A Beginner’s Guide to Software Cracking

Hello, everybody, my name is Rowan, and today we’re going to do a basic introduction to reverse engineering and cracking. First of all, a disclaimer: cracking commercial software is illegal. What I am doing here is entirely legal as this is a “crackme,” a digital puzzle designed to be played in the same way that you crack software.

Exploring Tools for Reverse Engineering

One crucial aspect of reverse engineering is the use of appropriate tools. I thought I would show a cool site called Dogbolt, which is a decompiler explorer. We can upload a binary to this site and see how different reverse engineering tools, including Binary Ninja, Ghidra, and Hex-Rays (the one for IDA Pro), handle the decompilation. It’s worth noting that Hex-Rays is more expensive, but it offers better variable naming and generally better decompilation results. However, I always recommend having Ghidra installed, as it’s free, and sometimes using a different tool can provide better results.

In our example, we can see how Binary Ninja handles the decompilation beautifully, recovering all the types, while Ghidra does not perform as well in certain functions. Hex-Rays also shows its strengths by providing better variable naming, which can be critical when trying to understand complex binaries. Comparing these tools is important because different software might yield better results depending on the tool used. Always having multiple tools at your disposal can help you get a clearer picture of the binary you’re analyzing.

Cracking a Simple Program

Now, let’s dive into the process. We start with a simple crackme that requires a username. When we input a username, the program fails, so we need to understand how to bypass this check. The first step in reverse engineering is to analyze the binary. You can use a debugger or some reverse engineering static software. I prefer Binary Ninja, though I also have Ghidra.

In our example, we can see a function that checks the username length. Our username must have at least four characters; otherwise, the program fails. By analyzing the code, we can figure out the conditions for success. A common technique involves binary patching, where we modify the jump instruction in the binary to change the program’s behavior.

We simply hit “assemble” and replace the “jump if not equal” with a “jump if equal.” After saving the modified binary, we can test it to see if our patch worked. This kind of patching can be done using various tools, each offering different methods to achieve the same goal. The key here is to understand what the binary is doing and modify it to achieve the desired outcome.

Debugging and Extracting the Serial Key

Sometimes, binary patching isn’t enough, and we need to delve deeper. By setting breakpoints in the debugger and observing the memory addresses, we can extract the serial key used by the program. This involves looking at specific addresses in memory and comparing them with the user input to see if they match the expected serial key. Once we have this information, we can craft a key that will pass the program’s checks.

For example, when we run the debugger, we hit a breakpoint and then observe the memory address that holds our password. By following that memory address, we can see what the program expects. We can then copy the serial key before resuming execution and use it to pass the check.

This method is powerful because it allows us to understand how the program is validating our input and how we can manipulate it to our advantage. It’s not just about bypassing the check, but understanding the logic behind it.

Writing a Key Generator

One interesting aspect of reverse engineering is writing a key generator (keygen). This process involves understanding the algorithm used by the software to generate valid keys. In some cases, the key generation algorithm takes a username or an email address and generates a single possible valid key. However, not every keygen algorithm works this way; some are more complex.

In our example, after analyzing the binary, we found a simple check that verifies if a number is divisible by seven. By reverse engineering this process, we can write a keygen that generates valid keys for the software. We first converted the hex values to characters and then figured out that the program uses a checksum to validate the key. By replicating this logic, we can generate a valid key that the program will accept.

It’s important to note that this approach only works if the key generation algorithm is simple enough to be reverse-engineered. Some algorithms are far more complex and require deeper analysis.

Modern Software and Keygens

It’s important to note that while writing keygens can be an interesting challenge, modern software typically uses online activation methods, making traditional keygens less effective. Most modern keygens are either for show or patch the key validation process to bypass online checks.

Depending on how the software is written, there are roughly two ways of dealing with key validation. Some software completely patches the key validation, making the keygen more of a formality. Others may still use an offline activation method, which can sometimes be reverse-engineered.

The reality is that no major commercial software today relies on simple key algorithms for protection. Instead, they use more sophisticated methods, including online checks and server-side validation, making traditional keygens obsolete in most cases.

Conclusion

In this introduction to reverse engineering and cracking, we explored the basics of analyzing binaries, patching software, and writing keygens. Remember, this content is for educational purposes only. Cracking commercial software is illegal, and this tutorial is focused on understanding the underlying principles of software protection and reverse engineering. If you enjoyed this article, please let me know in the comments below, and I’ll be happy to create more content on reverse engineering. Bye for now!