Self keygenning with OllyDbg

All the information shared in this website is seriously, only for educational purposes.

In our previous post, we learnt about codecaving ( Read this previous post if you havn't. It is important to understand this post.) . In this tutorial, we will learn about how to self keygen a simple crackme program. Self keygenning means, to make a program print its real serial number or any other string by itself.
You can download the program from here : Download

Open up the crackme in OllyDbg, and search for all referenced strings( This is not a very good idea to check the referenced strings while dealing with real life applications, but its ok to use here) . You will see a string "Key:" . Double click on it.

Now, put a Breakpoint ( These break points are used to run till the selected instruction. All the code above it will be executed and the debugger(ollydbg) will stop executing at the point where we kept a breakpoint). Put a break point on the instruction "CALL 00403000" by pressing F2 .  

Now click the play button on the top to run it. The program will run and stop at that point. You need to enter your name in program.

Now, you will have to Step over( by pressing F4) each instruction. Do that continuously , until the program asks you to enter the key too. Once it asks to enter the key, type anything simple like 1234.

Now, again Step over until you see your key in the program i.e., the next instruction to be executed should be "MOV EAX, 402521" . Just like in the pic :

Below our key "1234" , we see another string "3d7z6H262679d" . It is our key which was calculated by the algorithm in that program from our name( In next tutorial, I will show how to find these algorithms). We can see, that it is moved into edx at "MOV EDX, 402922" . So, all we need to do is, turn the program to print the value of EDX after it calculates the real key from the name we entered. To do that,  just NOP the code below our key at "MOV EDX. 402922" till "PUSH EAX" as shown in the image : 

Now, edit PUSH EAX and change it into PUSH EDX . Save this file and run it. It will print our key by applying an algorithm on our entered name.

                            

And thats how Self keygenning is done :) Thank you. In next post I will show how to make a keygen by ourself by learning the algorithm of that program.