Re: Fixing a bug in executable file

On Jul 31, 5:38 pm, kuasha <kua...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
It is totally application specific where the authentication procedure is.
Possibly it is near the application entry point. You can use debugger like
softice to track the application execution and find the code. When you find
that just place NOPs or a JMP to the code after the authentication. It is
hard to tell how to do that without seeing the executable.

--
Sincerely,
Maruf Maniruzzaman,
Software Engineer,
KAZ Software Limited,
Dhaka, Bangladesh.http://www.kaz.com.bdhttp://www.kuashaonline.com



"anshul makkar" wrote:
On Jul 26, 11:38 am, Donald <Don...@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
I think its a great idea. Disassemble the executable and replace that
authentication related code with NOP. You can use a hex editor to do that.

"kuasha" wrote:
You can use virtual parallel port style solution. But why bother? Dos
applications are simple enough to change them. The authentication process
possibly near the entry point. Insertion of some NOP could solve that.

--
--
Sincerely,
Maruf Maniruzzaman,
Software Engineer,
KAZ Software Limited,
Dhaka, Bangladesh.
http://www.kaz.com.bd
http://www.kuashaonline.com

"anshul makkar" wrote:

Hi,

My client has a very old DOS software that runs his digitizer.

The software consists of an exe file and a set of other helper files.

When we start the software we have to attach the hardware device to
the system's parallel port which acts as an authentication mechanism.

The problem is that our client has lost the hardware device as a
result the software has been locked.

THus, our client want's us to break the lock so that the software
becomes usable without any hardware device.

We don't have the source code or any other helper source file. We just
have an executable file and a set of other helper files.

Please suggest any approach through which the above task can be
achieved.

Can we manipulate/hook the control flow in the executable so that the
code that checks for the lock can be bypassed ?

How can I use disassembling to my advantage.

This is my first project of this kind. Earlier I have used
disassembling to write video drivers and to understand the softwares
logic but never to break lock or to use the disassembled code to fix
the bugs. I am totally cluless regarding how to start and from where
to start. .

Please if you have any suggestions or help material then do share .

Thanking You
Anshul Makkar- Hide quoted text -

- Show quoted text -

Hi,

Thanks for the suggestions and for discussing various approaches.

As you are aware that the code will be in disassembled form so please
can you give a little more details of how to go about identifying the
authentication code and to replace it with NOP. Please share
suggestion , any link or reference material.

After modification of the disassembled code , do I need to again
recompile the assembled code.

Thanks.- Hide quoted text -

- Show quoted text -

Thanks for the reply. I will do the desired modification.

Thanks a lot for the suggestion.

.

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