feat: implement resource index decryption

- Add `cipher` utility for resource index decryption/encryption
- Automatically decrypt `index_initial.json` and `index_main.json` during archiving
- pages: Update `ResourcesTab` to display links to decrypted versions of index files
- Update README to reflect that some raw data is now decrypted

src/cmds/archive.ts

@@ -5,6 +5,7 @@ import PQueue from 'p-queue';
 import semver from 'semver';
 import apiUtils from '../utils/api/index.js';
 import argvUtils from '../utils/argv.js';
+import cipher from '../utils/cipher.js';
 import appConfig from '../utils/config.js';
 import logger from '../utils/logger.js';
 import mathUtils from '../utils/math.js';
@@ -487,6 +488,26 @@ async function fetchAndSaveAllGameResRawData(gameTargets: GameTarget[]) {
   for (const url of webAssetUrls) addToQueue(url);
 
   await networkQueue.onIdle();
+
+  // res index decryption
+  for (const url of resourceUrls) {
+    const urlObj = new URL(url);
+    urlObj.search = '';
+    if (['index_initial.json', 'index_main.json'].includes(urlObj.pathname.split('/').pop()!) === false) continue;
+    const localPath = path.join(
+      argvUtils.getArgv()['outputDir'],
+      'raw',
+      urlObj.hostname,
+      ...urlObj.pathname.split('/').filter(Boolean),
+    );
+    const localPathDec = localPath.replace(/\.json$/, '_dec.json');
+    if (!(await Bun.file(localPathDec).exists()) && (await Bun.file(localPath).exists())) {
+      const encBytes = new Uint8Array(Buffer.from(await Bun.file(localPath).text(), 'base64'));
+      const decBytes = cipher.decryptResIndex(encBytes, appConfig.cipher.akEndfield.resIndexKey);
+      await Bun.write(localPathDec, decBytes);
+    }
+  }
+
   logger.info(`Fetched raw game resources: ${wroteFiles.length} files`);
 }
 

src/utils/cipher.ts

@@ -0,0 +1,28 @@
+function decryptResIndex(encData: Uint8Array, key: string): Uint8Array {
+  const keyBytes = Buffer.from(key, 'utf-8');
+  const keyLength = keyBytes.length;
+  const result = new Uint8Array(encData.length);
+  for (let i = 0; i < encData.length; i++) {
+    const encByte = encData[i]!;
+    const keyByte = keyBytes[i % keyLength]!;
+    result[i] = (encByte - keyByte + 256) % 256;
+  }
+  return result;
+}
+
+function encryptResIndex(plainData: Uint8Array, key: string): Uint8Array {
+  const keyBytes = Buffer.from(key, 'utf-8');
+  const keyLength = keyBytes.length;
+  const result = new Uint8Array(plainData.length);
+  for (let i = 0; i < plainData.length; i++) {
+    const plainByte = plainData[i]!;
+    const keyByte = keyBytes[i % keyLength]!;
+    result[i] = (plainByte + keyByte) % 256;
+  }
+  return result;
+}
+
+export default {
+  decryptResIndex,
+  encryptResIndex,
+};

src/utils/config.ts

@@ -12,6 +12,11 @@ type AllRequired<T> = Required<{
 
 type ConfigType = AllRequired<
   Freeze<{
+    cipher: {
+      akEndfield: {
+        resIndexKey: string;
+      };
+    };
     network: {
       api: {
         akEndfield: {
@@ -69,6 +74,11 @@ type ConfigType = AllRequired<
 >;
 
 const initialConfig: ConfigType = {
+  cipher: {
+    akEndfield: {
+      resIndexKey: 'Assets/Beyond/DynamicAssets/Gameplay/UI/Fonts/', // via reversing
+    },
+  },
   network: {
     api: {
       akEndfield: {