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I am new to reverse engineering so this seems like a very basic issue, and still I was not able to find an answer to it myself yet. Hopefully someone can point me in the right direction.

I am on Windows, I disassembled an exe file using "PE Explorer". For now, my process was to somehow, mostly by trial and error, identify the machine code steps I want to change in the dissasembly, then make the necessary change by opening the same exe in a hex editor, finding the same instruction and changing it there.

(Side note here: This two step process is quite inefficient. Is there a program you can recommend where I can combine both steps in one go, or at least side by side?)

While this has worked for me so far, I believe there must be a better way than doing this by trial and error and manually trying to identify the functions in the machine code. Is there? Particularly, is there a way to run a program (exe) and in parallel follow the steps in the dissasembly (ideally slowed down..)?

Thank you.

  • Use a debugger like OllyDbg which can patch executables. – 0xec Oct 16 '15 at 13:18
  • cdb -c "bp $exentry;g" <yourexe> or windbg -Q -c "bp $exentry;g" <your exe" will break on WinMainCrt . etc etc (the Address of Entry point in PeHeader) – blabb Oct 16 '15 at 13:53
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Particularly, is there a way to run a program (exe) and in parallel follow the steps in the dissasembly (ideally slowed down..)?

Yes, the type of tool you're describing is called a "debugger".

Some popular debuggers for Windows are:

There are plenty of others, but these are some of the most user-friendly.

  • Thanks Jason. Will one of those allow me to make direct changes in the machine code and save back to the same exe? Also, which is your personal favorite? – vic Oct 16 '15 at 14:44
  • OllyDbg v2.01 allows it. You can use an extra plugin for IDA Pro to allow it. Not sure about x64dbg since I so rarely use it. As for my personal favorite, it depends on the requirements. For user-mode x86 debugging on Windows, I use OllyDbg. For user-mode x64 debugging on Windows, I use x64dbg. For kernel-mode debugging on Windows and for user-mode and kernel-mode debugging on non-Windows platforms, I use IDA Pro's debugger. – Jason Geffner Oct 16 '15 at 15:14

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