Hooking a Method in an Android Game Tutorial (With Examples)

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In today’s tutorial, I will show you how you can hook a method when modding an Android game, hooking can be useful in many cases such as making your own cheat, changing the game data to have your desired outcome, debug it and more. Hooking can also help you unlink a shared function or a method.

Many times while modding a game you may have come across a method which was shared with the enemies, such as damage, health, etc. Hooking can help you unlink those methods.

Prerequisites

  • Rooted Android Device: Many modding tools require root access.
  • Frida: A dynamic instrumentation toolkit for developers, reverse-engineers, and security researchers.
  • ADB (Android Debug Bridge): To connect your device to your computer.
  • Basic knowledge of programming: Understanding of how to read and write simple code.
  • Target Game: An Android game installed on your device where you want to modify a value, like health.

Step 1: Setting Up Your Environment

  1. Install ADB: Download and install ADB from the Android developer website.
  2. Install Frida: Follow the instructions on the Frida website to install it on your computer. You will need both the Frida server for Android and the Frida tools for your computer.

Step 2: Preparing Your Device

  1. Root Your Device: This process varies depending on your device. Look up specific instructions for your model.
  2. Enable USB Debugging: Go to Settings > Developer Options > USB Debugging and enable it.

Step 3: Setting Up Frida on Your Device

  1. Download Frida Server: Download the appropriate Frida server version for your device’s architecture (ARM, ARM64, etc.) from the Frida releases page.
  2. Push Frida Server to Your Device: 
    adb push frida-server /data/local/tmp/
  3. Change Permissions and Start Frida Server: 
    adb shell
su
chmod 755 /data/local/tmp/frida-server
/data/local/tmp/frida-server &

Step 4: Writing Your Hook Script

  1. Identify the Method to Hook: Use tools like IDA Pro or Ghidra to reverse-engineer the game APK and find the method responsible for setting the health value.
  2. Write the Hook Script: Create a JavaScript file, let’s call it hook.js. 
    Java.perform(function () {
    var GameClass = Java.use('com.example.game.GameClass'); // Replace with actual class name
    GameClass.setHealth.implementation = function (newHealth) {
        console.log('Original Health:', newHealth);
        var modifiedHealth = 9999; // Modify health value
        console.log('Modified Health:', modifiedHealth);
        return this.setHealth(modifiedHealth);
    };
});

Step 5: Running the Hook Script

  1. Connect Your Device via ADB: 
    adb devices
  2. Start the Target Game: Launch the game on your device.
  3. Run Frida Script: 
    frida -U -f com.example.game -l hook.js --no-pause

Explanation

  • Java.perform: Ensures the script runs in the context of the Java VM.
  • Java.use(‘com.example.game.GameClass’): Replace 'com.example.game.GameClass' with the actual class name you found using reverse engineering.
  • GameClass.setHealth.implementation: Hooks the setHealth method.
  • newHealth: The original health value passed to the method.
  • modifiedHealth: The new health value you want to set.

Other Hooking Examples

Basic Example: Hooking a Simple Method (Score Increment)

Java.perform(function () {
    var GameClass = Java.use('com.example.game.GameClass'); // Replace with actual class name
    GameClass.incrementScore.implementation = function (points) {
        console.log('Original Points:', points);
        var modifiedPoints = points * 2; // Double the points
        console.log('Modified Points:', modifiedPoints);
        return this.incrementScore(modifiedPoints);
    };
});

In this example, we hook the incrementScore method to double the points awarded.

Intermediate Example: Modifying Ammo Count

Java.perform(function () {
    var PlayerClass = Java.use('com.example.game.Player'); // Replace with actual class name
    PlayerClass.setAmmoCount.implementation = function (ammo) {
        console.log('Original Ammo:', ammo);
        var unlimitedAmmo = 9999; // Set ammo to 9999
        console.log('Modified Ammo:', unlimitedAmmo);
        return this.setAmmoCount(unlimitedAmmo);
    };
});

Here, we hook the setAmmoCount method to give the player unlimited ammo.

Complex Example: Modifying In-Game Currency

Java.perform(function () {
    var CurrencyManager = Java.use('com.example.game.CurrencyManager'); // Replace with actual class name
    CurrencyManager.updateCurrency.implementation = function (currencyType, amount) {
        console.log('Original Currency Type:', currencyType, 'Original Amount:', amount);
        if (currencyType.equals("gold")) {
            var modifiedAmount = amount + 1000; // Add 1000 gold
            console.log('Modified Amount:', modifiedAmount);
            return this.updateCurrency(currencyType, modifiedAmount);
        } else if (currencyType.equals("gems")) {
            var modifiedGems = amount * 2; // Double the gems
            console.log('Modified Gems:', modifiedGems);
            return this.updateCurrency(currencyType, modifiedGems);
        } else {
            return this.updateCurrency(currencyType, amount);
        }
    };
});

In this example, we hook the updateCurrency method to add specific modifications to different types of in-game currency.

Example: Unlinking Shared Methods for Player and Enemies

Java.perform(function () {
    var GameCharacter = Java.use('com.example.game.GameCharacter'); // Replace with actual class name
    GameCharacter.setHealth.implementation = function (newHealth) {
        if (this.isPlayer()) { // Assuming there's a method to check if the character is the player
            console.log('Player Health:', newHealth);
            var modifiedHealth = 9999; // Modify player health
            console.log('Modified Player Health:', modifiedHealth);
            return this.setHealth(modifiedHealth);
        } else {
            console.log('Enemy Health:', newHealth);
            // Optionally modify enemy health
            return this.setHealth(newHealth);
        }
    };
});

In this example, we check if the method is being called for the player using this.isPlayer(). If it’s for the player, we modify the health value; otherwise, we handle the enemy’s health differently.

Detailed Explanation

  • Java.perform: Ensures the script runs in the context of the Java VM.
  • Java.use(‘com.example.game.GameCharacter’): Replace 'com.example.game.GameCharacter' with the actual class name found using reverse engineering tools like IDA Pro or Ghidra.
  • GameCharacter.setHealth.implementation: Hooks the setHealth method.
  • this.isPlayer(): A hypothetical method to check if the character is the player. This needs to be replaced with the actual logic to differentiate between the player and enemies in the game.
  • Modified Health: Apply different health values for the player and enemies as needed.

Addtional Tips

  • Ensure Correct Identification: Make sure you have a reliable way to differentiate between the player and enemies. This might involve additional reverse engineering to understand the game’s logic.
  • Testing: Test thoroughly to ensure that the changes do not introduce bugs or crashes.

Important Notes

  • Legal and Ethical Considerations: Modding games can violate terms of service and lead to bans. Always ensure you have permission to modify the game.
  • Learning and Practice: Practice on simple, non-critical applications to understand the process before attempting to mod more complex games.
  • Community and Support: Join forums and communities for help and support.

This tutorial provides a basic example of how to hook a method in an Android game to modify the health value. The actual class names and method names will vary based on the game you are trying to mod. Happy modding!

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