refactor: descramble n token algorithm instead of executing it directly for better security

lib/Constants.js

@@ -175,7 +175,14 @@ const formatVideoData = (data, context, desktop) => {
   return video_details;
 };
 
-const filters = (order) => { // TODO: Refactor this crazy thing
+
+const base64_alphabet = {
+  normal: 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'.split(''),
+  reverse: '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_'.split('')
+};
+
+const filters = (order) => {
+  // TODO: Refactor this with protobuf encoding
   switch (order) {
     case 'any,any,relevance':
       return 'EgIQAQ%3D%3D';
@@ -325,4 +332,4 @@ const filters = (order) => { // TODO: Refactor this crazy thing
   }
 };
 
-module.exports = { urls, oauth, oauth_reqopts, default_headers, innertube_request_opts, video_details_reqbody, stream_headers, formatVideoData, filters };
+module.exports = { urls, oauth, oauth_reqopts, default_headers, innertube_request_opts, video_details_reqbody, stream_headers, formatVideoData, base64_alphabet, filters };

lib/Innertube.js

@@ -5,6 +5,7 @@ const Stream = require('stream');
 const OAuth = require('./OAuth');
 const Utils = require('./Utils');
 const Player = require('./Player');
+const NToken = require('./NToken');
 const Actions = require('./Actions');
 const Livechat = require('./Livechat');
 const Constants = require('./Constants');
@@ -308,12 +309,12 @@ class Innertube extends EventEmitter {
         format.url = format.url || format.signatureCipher || format.cipher;
 
         if (format.signatureCipher || format.cipher) {
-          format.url = new SigDecipher(format.url, this.context.client.clientVersion, this.player.sig_decipher_sc, this.player.encodeN).decipher();
+          format.url = new SigDecipher(format.url, this.context.client.clientVersion, this.player).decipher();
         } else {
           const url_components = new URL(format.url);
           url_components.searchParams.set('cver', this.context.client.clientVersion);
           url_components.searchParams.set('ratebypass', 'yes');
-          url_components.searchParams.set('n', this.player.encodeN(url_components.searchParams.get('n')));
+          url_components.searchParams.set('n', new NToken(this.player.ntoken_sc).transform(url_components.searchParams.get('n')));
           format.url = url_components.toString();
         }
 

lib/Livechat.js

@@ -21,10 +21,10 @@ class Livechat extends EventEmitter {
 
     this.poll();
   }
-  
+
   enqueueActionGroup(group) {
     group.forEach((action) => {
-      if (!action.addChatItemAction) return; //TODO: handle different action types */
+      if (!action.addChatItemAction) return; //TODO: handle different action types 
       const message_content = action.addChatItemAction.item.liveChatTextMessageRenderer;
       if (!message_content) return;
 
@@ -38,7 +38,7 @@ class Livechat extends EventEmitter {
         timestamp: message_content.timestampUsec,
         id: message_content.id
       };
-      
+
       this.message_queue.push(message);
     });
   }
@@ -62,9 +62,9 @@ class Livechat extends EventEmitter {
       setTimeout(() => this.emit('chat-update', message), message.timestamp / 1000 - new Date().getTime());
       this.id_cache.push(message.id);
     });
-    
+
     this.message_queue = [];
-    
+
     data = { context: this.session.context, videoId: this.video_id };
     if (this.metadata_ctoken) data.continuation = this.metadata_ctoken;
 
@@ -81,23 +81,23 @@ class Livechat extends EventEmitter {
         short_view_count: metadata[0].updateViewershipAction.viewCount.videoViewCountRenderer.extraShortViewCount.simpleText
       }
     });
-    
+
     this.livechat_poller = setTimeout(async () => await this.poll(), this.poll_intervals_ms);
   }
-  
+
   async sendMessage(text) {
     const message = await Actions.livechat(this.session, 'live_chat/send_message', { text, channel_id: this.channel_id, video_id: this.video_id });
     if (!message.success) return message;
-   
+
     const deleteMessage = async () => {
       const menu = await Actions.livechat(this.session, 'live_chat/get_item_context_menu', { params: { params: message.data.actions[0].addChatItemAction.item.liveChatTextMessageRenderer.contextMenuEndpoint.liveChatItemContextMenuEndpoint.params, pbj: 1 } });
       if (!menu.success) return menu;
-      
+
       const chat_item_menu = menu.data.liveChatItemContextMenuSupportedRenderers.menuRenderer.items[0];
-      
+
       const cmd = await Actions.livechat(this.session, 'live_chat/moderate', { cmd_params: chat_item_menu.menuServiceItemRenderer.serviceEndpoint.moderateLiveChatEndpoint.params });
       if (!cmd.success) return cmd;
-     
+
       return { success: true, status_code: cmd.status_code };
     };
 
@@ -117,9 +117,9 @@ class Livechat extends EventEmitter {
       }
     };
   }
-  
+
   async blockUser(msg_params) {
-    /* TODO: Implement this */ 
+    /* TODO: Implement this */
     throw new Error('Not implemented');
   }
 

lib/NToken.js

@@ -0,0 +1,129 @@
+'use strict';
+
+const Utils = require('./Utils');
+const Constants = require('./Constants');
+
+class NToken {
+  constructor(raw_code) {
+    this.raw_code = raw_code;
+    this.null_placeholder_regex = /c\[(.*?)\]=c/g;
+    this.transformation_args_regex = /c\[(.*?)\]\((.+?)\)/g;
+  }
+
+  transform(n) {
+    let n_token = n.split('');
+    let transformations = this.getTransformationData(this.raw_code);
+
+    // Identifies the necessary transformation functions and emulates them accordingly.
+    transformations = transformations.map((el, i) => {
+      if (el != null && typeof el != 'number') {
+        const is_reverse_base64 = el.includes('case 65:');
+        if (el.includes('function(d){for(var')) {
+          el = (arr) => this.pushSplice(arr);
+        } else if (el.includes('d.push(e)')) {
+          el = (arr, item) => this.push(arr, item);
+        } else if (el.includes('d.reverse()')) {
+          el = (arr) => this.reverse(arr);
+        } else if (el.includes('d.length;d.splice(e,1)')) {
+          el = (arr, index) => this.spliceOnce(arr, index);
+        } else if (el.includes('d[0])[0])')) {
+          el = (arr, index) => this.spliceTwice(arr, index);
+        } else if (el.includes('reverse().forEach')) {
+          el = (arr, index) => this.spliceReverseUnshift(arr, index);
+        } else if (el.includes('f=d[0];d[0]')) {
+          el = (arr, index) => this.swapFirstItem(arr, index);
+        } else if (el.includes('unshift(d.pop())')) {
+          el = (arr, index) => this.unshiftPop(arr, index);
+        } else if (el.includes('switch')) {
+          el = (arr, e) => this.translateAB(arr, e, is_reverse_base64);
+        } else if (el === 'b') {
+          el = n_token;
+        }
+      }
+      return el;
+    });
+
+    // Fills the null placeholders with a copy of the transformations array.
+    let null_placeholder_positions = [...this.raw_code.matchAll(this.null_placeholder_regex)].map((item) => parseInt(item[1]));
+    null_placeholder_positions.forEach((pos) => transformations[pos] = transformations);
+
+    // Parses and emulates calls to functions of the transformations array.
+    let transformation_args = [...Utils.getStringBetweenStrings(this.raw_code.replace(/\n/g, ''), 'try{', '}catch').matchAll(this.transformation_args_regex)].map((params) => ({ index: params[1], params: params[2] }));
+    transformation_args.forEach((data) => {
+      const index = data.index;
+      const param_index = data.params.split(',').map((param) => param.match(/c\[(.*?)\]/)[1]);
+      transformations[index](transformations[param_index[0]], transformations[param_index[1]]);
+    });
+
+    return n_token.join('');
+  }
+
+  getTransformationData() {
+    let transformation_data = '[' + Utils.getStringBetweenStrings(this.raw_code, 'c=[', '];c') + ']';
+    transformation_data = transformation_data
+      .replace(/function\(d,e\)/g, '"function(d,e)')
+      .replace(/function\(d\)/g, '"function(d)')
+      .replace(/,b,/g, ',"b",')
+      .replace(/,b/g, ',"b"')
+      .replace(/b,/g, '"b",')
+      .replace(/b]/g, '"b"]')
+      .replace(/},/g, '}",')
+      .replace(/""/g, '')
+      .replace(/length]\)}"/g, 'length])}');
+
+    return JSON.parse(transformation_data);
+  }
+
+  translateAB(arr, e, is_reverse_base64) {
+    let characters = is_reverse_base64 && Constants.base64_alphabet.reverse || Constants.base64_alphabet.normal;
+    arr.forEach(function(char, index, loc) {
+      this.push(loc[index] = characters[(characters.indexOf(char) - characters.indexOf(this[index]) + 64) % characters.length]);
+    }, e.split(''));
+  }
+
+  unshiftPop(arr, index) {
+    index = (index % arr.length + arr.length) % arr.length;
+    for (; index--;) {
+      arr.unshift(arr.pop());
+    }
+  }
+
+  swapFirstItem(arr, index) {
+    let oldValue = arr[0];
+    index = (index % arr.length + arr.length) % arr.length;
+    arr[0] = arr[index];
+    arr[index] = oldValue;
+  }
+
+  spliceReverseUnshift(arr, index) {
+    index = (index % arr.length + arr.length) % arr.length;
+    arr.splice(-index).reverse().forEach(function(f) {
+      arr.unshift(f);
+    });
+  }
+
+  spliceOnce(arr, index) {
+    index = (index % arr.length + arr.length) % arr.length;
+    arr.splice(index, 1);
+  }
+
+  spliceTwice(arr, index) {
+    index = (index % arr.length + arr.length) % arr.length;
+    arr.splice(0, 1, arr.splice(index, 1, arr[0])[0]);
+  }
+
+  pushSplice(arr) {
+    for (let index = arr.length; index;)
+      arr.push(arr.splice(--index, 1)[0]);
+  }
+
+  push(arr, item) {
+    arr.push(item);
+  }
+
+  reverse(arr) {
+    arr.reverse();
+  }
+}
+
+module.exports = NToken;

lib/Player.js

@@ -36,8 +36,7 @@ class Player {
   }
 
   getNEncoder(data) {
-    const raw_code = 'var b=a.split("")' + Utils.getStringBetweenStrings(data, 'b=a.split("")', '}return b.join("")}') + '} return b.join("");';
-    this.encodeN = Utils.createFunction('a', raw_code);
+    this.ntoken_sc = 'var b=a.split("")' + Utils.getStringBetweenStrings(data, 'b=a.split("")', '}return b.join("")}') + '} return b.join("");';
   }
 }
 

lib/SigDecipher.js

@@ -1,13 +1,13 @@
 'use strict';
 
+const NToken = require('./NToken');
 const QueryString = require('querystring');
 
 class SigDecipher {
-  constructor(url, cver, func_code, encode_n) {
+  constructor(url, cver, player) {
     this.url = url;
     this.cver = cver;
-    this.func_code = func_code;
-    this.encode_n = encode_n;
+    this.player = player;
     this.func_regex = /(.{2}):function\(.*?\){(.*?)}/g;
     this.actions_regex = /;.{2}\.(.{2})\(.*?,(.*?)\)/g;
   }
@@ -33,7 +33,7 @@ class SigDecipher {
     let actions;
     let signature = args.s.split('');
 
-    while ((actions = this.actions_regex.exec(this.func_code)) !== null) {
+    while ((actions = this.actions_regex.exec(this.player.sig_decipher_sc)) !== null) {
       switch (actions[1]) {
         case functions[0]:
           reverse(signature, actions[2]);
@@ -49,10 +49,11 @@ class SigDecipher {
     }
 
     const url_components = new URL(args.url);
+    
     args.sp !== undefined ? url_components.searchParams.set(args.sp, signature.join('')) : url_components.searchParams.set('signature', signature.join(''));
     url_components.searchParams.set('cver', this.cver);
     url_components.searchParams.set('ratebypass', 'yes');
-    url_components.searchParams.set('n', this.encode_n(url_components.searchParams.get('n')));
+    url_components.searchParams.set('n', new NToken(this.player.ntoken_sc).transform(url_components.searchParams.get('n')));
     return url_components.toString();
   }
 
@@ -60,7 +61,7 @@ class SigDecipher {
     let func;
     let func_name = [];
 
-    while ((func = this.func_regex.exec(this.func_code)) !== null) {
+    while ((func = this.func_regex.exec(this.player.sig_decipher_sc)) !== null) {
       if (func[0].includes('reverse()')) {
         func_name[0] = func[1];
       } else if (func[0].includes('splice')) {

lib/Utils.js

@@ -37,13 +37,9 @@ function escapeStringRegexp(string) {
   return string.replace(/[|\\{}()[\]^$+*?.]/g, "\\$&").replace(/-/g, "\\x2d");
 }
 
-function createFunction(input, raw_code) { // I hate this
-  return new Function(input, raw_code);
-}
-
 function encodeNotificationPref(channel_id, index) {
   const youtube_proto = Proto(Fs.readFileSync(`${__dirname}/proto/youtube.proto`));
-  
+
   const buf = youtube_proto.NotificationPreferences.encode({
     channel_id,
     pref_id: {
@@ -52,24 +48,24 @@ function encodeNotificationPref(channel_id, index) {
     number_0: 0,
     number_1: 4
   });
-  
+
   return encodeURIComponent(Buffer.from(buf).toString('base64'));
 }
 
 function generateMessageParams(channel_id, video_id) {
   const youtube_proto = Proto(Fs.readFileSync(`${__dirname}/proto/youtube.proto`));
-  
+
   const buf = youtube_proto.LiveMessageParams.encode({
     params: {
       ids: {
-        channel_id, 
-        video_id 
+        channel_id,
+        video_id
       }
     },
     number_0: 1,
     number_1: 4
   });
-  
+
   return Buffer.from(encodeURIComponent(Buffer.from(buf).toString('base64'))).toString('base64');
 }
 
@@ -87,4 +83,4 @@ function generateCommentParams(video_id) {
   return encodeURIComponent(Buffer.from(buf).toString('base64'));
 }
 
-module.exports = { getRandomUserAgent, generateSidAuth, getStringBetweenStrings, createFunction, generateMessageParams, generateCommentParams, encodeNotificationPref };
+module.exports = { getRandomUserAgent, generateSidAuth, getStringBetweenStrings, generateMessageParams, generateCommentParams, encodeNotificationPref };