From 23b3ce36b48a8b43dc2bdf5890594df050d50796 Mon Sep 17 00:00:00 2001
From: Benjamin Smith <bh2smith@users.noreply.github.com>
Date: Fri, 15 Nov 2024 14:55:12 +0100
Subject: [PATCH] Root Public Key as SetupConfig (#148)

---
 src/index.ts       |  4 +++-
 src/mpcContract.ts | 12 ++++++++----
 src/utils/kdf.ts   |  4 ++--
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 97b7138..b890ff7 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -27,6 +27,7 @@ type KeyPairString = `ed25519:${string}` | `secp256k1:${string}`;
  * @property {NearConfig} [network] - (Optional) The NEAR network configuration.
  * @property {string} [privateKey] - (Optional) The private key for the account.
  * @property {string} [derivationPath] - (Optional) The derivation path for the Ethereum account. Defaults to "ethereum,1".
+ * @property {string} [rootPublicKey] - (Optional) The root public key for the account. If not available it will be fetched from the MPC contract.
  */
 export interface SetupConfig {
   accountId: string;
@@ -34,6 +35,7 @@ export interface SetupConfig {
   network?: NearConfig;
   privateKey?: string;
   derivationPath?: string;
+  rootPublicKey?: string;
 }
 
 /**
@@ -79,7 +81,7 @@ export async function setupAdapter(args: SetupConfig): Promise<NearEthAdapter> {
     throw error;
   }
   return NearEthAdapter.fromConfig({
-    mpcContract: new MpcContract(account, mpcContractId),
+    mpcContract: new MpcContract(account, mpcContractId, args.rootPublicKey),
     derivationPath: derivationPath,
   });
 }
diff --git a/src/mpcContract.ts b/src/mpcContract.ts
index b264c54..f8de388 100644
--- a/src/mpcContract.ts
+++ b/src/mpcContract.ts
@@ -44,11 +44,13 @@ interface MpcContractInterface extends Contract {
  * located in: https://github.com/near/mpc-recovery
  */
 export class MpcContract implements IMpcContract {
+  rootPublicKey: string | undefined;
   contract: MpcContractInterface;
   connectedAccount: Account;
 
-  constructor(account: Account, contractId: string) {
+  constructor(account: Account, contractId: string, rootPublicKey?: string) {
     this.connectedAccount = account;
+    this.rootPublicKey = rootPublicKey;
 
     this.contract = new Contract(account.connection, contractId, {
       changeMethods: ["sign"],
@@ -66,10 +68,12 @@ export class MpcContract implements IMpcContract {
   }
 
   deriveEthAddress = async (derivationPath: string): Promise<Address> => {
-    const rootPublicKey = await this.contract.public_key();
+    if (!this.rootPublicKey) {
+      this.rootPublicKey = await this.contract.public_key();
+    }
 
-    const publicKey = await deriveChildPublicKey(
-      najPublicKeyStrToUncompressedHexPoint(rootPublicKey),
+    const publicKey = deriveChildPublicKey(
+      najPublicKeyStrToUncompressedHexPoint(this.rootPublicKey),
       this.connectedAccount.accountId,
       derivationPath
     );
diff --git a/src/utils/kdf.ts b/src/utils/kdf.ts
index e2b6529..e4d43eb 100644
--- a/src/utils/kdf.ts
+++ b/src/utils/kdf.ts
@@ -10,11 +10,11 @@ export function najPublicKeyStrToUncompressedHexPoint(
   return "04" + Buffer.from(decodedKey).toString("hex");
 }
 
-export async function deriveChildPublicKey(
+export function deriveChildPublicKey(
   parentUncompressedPublicKeyHex: string,
   signerId: string,
   path: string = ""
-): Promise<string> {
+): string {
   const ec = new EC("secp256k1");
   const scalarHex = sha3_256(
     `near-mpc-recovery v0.1.0 epsilon derivation:${signerId},${path}`