Reverse engineering fundamentals

Let's first understand the fundamentals of reverse engineering, why it is needed, and what steps are involved.

As mentioned earlier in this chapter, reverse engineering is the technique of dismantling an object to study its internal designs, code, and logic.

When a developer builds a mobile app, they choose a programming language (according to the targeted platform – Android, iOS, or both), write the code for the functionalities they want, and add resources such as images, certificates, and so on. Then the code is compiled to create the application package.

While reverse engineering the same app, the reverse engineer dismantles the application package to the components and code.

Some of the frequently used terms in reverse engineering are the following:

• Decompilation: This is the process of translating a file from a low-level language to a higher level language. The tool used to perform decompilation is called a decompiler. A decompiler takes a binary program file and changes this program into a higher-level structured language. The following diagram illustrates the decompilation process:

Figure 1.1 – Diagram of the decompilation process

• Disassembling: This is the process of transforming machine code (in an object code binary file) into a human-readable mnemonic representation called assembly language. The tool used to perform disassembly is called a disassembler as it does the opposite of what an assembler does. The following diagram illustrates the disassembly process:

Figure 1.2 – Diagram of the disassembly process

A simple binary disassembled in a disassembling tool, Hopper, looks as follows:

Figure 1.3 – Disassembled binary in Hopper

• Debugging: This is a technique that allows the user to view and modify the state of a program at runtime. The following diagram illustrates the debugging process:

Figure 1.4 – Diagram of the debugging process

Understanding the different methodologies and approaches used in reverse engineering is very important. We will be using all these concepts in further chapters of this book.

Now that we have seen the fundamentals of reverse engineering, let's explore how mobile applications, that is, Android and iOS apps, are developed. We will now be looking into the components, structure, and concepts behind the mobile application fundamentals.