From 80dbeeb5459519e07ff8b5ccd10255e98e76d70b Mon Sep 17 00:00:00 2001
From: daydreamer-json <atarakima1@icloud.com>
Date: Mon, 30 Mar 2026 17:21:08 +0900
Subject: [PATCH] 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
---
 README.md                                     |  2 +-
 pages-v2/src/components/tabs/ResourcesTab.tsx | 19 ++++++++++---
 src/cmds/archive.ts                           | 21 ++++++++++++++
 src/utils/cipher.ts                           | 28 +++++++++++++++++++
 src/utils/config.ts                           | 10 +++++++
 5 files changed, 75 insertions(+), 5 deletions(-)
 create mode 100644 src/utils/cipher.ts

diff --git a/README.md b/README.md
index b5bbda3..45aeb6f 100644
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@ The APIs currently being monitored are as follows:
 - Raw
   - Game resource json (index, patch)
 
-Currently, raw data is provided as-is without modification. It is also not decrypted.
+Most of the raw data is provided as-is, without any modifications. Some data (`index_*.json`) has been decrypted.
 
 ## Download Library
 
diff --git a/pages-v2/src/components/tabs/ResourcesTab.tsx b/pages-v2/src/components/tabs/ResourcesTab.tsx
index 6b688a4..a13ca8b 100644
--- a/pages-v2/src/components/tabs/ResourcesTab.tsx
+++ b/pages-v2/src/components/tabs/ResourcesTab.tsx
@@ -140,7 +140,7 @@ function processRawData(rawData: StoredData<IApiEndfield.LauncherLatestGameResou
   });
 }
 
-const ResourceLink = ({ basePath, file }: { basePath: string; file: string }) => {
+const ResourceLink = ({ basePath, file, isDecExist }: { basePath: string; file: string; isDecExist: boolean }) => {
   const fullPath = `${basePath}/${file}`;
   return (
     <>
@@ -151,6 +151,17 @@ const ResourceLink = ({ basePath, file }: { basePath: string; file: string }) =>
       <a href={getMirrorUrl(fullPath)} target='_blank' rel='noreferrer'>
         Mirror
       </a>
+      {isDecExist ? (
+        <>
+          {' '}
+          /{' '}
+          <a href={getMirrorUrl(fullPath).replace(/\.json$/, '_dec.json')} target='_blank' rel='noreferrer'>
+            Dec
+          </a>
+        </>
+      ) : (
+        ''
+      )}
     </>
   );
 };
@@ -186,13 +197,13 @@ const ResourceTable = ({ groups }: { groups: ResourceGroup[] }) => (
             <td>{group.versions.join(', ')}</td>
             <td className='text-center'>{group.isKick ? '✅' : ''}</td>
             <td>
-              <ResourceLink basePath={group.initialRes.path} file='index_initial.json' />
+              <ResourceLink basePath={group.initialRes.path} file='index_initial.json' isDecExist={true} />
             </td>
             <td>
-              <ResourceLink basePath={group.mainRes.path} file='index_main.json' />
+              <ResourceLink basePath={group.mainRes.path} file='index_main.json' isDecExist={true} />
             </td>
             <td>
-              <ResourceLink basePath={group.mainRes.path} file='patch.json' />
+              <ResourceLink basePath={group.mainRes.path} file='patch.json' isDecExist={false} />
             </td>
           </tr>
         ))}
diff --git a/src/cmds/archive.ts b/src/cmds/archive.ts
index 7f3446c..c2cd12c 100644
--- a/src/cmds/archive.ts
+++ b/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`);
 }
 
diff --git a/src/utils/cipher.ts b/src/utils/cipher.ts
new file mode 100644
index 0000000..f75c1e3
--- /dev/null
+++ b/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,
+};
diff --git a/src/utils/config.ts b/src/utils/config.ts
index a06a67e..a4f27f6 100644
--- a/src/utils/config.ts
+++ b/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: {