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Erikina



Joined: 06 Apr 2006
Posts: 8
Erikina
I have an .exe that I would like to make some minor changes to. The author said he will not give me the c++ source, but if said if I can he doesn't mind if I make changes to it. My question is, what's the best/easiest way for me to edit an .exe which I do not have source to? Is there any way for me to convert the program to the fasm/masm .asm and work with that?

Thank you.
-Eric Springer
Post 22 Jun 2006, 01:39
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Quantum



Joined: 24 Jun 2005
Posts: 122
Quantum
Quote:

Is there any way for me to convert the program to the fasm/masm .asm and work with that?

In theory, that's possible, if it's not packed or otherwise protected against RE. Just use a disassembler (IDA Pro is the best one!) to get an equivalent assembler source.

BTW, what kind of modifications do you want to perform?
Post 22 Jun 2006, 02:11
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comrade



Joined: 16 Jun 2003
Posts: 1137
Location: Russian Federation
comrade
that's the funniest post i've seen in months
Post 22 Jun 2006, 03:30
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Erikina



Joined: 06 Apr 2006
Posts: 8
Erikina
Quantum wrote:
BTW, what kind of modifications do you want to perform?
I'm just modifying an American Option calculator program to handle Australian options (modifying shares per contract from 100 to 1000). If I am able to do that, I want to try add stuff like Australian frank dividend calculations - but that's probably a bit too much for me.

So if I use IDA Pro and get the assembly listing - will I be able to assembly that in MASM 8? I guess if I can get to that stage I should have a decent chance of getting my way through it.

Thanks!
-Eric Springer
Post 22 Jun 2006, 04:44
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
you will only need to change one constant (2 or 4 bytes) in executable. finding this constant will be the problem.
Post 22 Jun 2006, 09:01
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Quantum



Joined: 24 Jun 2005
Posts: 122
Quantum
Quote:

So if I use IDA Pro and get the assembly listing - will I be able to assembly that in MASM 8?

After some minor changes and assuming IDA produced a 100% correct listing, which isn't true most of the time. You don't need to disassemble the whole program to change just a couple of bytes. Better use a debugger to find thouse bytes and patch 'em directly.
Post 22 Jun 2006, 13:56
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HyperVista



Joined: 18 Apr 2005
Posts: 691
Location: Virginia, USA
HyperVista
Ollydgb may help you find your patch points without availability of source code. www.ollydbg.de
Post 22 Jun 2006, 15:31
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Erikina



Joined: 06 Apr 2006
Posts: 8
Erikina
Thanks everyone for your reply.
HyperVista wrote:
Ollydgb may help you find your patch points without availability of source code. www.ollydbg.de
If I find the value I would like to change, does ollydbg allow me to make the change and test the modified exe?

-Eric Springer
Post 22 Jun 2006, 22:22
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peter



Joined: 09 May 2006
Posts: 63
peter
Yes, this is exactly what OllyDbg does.
Post 23 Jun 2006, 01:53
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HyperVista



Joined: 18 Apr 2005
Posts: 691
Location: Virginia, USA
HyperVista
Attached is the Ollydbg "Quick Start Guide" (MS Word format). It's kinda fun stepping through the FASM "Beer" demo in ollydbg. Very Happy


Description:
Download
Filename: Ollydbg Quick Start Guide.doc
Filesize: 61 KB
Downloaded: 242 Time(s)

Post 23 Jun 2006, 11:43
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