Chapter 1: Basics of Reverse Engineering – Understanding the Structure of Mobile Apps

All of us use cell phones in our daily lives now, and their usage has grown to such a crucial level that people frequently name cell phones as one of the three things you can't live without, after food and water. Cell phones handle almost every task, from managing funds in bank accounts and investments to travel bookings, shopping, and health appointments.

To perform these tasks, cell phones have mobile apps. These apps handle a majority of your data and help you perform tasks.

As these modern mobile apps handle sensitive user information, perform critical tasks, and provide access to a huge array of resources on the internet, the security of the data being handled and the operations performed on it also need to be improved.

A mobile application penetration tester tests the security of mobile applications in order to find vulnerabilities. To find the vulnerabilities, the tester is required to understand the internal working and logics of the application. These details can be found in the source code of the application. However, the penetration testers do not always have the source code to hand, as in the case of a black-box penetration test. During a black-box penetration test, all that the penetration tester has is the application package, that is, the Android Application Package (APK) or iOS App Store Package (IPA) file. In such a case, to understand the working of the app, they need to unpack the application package and get the source code.

Reverse engineering is the technique of dismantling an object to study its internal designs, code, logic, and so on. Reverse engineering mobile applications is the process of disassembling/dismantling an app to reveal its code and internal logic, components, and so on.

In this chapter, we're going to cover the following main topics:

• Reverse engineering fundamentals
• Android application fundamentals
• iOS application fundamentals

We will learn about the basics of reverse engineering and how mobile applications are built. These fundamentals are important to understand before we can jump into the actual task of reverse engineering modern apps.