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but you won t be cracking real copy protections. That would not only be illegal, but also immoral. Instead, I will be demonstrating cracking techniques on special programs called crackmes. A crackme is a program whose sole purpose is to provide an intellectual challenge to crackers, and to teach cracking basics to newbies . There are many hundreds of crackmes available online on several different reversing Web sites.
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Let s take the first steps in practical cracking. I ll start with a very simple crackme called KeygenMe-3 by Bengaly. When you first run KeygenMe-3 you get a nice (albeit somewhat intimidating) screen asking for two values, with absolutely no information on what these two values are. Figure 11.1 shows the KeygenMe-3 dialog. Typing random values into the two text boxes and clicking the OK button produces the message box in Figure 11.2. It takes a trained eye to notice that the message box is probably a stock Windows message box, probably generated by one of the standard Windows message box APIs. This is important because if this is indeed a conventional Windows message box, you could use a debugger to set a breakpoint on the message box APIs. From there, you could try to reach the code in the program that s telling you that you have a bad serial number. This is a fundamental cracking technique find the part in the program that s telling you you re unauthorized to run it. Once you re there it becomes much easier to find the actual logic that determines whether you re authorized or not.
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Figure 11.1 KeygenMe-3 s main screen.
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Figure 11.2 KeygenMe-3 s invalid serial number message.
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Unfortunately for crackers, sophisticated protection schemes typically avoid such easy-to-find messages. For instance, it is possible for a developer to create a visually identical message box that doesn t use the built-in Windows message box facilities and that would therefore be far more difficult to track. In such case, you could let the program run until the message box was displayed and then attach a debugger to the process and examine the call stack for clues on where the program made the decision to display this particular message box.
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Let s now find out how KeygenMe-3 displays its message box. As usual, you ll try to use OllyDbg as your reversing tool. Considering that this is supposed to be a relatively simple program to crack, Olly should be more than enough. As soon as you open the program in OllyDbg, you go to the Executable Modules view to see which modules (DLLs) are statically linked to it. Figure 11.3 shows the Executable Modules view for KeygenMe-3.
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Figure 11.3 OllyDbg s Executable Modules window showing the modules loaded in the key4.exe program.
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This view immediately tells you the Key4.exe is a lone gunner, apparently with no extra DLLs other than the system DLLs. You know this because other than the Key4.exe module, the rest of the modules are all operating system components. This is easy to tell because they are all in the C:\WINDOWS\ SYSTEM32 directory, and also because at some point you just learn to recognize the names of the popular operating system components. Of course, if you re not sure it s always possible to just look up a binary executable s properties in Windows and obtain some details on it such as who created it and the like. For example, if you re not sure what lpk.dll is, just go to C:\WINDOWS\SYSTEM32 and look up its properties. In the Version tab you can see its version resource information, which gives you some basic details on the executable (assuming such details were put in place by the module s author). Figure 11.4 shows the Version tab for lpk. from Windows XP Service Pack 2, and it is quite clearly an operating system component. You can proceed to examine which APIs are directly called by Key4.exe by clicking View Names on Key4.exe in the Executable Modules window. This brings you to the list of functions imported and exported from Key4.exe. This screen is shown in Figure 11.5.
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