ollydbg cracking tutorial


The context menu in the previous figure shows that both 00401055 and 00401063 contains JA (jump above) to the PUSH 10 used for message box. This will bring up the Calls window. We now want to type in the offset value that we wrote down, in this case 0001A915. Next go back to the PUSH 10 instruction of the MessageBoxA by pressing the minus sign key (-) and repeat the process for the JE from 0x401064. Click OK and we get to the main screen: Notice it says “unregistered” at the top in the title bar. Before pressing the Run key we want to set some breakpoints first. In the top dialog box type eight 0’s (00000000) and in the second type eight F’s (FFFFFFFF). Soon you will get to the main screen: and you will see that we are still registered. This program has a time restriction, and after this time, it will not work anymore. Right-click in the Code window of Olly and choose Search For, select All Intermodular Calls. So this is basically another registration check, and if it fails if puts a zero in the registered/not-registered flag. OllyDbg has many context menus. The Handles window shows the object type, reference count, access flags, and the object name for each handle owned by the process. Notice it’s now at a different memory address: Then right-click on the first value in the dump that we edited and choose”Breakpoint” -> Hardware, on write” -> “byte”: When reverse engineering an app, I generally stay with hardware breakpoints as they are harder for the app to detect.

We can tell for sure by running an ID program, but we’ll get into that in a future tutorial. Press Run again to see if there is another set of characters to be added. Re-start the app and Olly will break. Now run the app. OllyDbg has a Call Stack window that is very useful in observing the call stack for the current thread. OllyDbg , PEiD , W32dasm, HexWorkshop. Lets first try the easy way. Instead, we will use the power of the debugger to help us locate the error message. We are going to patch the jump that returns the invalid registration box. Now let’s remove our hardware breakpoint “Debug” -> “Hardware breakpoints” and delete it, and let’s place another hardware breakpoint at address 9ADBF4 so that we can break before this routine has run: Now you may wonder why I didn’t just put a regular breakpoint on this. Notice in the API information section in Figure 19 shows the MessageBoxA call and its parameter’s just above it. The problem with this is that changing the DL to a one will add a byte to the length of this instruction, and this will overwrite our RETN statement.What about if we replace the compare and jump instructions and instead just load 01 into DL. 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: Figure 20: The Hints pane shows two places that jump to this error message box. Write this number down.. ignore the “h” at the end it just means that the value is hexadecimal. We don’t know, in which programming language or under which platform this software is developed. Go ahead and keep running and we will break in our modified registration check routine, and it will put a 01 into our address again as we planned. Validate the serial and then close WorldTV. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. There are usually two places a serial is stored! This will bring up the assemble window. That is why as we stated earlier, assembly programming knowledge is necessary when reversing with native executable. The OllyDump plug-in will come in handy during manual unpacking and it contains two heuristics for locating the OEP (Original Entry Point).

Clicking on that conditional jump at address 9AABA5: we can see that if the result is equal, we will jump to the “unregistered” version of the string. We are going to start by opening Ollydbg. We want to chose ‘write’ because somewhere a zero is being written to this address. Open up worldtv. To do this we will need to find where the jne instruction is located in WorldTv.exe. You will find soon after that point that you come to here: Notice that EAX, EBX, and EDX were all zeroed out. Open up WorldTV2.exe in HexWorkshop.

Run it again and Olly will break in a new section: If you look in the bottom left corner of the OllyDBG window, you will see that we broke on our hardware breakpoint: Now, let’s study this code. Keep hitting ctrl-L until we come to the following: Now that looks a lot better. For example, the key sequence of Alt+B will open the Breakpoints window to view all of the breakpoints set in your debugging session. Try putting in a random key.

OllyDbg is a 32-bit disassembler/debugger for Microsoft Windows binary files. In this tutorial we are going to take off the training wheels and crack a real program. OllyDbg has many context menus. EAX+15B8 is just a memory address, in this case a global variable as it starts with DS:. Type in “regedit”, without the quotes, and press enter. The MSDN API documentation site (www.MSDN.microsoft.com) is a useful resource in looking up these functions to learn what they do, the parameter’s these functions take in, and what these functions return. Paying attention to EDI earlier we know that our serial is either 4 sets of 8 characters or 3 sets of eight characters. To be totally honest, after cracking the program in this tutorial, I liked it so much I paid for the registration and now use the app legitimately. What we need to do is find where this is being set and make sure it doesn’t happen. It asks for a serial! Right-click, choose “Search for” -> “All referenced text strings” and the search window will open. When you only have 2 characters left to go stop pressing the Run button and just step through the code. Olly will disassemble the binary file and it will look something like Figure 15.

Double clicking on our new, patched binary should result in: Today we learned our way around OllyDbg and used that information to debug, reverse, and defeat an expiration lock of a “trial” piece of software. There are several hotkeys that you will find useful during your debugging session. This key single-step traces one instruction at a time. Let’s place a BP on this JE instruction and start the app: Olly will break at this line and you will notice that we are going to jump to the bad boy. Now, I noticed that the word “registration” and “registered” were used a lot earlier, so let’s search for them. When you step past the following line REP MOVS BYTE PTR ES:[EDI],BYTE PTR DS:[ESI] you will see the last two characters of your serial added on. Re-start the app and run it until we break. Change ), You are commenting using your Twitter account. Open the Hardware breakpoints window (“Debug” -> “Hardware breakpoints”) and click the Follow button on our BP.

Just goes to show you you can’t judge an app by it’s downloads. CFF explorer has some built-in functionalities to calculate the MD5 and SHA-1 hashes of our sample. OllyDbg’s View menu will open new windows to view a process’ threads, handles it has open, its layout in memory and breakpoints.

OllyDbg has many context menus. I selected. It has become habit to first examine a target with PEiD to determine the packer or protector. You can right-click on almost anything in OllyDbg to get a context menu to examine your many debugging options. Binary edit the first memory location to 01. Directly before the call to MessageBoxA (in red color right-pane), four parameters are pushed onto the stack. That way, on the last line, DL will be moved into our memory location! We know that 75 is the opcode for the instruction JNE and 74 is the opcode for instruction JE. Posted by Eric Hokanson in Malware RE, Reverse Engineering, OllyDbg Tutorial, Reverse Engineering, Reverse Engineering Malware. Here the PUSH 10 instruction contains the > sign which is referenced by another line of code. Modify the binary to force all code paths to succeed and to never hit the trail expiration code path again. Sort the calls by Destination. By hitting F9 to run the debugger, we should encounter the error message as seen in Figure 16. Surprisingly, the target is not packed or protected. Load the expired program in order to understand what is happening behind the scene. We now know that WorldTV checks the registry for a serial before loading. give it any one you want, We will use 1234567. OllyDbg is a general purpose Win32 user-land debugger. With our tour of Olly behind us, we are now ready to start doing some real work: reversing and cracking a “trial” piece of software. Aha! This will go back and forth a couple times until finally: We are now registered!!!! A box will open asking you to “Type the name of a program, folder, etc…”. Select the line and press F2 to set a breakpoint.

First, it is usually a good idea to configure OllyDbg to ignore exceptions and to show loops. Reversing with Olly. F2 – Set Breakpoint sets a software breakpoint on the currently selected instruction. That will make it all the easier to crack. Nop. This window displays all debugging events such as module loads, thread creations, breakpoint hits, and errors. To do this click on the String References button at the top of w32dasm. Clicking on the about screen shows: Congratulations. You can right-click on almost anything in OllyDbg to get a context menu to examine your many debugging options. If they are not the same, we store the contents of DL into our memory location. If it does, we need to set a hardware breakpoint on it instead. Dependency Walker lists the DLL’s this sample relies on, and we can see that the sample was compiled with Visual Studio C++ 8, which is Visual Studio 2013. After the file has been disassembled, we will look for the string from the messagebox. We can see that a serial is being made and can be seen at this address: MOV EDI,WorldTV.004C8950. Change ), You are commenting using your Facebook account. To view the call stack, press Alt+K. There are also specialized tools for dealing with Delphi programs, but fortunately we do not need to use them in this tutorial (we will get to them though ). You should have a good understanding of Intel x86 assembly opcodes; not how to program but at the very least, know how to it. Figure 10: Configure Olly to Ignore Exceptions. Scroll to the top and right click. The next thing I usually look for is if there is a way to enter a registration code. Lets name it worldtv2.exe we will refer to it later. We need to find out where that serial is being stored. Start up WorldTV2.exe and put in 1234567 as the serial.

Scroll down until you find “Invalid Registration Code” and double click it. It is still asking for a serial.

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