How to Reverse Engineer Software

If you’re like most developers, then you like to think about things logically. The beauty of code is that it’s based on pure logic. Any program can be deconstructed, replicated, and put back together if you’re willing to take the time to understand the logic behind it.

What is Software Reversing?

In essence, the software reverse engineering process is quite simple. You take a piece of existing software, and you break it down into the original source code. Once you have the source code, then you can understand everything that’s going on. With this knowledge, you can engineer new code.

Why Would Somebody Want to Reverse Engineer Software?

There are multiple reasons why somebody would want to know how to reverse engineer a software. The most outstanding reason is that developers are by nature curious beings. We don’t like the idea of a piece of software that we can’t understand or that’s above us. We like to be able to break down everything that’s going on into a simple code for our own understanding.

Reversing software and looking at the code of more advanced developers is the way that most of us learn to code in the first place. It teaches us new ways of thinking, gives us bright ideas, and allows us to better understand the principles of systems architecture.

The second reason somebody might wish to reverse engineer software is for debugging. If you’ve released a piece of software that’s experiencing significant problems that don’t seem to be an easy fix, then the best thing to do is deconstruct it and go through the code line-by-line until you can find out where the issues are.

The easiest way to do this is of course to obtain the original source code, but this is often easier said than done. Maybe the code got lost, perhaps an angry developer deleted it, or you’re a competitor who’s seeking to fix the errors and release your own improved version.

Software reversing is the key to understanding. Here are some other popular reasons why people do it:

  • To research computer viruses and how they operate
  • To learn about advanced algorithms and how they work
  • To research database structures and how their network communication works
  • To check their own resistance to reverse engineering
  • To improve errors and improve compatibility with other programs and operating systems

How To Reverse Engineer Software

Reverse engineering software is like taking apart a car and trying to put it back together. You Need to know how it works in the first place, and you need the proper tools to take it apart and put it back together. For instance, if you want to increase your vehicle’s horsepower, then you are going to need to know how engines work.

After you understand the basic principles, then you can use your tools to take the engine out, take it apart, and make unique modifications so that the horsepower increases. Reverse software engineering is no different.

Theoretical Knowledge and Principles

This is the most important part. If you don’t understand the basic functionality behind a piece of software, then you have no hope of reverse engineering it. You should be able to look at a program and immediately be able to replicate certain parts of it or understand the basics of how it works.

If you are reverse engineering for a specific purpose such as reconstructing algorithms, finding a virus, or for cryptography, then you need to be well-versed in these principles.


The compiled executable file and the source code are two completely different things. To be able to understand the code and break it down to its original structure, then you’re going to need some tools.


This is the most important software in your toolkit. Disassemblers will take an executable file and break it down into the original source code. Many disassemblers break the code down into what’s called UML (Unified Modeling Language). From here you will have to reconstruct the principles into the specific language that you want. It’s important to understand that they can’t always do this perfectly. However, they get about 90% of the code right. You will have to use your theoretical knowledge to fill in the blanks.


If you are using the software reverse engineering process to find bugs in your program, then a debugger can go a long way to help. In OllyDbg, for example, you can set the debugging software to find specific errors in the source code to prevent you from having to read everything line-by-line.


When you’re trying to reconstruct large blocks of code, having a visual aid is incredibly helpful. In Erwin, for example, you can create visual layouts of your code and the operating process to help you better understand which code is responsible for which actions. You can do the same thing in Visio (a Microsoft product) or in ODI (Oracle Data Integrator).

The Difference Between Binary and Source Code

You need to understand that you will rarely ever have access to a software’s exact source code. When developers deploy the software, they first put the code through a compiler. The compiler takes the code (written in any language) and translates it into what’s called binary code (0’s and 1’s) that a computer can understand. When reverse engineering, you are taking this binary code and doing your best to translate it back into readable, understandable code.

Commonly Asked Questions

Can You Reverse Engineer C++ Code?

While it is possible, it is very hard to do. Most C++ programs are high-profile, and developers specifically write obfuscated code to make it hard for reverse engineering. They do this to prevent people from stealing their code and making cheap knock-offs. That being said. However, it can be done. It’s theoretically impossible to write fully obfuscated code. Developers can write their program to intuitively resist disassemblers, though. In the C++ reverse engineering process, you will have to use a lot of human intuition and knowledge about the system’s architecture to fill in the blanks.

How to Reverse Engineer Drivers

Reverse engineering USB drivers is a subject of fun for many coders. It’s not usually used for anything particularly useful, but you can do some pretty cool projects. Most USB devices that you use will utilize Windows. If you want to customize them and recode them for your own personal fun (such as programming an led keyboard or mouse to have special color patterns), you will need to change the USB to a Linux driver.

Once you’ve done that, then you can write additional Linux programs that will be able to interact with and control your USB device in whichever way you see fit.

Final Thoughts

Whether you’re trying to take apart software for educational purposes, or you’re trying to replicate your own version of it, reverse software engineering can be a rewarding process. While modern tools make it a lot easier, you will still need to make use of your existing computer science knowledge.

In most software reverse engineering examples, there is no way that you can perfectly replicate the original code that was produced. You can, however, get very close. If you are willing to put in the effort, however, you will find it to be a rewarding process.

About the author

Steven Hansen

Steven Hansen is a founder of Techeries. He is a specialist in digital security solution business design and development, virtualization and cloud computing R&D projects, establishment and management of software research direction. He also loves writing about data management and cyber security.