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  1. #1
    Veteran Dwar is on a distinguished road Dwar's Avatar
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    Simple CrackMe crack, How To Use OllyDBG

    How To Use OllyDBG and simple CrackMe crack
    Many people wonder what ollydbg is and what it does, well here is a small tutorial on ONE way on how to use it, but there are many more. :P

    Programs needed:
    • Ollydbg
    • Crackme
    • W32Dasm
    I would like to introduce you now to a more advanced and professional cracking technique, cracking using a debugger. What is a debugger? In few words, a debugger is a software that will let us look in the asm code before and after the code is executed by the cpu. The debugger will pause the execution of the code and will allow us to trace it step by step as the cpu executes it. All crackers uses a debugger, even W32Dasm has a debugger built in but is not very comfortable. The most advanced debugger for cracking used by all crackers is OllyDBG, this tool will become your friend, your partner, it will be for you the tool number one!

    Let's do some configurations, press alt+o to access options and go to the CPU menu. Make you settings look like in this picture:
    picture1:

    After this go to EXCEPTIONS menu and make your settings look like in this other picture:
    picture2:

    Ok, we are done for now. We will use olly for everything, like patching, finding serial keys, unpacking, studing, etc.

    We will start our first lesson with olly by finding the serial key of a crackme by FHCF team, during tracing the code it will be very easy to understand where we should patch if needed.

    Our mission in this lesson is to find a serial key for our entered name.

    Step 1:

    Run the crackme and you will see that it needs a name and a serial number, enter some fake info... click on check serial... :? nothing happens Lets find a real serial for our name now!
    Disassemble our target with w32dasm then click on the imports button. See the picture below:
    picture3:

    On the dialog box that shows up find this: USER32.GetDlgItemTextA like in the picture below:
    picture4:

    Select it like in picture above and double click on it, you will land at the address: 004011DF (write down this address), just a bit below this we have an other reference to USER32.GetDlgItemTextA at the address 004011F0 (write this address down too). Close W32Dasm, we don't need it anymore.

    Step 2:

    Run OllyDBG and click on file, open, browse to our crackme and open it. Cool, you should see the asm code now. Press F9 button from your keyboard then the crackme should show up. Enter your name and any serial number but don't click on "check serial" button yet. I will enter MiStEr_X as name and 12345 as serial. Return to OllyDBG then click on "Go to Address" button. This button is indicated in the picture below:
    picture5:

    On the blank box enter the first address we did found on w32dasm, 4011DF then click ok!
    You will be here:
     PUSH 019h
    PUSH 0403096h
    PUSH 066h
    PUSH DWORD PTR SS:[EBP+8]
    004011DF CALL GetDlgItemTextA ;read the entered name
    PUSH 01Eh
    PUSH 0403078h
    PUSH 065h
    PUSH DWORD PTR SS:[EBP+8]
    004011F0 CALL GetDlgItemTextA ;read the entered serial
    CMP EAX,4 ; compare entered name with 4
    JB @crackme__00401245 ; jump if below (if our entered name is smaller than 4 digits then jump)


    GetDlgItemTextA is used in asm to retrieve the information entered by users in blank boxes!

    Now, put the selector line on "004011DF Call GetDlgItemTextA" then press the F2 button from your keyboard to set a breakpoint. Go to the second address to and set a breakpoint there too by pressing F2. See the picture below to see my breakpoints. The addresses highlighted with white means that there is set a breakpoint.
    picture6:

    Bring up the crackme from the taskbar and click on "check serial" Olly will break on the first breakpoint, now press F9 (run) and Olly will break on the other breakpoint we did set. The first breakpoint was for the name we have entered and the second is for the serial number. Now trace line by line slowly with F8 button until you are on the address "0040121F"
    picture7:

    Referring to the picture too, you must be on this line:

    0040121F CMP EAX, EBX

    Let's explain what does this mean, CMP means compare, eax register is storing the fake serial we did enter and ebx register is storing the real serial number for the entered name. Check this on the top-right of your screen, in the above picture are number 2 and 3. EAX has the value 12345 that is the fake serial I did enter and EBX is has the value 2EB. Can 2EB be the real serial number for the name MiStEr_X?? Yes it is, we did found a real serial number and we can find a serial for any name we enter by following the procedure of this tutorial. Enjoy!

    As you see, on the address .40121F the protection of the crackme is comparing our fake serial with a real serial for our name.
    Credits to MiStEr_X And BstChaos
    Attached Files
    Last edited by Grooguz; 2011-12-12 at 10:07 AM.
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  2. #2
    Inactive lveyez is on a distinguished road
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    Re: Simple CrackMe crack, How To Use OllyDBG

    hi..
    i can't see the images ...
    can u help me to send the tutorial by a mil.. ?

  3. #3
    Member-in-training MrSmith is on a distinguished road
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    Re: Simple CrackMe crack, How To Use OllyDBG

    This was very easy
    Ever Danced With The Devil By The Pale Moonlight ?

  4. #4
    Banned spunkman is on a distinguished road
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    Re: Simple CrackMe crack, How To Use OllyDBG

    If you find this easy there are harder ones to do. Take 1 by one and before you know it your king of ollydbg.

  5. #5
    Inactive Leelou is on a distinguished road
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    Re: Simple CrackMe crack, How To Use OllyDBG

    Guys, first... I am totally new at this... but have a program that I just have to crack (all the serials online are defected or infected) and the OllyDBG and W32Dasm do not have all the functions like on these pics... EX: I only have USER32.GetDlgItem function and no button like on PIC 5.

    How to set it up, or some download links would be very helpful....

  6. #6
    Member-in-training MrSmith is on a distinguished road
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    Re: Simple CrackMe crack, How To Use OllyDBG

    Leelou i recommend to watch Lena151's tutorials they will help ALOT. A simple search in google for Lena151 reversing tutorials will shed some light in that dark cave of yours
    Ever Danced With The Devil By The Pale Moonlight ?

  7. #7
    Inactive ingeniere is on a distinguished road
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    Hi,
    I would like to know if someone can help me crack a program.
    Regards

  8. #8
    Inactive coolninja is on a distinguished road
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    Idk how to write a GUI with C yet, I know it in Java,
    but C is my current language, so I made a console keygen for this crackme...
    #include <stdio.h>

    char name[50], *walk;
    int sum = 0;

    int main()
    {
    printf ("Please input your name: ");
    gets(name);
    walk = name;
    while (*walk != '\0') {
    sum += *walk++;
    }
    printf("Serial: %x\n", sum);
    printf("\nPress enter to exit.");
    gets(name);
    return 0;
    }
    p.s. Indent not showing in quote or whatever in this forum...=_="

    Quote Originally Posted by MrSmith View Post
    Leelou i recommend to watch Lena151's tutorials they will help ALOT. A simple search in google for Lena151 reversing tutorials will shed some light in that dark cave of yours
    Yea, I totally agree with watching Lena151's tutorial, that's the best tutorial ever!
    Last edited by coolninja; 2011-04-03 at 06:56 PM.

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