Crackme RE Challenge

01. Introduction

Please install the given Android APK into your Android emulator. Run the app. You need a secret code to start the app. What is the secret code?

Your goal is to analyze the apk file and find the valid password.

APK File:

Crackme.zipDropbox

02. Analysis

Install the apk file on the android emulator:

adb install CrackMe.apk

Start the application and enter a password:

Let's analyse the code by using jadx-gui

In the MainActiviy class there is a string called secret_code

Later we can see that a base64 encoding is taking place. The input will be encoded with base64 and then be compared with the base64 encoded value of secret_code.

If the input matches I’ll get the message "Congratulations! You found the secret code." If not "Sorry incorrect, try again." will be displayed.

Let's try to decode the secret_code string:

echo MDE5MjgzNzQ2NTAw | base64 -d

Let's try to enter the password:

Challenge solved 👍