Reverse engineering is the process of taking a compiled binary and attempting to recreate (or simply understand) the original way the program works. A programmer initially writes a program, usually in a high-level language such as C++ or Visual Basic (or God forbid, Delphi). Because the computer does not inherently speak these languages, the code that the programmer wrote is assembled into a more machine specific format, one to which a computer does speak. This code is called, originally enough, machine language. This code is not very human friendly, and often times requires a great deal of brain power to figure out exactly what the programmer had in mind.
What is reverse engineering used for?
Reverse engineering can be applied to many areas of computer science, but here are a couple of generic categories:-
- Making it possible to interface to legacy code (where you do not have the original code source).
- Breaking copy protection (ie. Impress your friends and save some $$).
- Studying virus and malware.
- Evaluating software quality and robustness.
- Adding functionality to existing software.
The first category is reverse engineering code to interface with existing binaries when the source code is not available. I will not be discussing this much, as it is boring.
The second category (and the biggest) is breaking copy protection. This means disabling time trials, defeating registration, and basically everything else to get commercial software for free. This we will be discussing at great length.
The third category is studying virus and malware code. Reverse engineering is required because not a lot of virus coders out there don’t send instructions on how they wrote the code, what it is supposed to accomplish, and how it will accomplish this (unless they are really dumb). This is a pretty exciting field, but requires a great deal of knowledge. We will not discuss this much until later on.
The fourth category is evaluating software security and vulnerabilities. When creating large (think Windows Operating Systems), reverse engineering is used to make sure that the system does not contain any major vulnerabilities, security flaws, and frankly, to make it as hard as possible to allow crackers to crack the software.
The final category is adding functionality to existing software. Personally, I think this is one of the most fun. Don’t like the graphics used in your web design software? Change them. Want to add a menu item to encrypt your documents in your favorite word processor? Add it.
What knowledge is required?
As you can probably guess, a great deal of knowledge is necessary to be an effective reverse engineer. Fortunately, a great deal of knowledge is not necessary to ‘begin’ reverse engineering, and that’s where I hope to come in. That being said, to have fun with reversing and to get something out of these tutorials you should at least have a basic understanding of how program flow works (for example, you should know what a basic if…then statement does, what an array is, and have at least seen a hello world program). Secondly, becoming familiar with Assembly Language is highly suggested; You can get thru the tutorials without it, but at some point you will want to become a guru at ASM to really know what you are doing. In addition, a lot of your time will be devoted to learning how to use tools. These tools are invaluable to a reverse engineer, but also require learning each tool’s shortcuts, flaws and idiosyncrasies. Finally, reverse engineering requires a significant amount of experimentation; playing with different packers/protectors/encryption schemes, learning about programs originally written in different programming languages (even Delphi), deciphering anti-reverse engineering tricks…the list goes on and on.
There are many software which are used for this purpose. I will be using Olly Debugger.
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