iOS SelRef Obfuscation, Anti-Reversing in iOS Apps
This Knowledge Base article describes how to use Appdome’s AI/ML in your CI/CD pipeline to continuously deliver plugins that Add SelRef Obfuscation in iOS apps.
What is Objective-C SelRef?
iOS applications run on Apple mobile devices within the Objective-C runtime. Because the runtime does not work with method names, when building iOS apps the class’s method name is converted into a selector that represents this method, and therefore acts as the link between the method name and its implementation in the app. This selector is referred to as a “SelRef” (Selector Reference) in the compiled binary. Using selectors has many benefits, such as reducing app size by storing only one ASCII representation of all methods that share the same name, as well as the ability to extend and override a specific method’s logic.
Why do developers need to obfuscate SelRefs in iOS apps?
Attackers use SelRef during static analysis and reverse engineering to gain a deep understanding of the inner workings of an iOS app. For example, determining which method is being called within a function is only possible by resolving the selRef being used to the method it is associated to. Furthermore, attackers can perform the opposite conversion, going from method names to it’s SelRef, to find all calls to method in question by finding all references to the SelRef. Obfuscating SelRef in the application binary prevents the attacker from performing these conversions, thereby significantly limiting the risk of reverse engineering.
Prerequisites for Using Appdome's Obj-C SelRef Obfuscation Plugins:
To use Appdome’s mobile app security build system to Add SelRef Obfuscation , you’ll need:
- Appdome account (create a free Appdome account here)
- A license for Obj-C SelRef Obfuscation
- Mobile App (.ipa for iOS)
- Signing Credentials (see Signing Secure Android apps and Signing Secure iOS apps)
How to Implement Add SelRef Obfuscation in iOS Apps Using Appdome
On Appdome, follow these 3 simple steps to create self-defending iOS Apps that Add SelRef Obfuscation without an SDK or gateway:
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Designate the Mobile App to be protected.
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Upload an app via the Appdome Mobile Defense platform GUI or via Appdome’s DEV-API or CI/CD Plugins.
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iOS Formats: .ipa
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Obj-C SelRef Obfuscation is compatible with: Obj-C, Java, Swift, Flutter, React Native, Unity, Xamarin, Cordova and other iOS apps.
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Select the defense: Obj-C SelRef Obfuscation.
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Follow the steps in Sections 2.2-2.2.2 of this article to add the Obj-C SelRef Obfuscation feature to your Fusion Set via the Appdome Console.
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When you select the Obj-C SelRef Obfuscation you'll notice that the Fusion Set you created in step 2.1 now bears the icon of the protection category that contains Obj-C SelRef Obfuscation.
Figure 2: Fusion Set that displays the newly added Obj-C SelRef Obfuscation protection
Note: Annotating the Fusion Set to identify the protection(s) selected is optional only (not mandatory). -
Open the Fusion Set Detail Summary by clicking the “...” symbol on the far-right corner of the Fusion Set. Copy the Fusion Set ID from the Fusion Set Detail Summary (as shown below):
Figure 3: Fusion Set Detail Summary
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Follow the instructions below to use the Fusion Set ID inside any standard mobile DevOps or CI/CD toolkit like Bitrise, Jenkins, Travis, Team City, Circle CI or other system:
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Refer to the Appdome API Reference Guide for API building instructions.
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Look for sample APIs in Appdome’s GitHub Repository.
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Create and name the Fusion Set (security template) that will contain the Obj-C SelRef Obfuscation feature as shown below:Figure 1: Fusion Set that will contain the Obj-C SelRef Obfuscation feature
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Add the Obj-C SelRef Obfuscation feature to your security template.
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Navigate to Build > Security tab > TOTALCode™ Obfuscation section in the Appdome Console.
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Toggle On > Obj-C SelRef Obfuscation.
Figure 4: Selecting Add SelRef Obfuscation
Note: The Appdome Platform displays the Mobile Operation Systems supported by each defense in real-time. For more details, see our OS Support Policy KB. -
Configure the User Experience Options for Obj-C SelRef Obfuscation:
With Threat-Events™ OFF, Appdome provides several user experience options for mobile brands and developers.- App Compromise Notification: Customize the pop-up or toast Appdome uses to notify the user when a threat is present while using the protected mobile app.
- Short message Option. This is available for mobile devices that allow a banner notification for security events.
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Localized Message Option. Allows Appdome users to support global languages in security notifications.
Figure 5: Default User Experience Options for Appdome’s SelRef Obfuscation
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Obj-C SelRef Obfuscation Threat Code™. Appdome uses AI/ML to generate a unique code each time Obj-C SelRef Obfuscation is triggered by an active threat on the mobile device. Use the code in Appdome Threat Resolution Center™ to help end users identify, find and resolve active threats on the personal mobile devices.
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Congratulations! The Obj-C SelRef Obfuscation protection is now added to the mobile app -
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Certify the Obj-C SelRef Obfuscation feature in iOS Apps
After building Obj-C SelRef Obfuscation, Appdome generates a Certified Secure™ certificate to guarantee that the Obj-C SelRef Obfuscation protection has been added and is protecting the app. To verify that the Obj-C SelRef Obfuscation protection has been added to the mobile app, locate the protection in the Certified Secure™ certificate as shown below:
Figure 6: Certified Secure™ certificate
Each Certified Secure™ certificate provides DevOps and DevSecOps organizations the entire workflow summary, audit trail of each build, and proof of protection that Obj-C SelRef Obfuscation has been added to each iOS app. Certified Secure provides instant and in-line DevSecOps compliance certification that Obj-C SelRef Obfuscation and other mobile app security features are in each build of the mobile app.
Using Threat-Events™ for SelRef Obfuscation Intelligence and Control in iOS Apps
Appdome Threat-Events™ provides consumable in-app mobile app attack intelligence and defense control when SelRef Obfuscation is detected. To consume and use Threat-Events™ for SelRef Obfuscation in iOS Apps, use AddObserverForName in Notification Center, and the code samples for Threat-Events™ for SelRef Obfuscation shown below.
The specifications and options for Threat-Events™ for SelRef Obfuscation are:
Threat-Event™ Elements | Add SelRef Obfuscation Method Detail |
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Appdome Feature Name | Obj-C SelRef Obfuscation |
Threat-Event Mode | |
OFF, IN-APP DEFENSE | Appdome detects, defends and notifies user (standard OS dialog) using customizable messaging. |
ON, IN-APP DETECTION | Appdome detects the attack or threat and passes the event in a standard format to the app for processing (app chooses how and when to enforce). |
ON, IN-APP DEFENSE | Uses Appdome Enforce mode for any attack or threat and passes the event in a standard format to the app for processing (gather intel on attacks and threats without losing any protection). |
Certified Secure™ Threat Event Check | x |
Visible in ThreatScope™ | x |
Developer Parameters for Adding SelRef Obfuscation Threat-Event™ | |
Threat-Event NAME | |
Threat-Event DATA | reasonData |
Threat-Event CODE | reasonCode |
Threat-Event REF | |
Threat-Event SCORE | |
currentThreatEventScore | Current Threat-Event score |
threatEventsScore | Total Threat-events score |
Threat-Event Context Keys | |
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message | Message displayed for the user on event |
failSafeEnforce | Timed enforcement against the identified threat |
externalID | The external ID of the event which can be listened via Threat Events |
osVersion | OS version of the current device |
deviceModel | Current device model |
deviceManufacturer | The manufacturer of the current device |
fusedAppToken | The task ID of the Appdome fusion of the currently running app |
kernelInfo | Info about the kernel: system name, node name, release, version and machine. |
deviceID | Current device ID |
reasonCode | Reason code of the occurred event |
buildDate | Appdome fusion date of the current application |
devicePlatform | OS name of the current device |
updatedOSVersion | Is the OS version up to date |
timeZone | Time zone |
deviceFaceDown | Is the device face down |
locationLong | Location longitude conditioned by location permission |
locationLat | Location latitude conditioned by location permission |
locationState | Location state conditioned by location permission |
wifiSsid | Wifi SSID |
wifiSsidPermissionStatus | Wifi SSID permission status |
threatCode | The last six characters of the threat code specify the OS, allowing the Threat Resolution Center to address the attack on the affected device. |
With Threat-Events™ enabled (turned ON), iOS developers can get detailed attack intelligence and granular defense control in iOS applications and create amazing user experiences for all mobile end users when SelRef Obfuscation is detected.
The following is a code sample for native iOS apps, which uses all values in the specification above for Obj-C SelRef Obfuscation:
Important! Replace all placeholder instances of <Context Key> with the specific name of your threat event context key across all language examples. This is crucial to ensure your code functions correctly with the intended event data. For example, The <Context Key> could be the message, externalID, OS Version, reason code, etc.
x
let center = NotificationCenter.default
center.addObserver(forName: Notification.Name(""), object: nil, queue: nil) { (note) in
guard let usrInf = note.userInfo else {
return
}
let message = usrInf["message"]; // Message shown to the user
let reasonData = usrInf["reasonData"]; // Threat detection cause
let reasonCode = usrInf["reasonCode"]; // Event reason code
// Current threat event score
let currentThreatEventScore = usrInf["currentThreatEventScore"];
// Total threat events score
let threatEventsScore = usrInf["threatEventsScore"];
// Replace '<Context Key>' with your specific event context key
// let variable = usrInf["<Context Key>"];
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
}
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[[NSNotificationCenter defaultCenter] addObserverForName: @"" object:nil queue:nil usingBlock:^(NSNotification *org_note) {
__block NSNotification *note = org_note;
dispatch_async(dispatch_get_main_queue(), ^(void) {
// Message shown to the user
NSString *message = [[note userInfo] objectForKey:@"message"];
// Threat detection cause
NSString *reasonData = [[note userInfo] objectForKey:@"reasonData"];
// Event reason code
NSString *reasonCode = [[note userInfo] objectForKey:@"reasonCode"];
// Current threat event score
NSString *currentThreatEventScore = [[note userInfo] objectForKey:@"currentThreatEventScore"];
// Total threat events score
NSString *threatEventsScore = [[note userInfo] objectForKey:@"threatEventsScore"];
// Replace '<Context Key>' with your specific event context key
// NSString *variable = [[note userInfo] objectForKey:@"<Context Key>"];
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
});
}];
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const { ADDevEvents } = NativeModules;
const aDDevEvents = new NativeEventEmitter(ADDevEvents);
function registerToDevEvent(action, callback) {
NativeModules.ADDevEvents.registerForDevEvent(action);
aDDevEvents.addListener(action, callback);
}
export function registerToAllEvents() {
registerToDevEvent(
"",
(userinfo) => Alert.alert(JSON.stringify(userinfo))
var message = userinfo["message"] // Message shown to the user
var reasonData = userinfo["reasonData"] // Threat detection cause
var reasonCode = userinfo["reasonCode"] // Event reason code
// Current threat event score
var currentThreatEventScore = userinfo["currentThreatEventScore"]
// Total threat events score
var threatEventsScore = userinfo["threatEventsScore"]
// Replace '<Context Key>' with your specific event context key
// var variable = userinfo["<Context Key>"]
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
);
}
x
RegisterReceiver(new ThreatEventReceiver(), new IntentFilter(""));
class ThreatEventReceiver : BroadcastReceiver
{
public override void OnReceive(Context context, Intent intent)
{
// Message shown to the user
String message = intent.GetStringExtra("message");
// Threat detection cause
String reasonData = intent.GetStringExtra("reasonData");
// Event reason code
String reasonCode = intent.GetStringExtra("reasonCode");
// Current threat event score
String currentThreatEventScore = intent.GetStringExtra("currentThreatEventScore");
// Total threat events score
String threatEventsScore = intent.GetStringExtra("threatEventsScore");
// Replace '<Context Key>' with your specific event context key
// String variable = intent.GetStringExtra("<Context Key>");
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
}
}
x
NSNotificationCenter.DefaultCenter.AddObserver(
(NSString)"", // Threat-Event Identifier
delegate (NSNotification notification)
{
// Message shown to the user
var message = notification.UserInfo.ObjectForKey("message");
// Threat detection cause
var reasonData = notification.UserInfo.ObjectForKey("reasonData");
// Event reason code
var reasonCode = notification.UserInfo.ObjectForKey("reasonCode");
// Current threat event score
var currentThreatEventScore = notification.UserInfo.ObjectForKey("currentThreatEventScore");
// Total threat events score
var threatEventsScore = notification.UserInfo.ObjectForKey("threatEventsScore");
// Replace '<Context Key>' with your specific event context key
// var variable = notification.UserInfo.ObjectForKey("<Context Keys>");
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
}
);
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window.broadcaster.addEventListener("", function(userInfo) {
var message = userInfo.message // Message shown to the user
var reasonData = userInfo.reasonData // Threat detection cause
var reasonCode = userInfo.reasonCode // Event reason code
// Current threat event score
var currentThreatEventScore = userInfo.currentThreatEventScore
// Total threat events score
var threatEventsScore = userInfo.threatEventsScore
// Replace '<Context Key>' with your specific event context key
// var variable = userInfo.<Context Keys>
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
});
x
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
class PlatformChannel extends StatefulWidget {
const PlatformChannel({super.key});
State<PlatformChannel> createState() => _PlatformChannelState();
}
class _PlatformChannelState extends State<PlatformChannel> {
// Replace with your EventChannel name
static const String _eventChannelName = "";
static const EventChannel _eventChannel = EventChannel(_eventChannelName);
void initState() {
super.initState();
_eventChannel.receiveBroadcastStream().listen(_onEvent, onError: _onError);
}
void _onEvent(Object? event) {
setState(() {
// Adapt this section based on your specific event data structure
var eventData = event as Map;
// Example: Accessing 'externalID' field from the event
var externalID = eventData['externalID'];
// Customize the rest of the fields based on your event structure
String message = eventData['message']; // Message shown to the user
String reasonData = eventData['reasonData']; // Threat detection cause
String reasonCode = eventData['reasonCode']; // Event reason code
// Current threat event score
String currentThreatEventScore = eventData['currentThreatEventScore'];
// Total threat events score
String threatEventsScore = eventData['threatEventsScore'];
// Replace '<Context Key>' with your specific event context key
// String variable = eventData['<Context Keys>'];
});
}
// Your logic goes here (Send data to Splunk/Dynatrace/Show Popup...)
}
Using Appdome, there are no development or coding prerequisites to build secured iOS Apps by using Obj-C SelRef Obfuscation. There is no SDK and no library to code or implement in the app and no gateway to deploy in your network. All protections are built into each app and the resulting app is self-defending and self-protecting.
Releasing and Publishing Mobile Apps with Obj-C SelRef Obfuscation
After successfully securing your app by using Appdome, there are several available options to complete your project, depending on your app lifecycle or workflow. These include:
- Customizing, Configuring & Branding Secure Mobile Apps.
- Deploying/Publishing Secure mobile apps to Public or Private app stores.
- Releasing Secured Android & iOS Apps built on Appdome.
Related Articles:
How Do I Learn More?
If you have any questions, please send them our way at support.appdome.com or via the chat window on the Appdome platform.
Thank you!
Thanks for visiting Appdome! Our mission is to secure every app on the planet by making mobile app security easy. We hope we’re living up to the mission with your project.