All brand names and product names used in OllyDbg, accompanying files or in this help are trademarks, registered trademarks, or trade names of their. Posts about OllyDbg Tutorial written by Eric Hokanson. Introduction to Cracking with OllyDbg from Scratch (Spanish: INTRODUCCION AL CRACKING CON OLLYDBG DESDE CERO) was written by.
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the analysis with Cheat Engine and furthermore the debugging with OllyDbg. P. Djupfeldt was responsible for the parts where we used TSearch. Coding. Visualizing Binaries With Ollydbg and Graphvis, 16 Sep , Ehab Hussein, MB, 0/5: Not rated. Tracing - An OllyDbg Tutorial, 07 Mar Converted to PDF. Written by Most cracking tutorials say stuff like, this is only for educational purposes and to an OllyDbg/softice - debuger (live debuging).
The Handles window shows the object type, reference count, access flags, and the object name for each handle owned by the process.
Figure 7: OllyDbg has a Call Stack window that is very useful in observing the call stack for the current thread. The Stack window shows the virtual address of stack frame for each function call, the stack contents at that virtual address, the procedure and its arguments as pushed on the stack, as well as who called the procedure.
Reverse Engineering with OllyDbg
The window shows the virtual address of all software breakpoints currently set, the active status always, disabled , and the disassembly instruction of the breakpoint.
You can right-click on this window to disable or delete the breakpoints that have been set. OllyDbg has many context menus.
You can right-click on almost anything in OllyDbg to get a context menu to examine your many debugging options. With our tour of Olly behind us, we are now ready to start doing some real work: First, it is usually a good idea to configure OllyDbg to ignore exceptions and to show loops. In the Exceptions tab, make sure your settings look like Figure Figure Configure Olly to Ignore Exceptions.
To demonstrate the power and functionalities of OllyDbg, we will use a sample that has some copy protections. Say we downloaded a trial piece of software that expires after a certain date or after 30 days. All we get is an error message when we attempt to execute it. The first thing we should do is assess the software with CFF explorer to identify the development language used and some other particulars.
We will need to rely on OllyDbg. Open the CrackMeDemo. In the menu bar, select File then open to navigate to the location of CrackMeDemo. Olly will disassemble the binary file and it will look something like Figure After disassembly, Olly will take us to the entry point, which for this sample is at virtual address 0xE. At this point, the question we are now faced with is where to begin?
Instead, we will use the power of the debugger to help us locate the error message.
By hitting F9 to run the debugger, we should encounter the error message as seen in Figure Now we will attempt to find the time limit checking code. Next press F12 to pause the debugging execution. With the execution paused, we now can search for the code that causes the error message. One way to look for our error message is to examine the current call stack since the error message is currently displayed at this point. From this vantage point you can easily see that the error message string is a parameter of the MessageBoxA function call see Figure Select the USER MessageBoxA near the bottom of the call stack.
MessageBoxA is made Figure The Start of MessageBoxA call in debuggee. The parameters start with the PUSH 10 instruction at 0x Since we are at the PUSH 10 instruction indicated by the grey line , we can examine the Hints pane to see the parts of code that references this call:. The Hints pane shows two places that jump to this error message box. Select the text area of the hints pane and right-click to open a context menu.
It allows you to easily navigate to the code where those jumps are made:. Now we can modify those parts of the code. Select the JNZ from 0x from the context menu. This will take you to the jump command at 0x In order to prevent the program from hitting this error code path, we can change the jump instruction to a NOP no operation instruction.
Resulting Dialog Box after Figure I renamed our fixed CrackMeDemo software and saved it to the desk top. Double clicking on our new, patched binary should result in:.
About me: Executable Software The following sample shows a way of bypassing or removing the copy protection in order to use the product without extending the trial duration or, in fact, without downloading the full version. The copy protection mechanism often involves a process in which the software checks whether it should run and, if it should, which functionality should be allowed.
One type of copy protection common in trial or beta software allows a program to run only until a certain date. In order to explain reverse engineering, we have downloaded the beta version of software from the Internet that is operative for 30 days.
As you can see, the following trial software application is expired and not working further and it shows an error message when we try to execute it. We can easily conclude that this is a native executable and it is not executing under CLR.
This time, we have to choose some different approach to crack the native executable. How can we use this software despite the expiration of the trial period? The following section illustrates the steps in the context of removing the copy protection restriction: The Road Map Load the expired program in order to understand what is happening behind the scenes.
Debug this program with OllyDbg. Trace the code backward to identify the code path. Modify the binary to force all code paths to succeed and to never hit the trial expiration code path again.
Test the modifications. Such tasks can also be accomplished by a powerful tool, IDA Pro, but it is commercial and not available freely. First download OllyDbg from its official website and configure it properly on your machine.
Its interface looks like this: Now open the SoftwareExpiration. Here the red box shows the entry point instructions of the program, referred to as The CPU main thread window displays the software code in form of assembly instructions that are executed in top-to-bottom fashion. That is why, as we stated earlier, assembly programming knowledge is necessary when reverse engineering a native executable.
While the error dialog box is still displayed, start debugging by pressing F9 or from Debug menu. Now you can find the time limit code. Next, press F12 in order to pause the code execution so that we can find the code that causes the error message to be displayed. Directly before the call to MessageBoxA in red color right-pane , four parameters are pushed onto the stack.
Select the PUSH 10 instruction located at C0 address, the line of code that references the selected line is displayed in the text area below the top pane in the CPU windows as follows: Select the text area code in the above figure and right click to open the shortcut menu.Select the PUSH 10 instruction located at C0 address, the line of code that reference the selected line are displayed in the text area below the top pane in the CPU windows as following; Select the text area code in the above figure and right click to open the shortcut menu.
The Start of MessageBoxA call in debuggee.
This will take you to the jump command at 0x So this can be accomplished by changing the JA instruction to NOP no operation which actually do nothing. One type of copy protection common in trial or beta software allows a program to run only until a certain date.
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