With that, you can use a disassembler like IDA Pro to analyze the code more closely and try to understand what is going on, and how you can bypass it. It really just comes down to a good understanding of software and a basic understanding of assembly. Hak5 did a two-part series on the first two episodes this season on kind of the basics of reverse engineering and cracking. It's really basic, but it's probably exactly what you're looking for.
A would-be cracker disassembles the program and looks for the "copy protection" bits, specifically for the algorithm that determines if a serial number is valid. From that code, you can often see what pattern of bits is required to unlock the functionality, and then write a generator to create numbers with those patterns. Another alternative is to look for functions that return "true" if the serial number is valid and "false" if it's not, then develop a binary patch so that the function always returns "true".
Everything else is largely a variant on those two ideas. Copy protection is always breakable by definition - at some point you have to end up with executable code or the processor couldn't run it. The serial number you can just extract the algorithm and start throwing "Guesses" at it and look for a positive response.
Computers are powerful, usually only takes a little while before it starts spitting out hits. As for hacking, I used to be able to step through programs at a high level and look for a point where it stopped working. Then you go back to the last "Call" that succeeded and step into it, then repeat. Back then, the copy protection was usually writing to the disk and seeing if a subsequent read succeeded If so, the copy protection failed because they used to burn part of the floppy with a laser so it couldn't be written to.
Then it was just a matter of finding the right call and hardcoding the correct return value from that call. I'm sure it's still similar, but they go through a lot of effort to hide the location of the call. Last one I tried I gave up because it kept loading code over the code I was single-stepping through, and I'm sure it's gotten lots more complicated since then.
I wonder why they don't just distribute personalized binaries, where the name of the owner is stored somewhere encrypted and obfuscated in the binary or better distributed over the whole binary.. AFAIK Apple is doing this with the Music files from the iTunes store, however there it's far too easy, to remove the name from the files.
I assume each crack is different, but I would guess in most cases somebody spends a lot of time in the debugger tracing the application in question. The serial generator takes that one step further by analyzing the algorithm that checks the serial number for validity and reverse engineers it.
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Apart from being illegal, it's a very complex task. It is decrypted when loaded into memory but then they refuse to start if they detect that an in-memory debugger has started, In essence it's something that requires a very deep knowledge, ingenuity and a lot of time!
Anyway, a very good reason to know all this is if you want to write your own protection scheme. Improve this answer. The final result should be 10h. So, the same thing as the second part of the serial is happening here, the only difference is that the resulted value should be 12h instead of 10h. Then we have the conditional jump that will take us to the unwanted message when the resulted value differs from 12h. So now, we need to program a Keygen that will generate an infinite number of Random serials.
So you will have to write it in your favorite programming language. So to practice you are freely welcome to write the Keygen in any language you want and why not e-mail me your keygen to check it. One of the problems that you may face is how to code a keygen that will make you able to generate random characters for the serial. In addition, setting conditions in the code is obligatory to get the value in a specific range Printable Characters. Windows is providing CryptGenRandom function for this purpose.
The second one is decided by the serial checking algorithm that will show you if there are additional conditions for example the Software will not accept a serial where two identical consecutive characters are provided. This is the main reason why the serial generation process may take some seconds, because the keygen will keep looping until the right value is found relaying on conditions provided.
We can consider this as a drawback. However, we can turn this into a positive point in our keygen with a message that is telling the user to wait for a couple seconds until the valid serial is generated. In the KeygenMe that we analyzed you noticed that each part of the serial 4 characters in each part is checked alone, and also it depends on simple math operations like addition and substraction.
So to generate a valid part of the serial we will need to set 3 random characters and solve a simple equation to determine the missing characters to get a valid serial. Now, you may realize that additional loops must take place which will check if the result of the equation is also a printable ASCII character or not. You will be able to generate multiple valid serial numbers for the KeygenMe by pressing Return key. In this article you were able to see how to analyze a Serial Checking Algorithm and code a valid key generator that will help you generate different serial numbers.
No hashing or cryptography was present in this KeygenMe and the algorithm was quite simple. In the next part I will try to introduce a more harder KeygenMe with a complete tutorial on how to code a valid Keygen for it. A new tab for your requested boot camp pricing will open in 5 seconds. If it doesn't open, click here. Souhail Hammou is a Moroccan reverse engineering enthusiast who likes to spend most of his time exploring Windows Internals and playing in CTF contests.
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