Right click the 0x00401055 instruction inside the CPU window and select binary where click over. The Executable Modules Window shows the base virtual address, the virtual size (the size the binary takes up in memory), the Entry Point’s virtual address, the module name, file version, and file path for each module loaded in the process. So if we make sure a 1 is put into that memory location every time this routine is run, then any other routines will check that memory location and see that it is a 1 and think that we’re registered. By doing this testing before the product become publically available, we can modify the code to make circumvent of copy protection more sophisticated before its release. Now, we could just put in a serial every time we use it but that is annoying.

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. Then right-click and choose “Show Call” (see Figure 18). In this case rather than jumping on bad serials we want the program to jump on ANY serial. Since we are still paused on the first line of this routine, you can single step to see DL being loaded with 1, and then the 1 being put into the memory address (you may need to go to the proper address in your dump as Olly has probably reset it again). Figure 11: Debugging Options to Show Loops. Nop. Olly will disassemble the binary file and it will look something like Figure 15. Once your two jumps to the error message are patched with NOPs, save the modifications by right-clicking in the CPU window, click on “Copy to Executable”, and then select “All Modifications.

Go ahead and close Ollydbg. The Windows window displays the Handle, Title, Parent Window, Window ID, Window Style, and Window Class Information for each window owned by the process. At this point, the question we are now faced with is where to begin? OllyDbg is a general purpose Win32 user-land debugger. Select the USER32.MessageBoxA near the bottom of the call stack and right click and choose show call as following; It shows the starting point in which the assembly call to MessageBoxA is selected. A new window opens up with a list of all strings found in the file. It checks for a serial when starting up Then enter MOV DL, 1: Click Assemble then Cancel. The objective of writing this paper is to manifest, how to crack an executable without peeping its source code by exercising OllyDbg tool.

Reversing with Olly. You will also need the following tools: F7 – the Step Into command. To demonstrate the power and functionalities of OllyDbg, we will use a sample that has some copy protections. Choosing the “View names” (Ctrl-N) opens the Names Window. When we attempt to load SoftwareExpiration.exe file, it will refuse to run because the current date is past the date on which the authorized trial expired. The Names Window shows the list of imported and exported functions for a given module. This will bring up the Calls window. You should now be on code at location 0x00401055. Set a breakpoint on the compare line (9AAB9E) and delete our other BP. Right click on the instruction at location 0x401060 inside the CPU window and select “Binary” and then click on the “Fill with NOPs” as shown in Figure 22.

Two recommended plug-ins you should get are OllyDump to dump a process’ memory and Olly Advanced to get around any anti-debugging a malware sample may throw against you. The result: “Microsoft Visual C++ 5.0”. Say we downloaded a trial piece of software that expires after a certain date or after 30 days.

Reversing with Olly. It looks like as following; Now open the SoftwareExpiration.exe program in OllyDbg IDE from File à open menu and it will decompile that binary file.

Highlight everything we changed, right-click and select “Copy to executable”. Now it is time to do some modification in the binary code. Typically in copy protection, the user is obligatory to register first for the product before use.

Clicking on the about screen shows: Congratulations. After registering with a bogus serial it is unregistered the next time you start it up. 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. EAX+15B8 is just a memory address, in this case a global variable as it starts with DS:. The window shows the virtual address of all software breakpoints currently set, the active status (always, disabled), and the disassembly instruction of the breakpoint. The next thing I usually look for is if there is a way to enter a registration code. Figure 1: OllyDbg’s Debugging EnvironmentThe following figure gives the “lay-of-the-land” inside the debugger and its various components. We know that 75 is the opcode for the instruction JNE and 74 is the opcode for instruction JE. The OllyDump plug-in will come in handy during manual unpacking and it contains two heuristics for locating the OEP (Original Entry Point). 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. OpenRCE (www.openrce.org) has OllyDump, Olly Advanced, and many other useful plug-ins to help hide the debugger from malware attacks or to help automate your dynamic analysis process. 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. They are: In OllyDbg’s menu bar, the Debug menu allows you to set both hardware and software breakpoints, single step instructions, restart the debugging session, perform conditional tracing , or to set commandline arguments for the debuggee. We break again on the Recordings registry key so press Run again. Yours will be different than mine, but just notice that the second time through, the memory address that stores the registered/not-registered flag is different.

The objective of writing this paper is to manifest, how to crack an executable without peeping its source code by exercising. In order to explain reverse engineering, we have downloaded the beta version of software from internet which is operative till 30 days. It will open, you now have another list of folders. Change ), Resized to 93% (was 652 x 425) – Click image to enlarge, Resized to 93% (was 651 x 423) – Click image to enlarge, Resized to 98% (was 615 x 33) – Click image to enlarge, Resized to 96% (was 630 x 31) – Click image to enlarge, Resized to 100% (was 606 x 123) – Click image to enlarge, How To Crack A Program Using OllyDBG | Cracking A Program To Obtain Serial Key, Way Of The Cracker | Learn Ethical Hacking, Tutorial : How to Setup and Use A Java DriveBy.

If they are not the same, we store the contents of DL into our memory location. So this is basically another registration check, and if it fails if puts a zero in the registered/not-registered flag. When you are ready press the Go button. In order to prevent the program from hitting this error code path, we can change the jump instruction to a NOP (no operation) instruction.

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