTestnet extends Testnet implements LightningNetwork {
@@ -329,6 +336,7 @@ class LightningBitcoinTestnet extends Testnet implements LightningNetwork {
   utxolibName = 'testnet';
   explorerUrl = 'https://mempool.space/testnet/lightning';
   lightningServicePubKey = '024055021db1e7f019ebb783ab0b0810c21a819207d4cb1ec4a6e2150ac07f1482';
+  middlewarePubKey = '027cb3bc6b49fc385d282b42a7be232a94ffcbaffc7818b603b17722582bbf539b';
 }
 
 class Bitcoin extends Mainnet implements UtxoNetwork {