Help adding self-checksum data to an EXE/COM 
Author Message
 Help adding self-checksum data to an EXE/COM

Quote:

> Adding a self-authentic verification to an executable:

>   Hi and thanks for reading this :)
>   I'm planning to make a program to do the following:

> - given an .EXE or .COM file as parameter, it would make that file CRC
>   checksum and store it INTO the file.
> - then, if you run the new file and it is modifyed, it would notice you
>   with a message like "Checksum error: file corrupted" and halt. That's
> all.

>   My prob is not the checksum procedure but the one to get control from
>   the .EXE or .COM. I mean:
>                                +--------------+
>   Let's say this is a .EXE     |  executable  |
>                                +~~~~~~~~~~~~~~+
>   I know my prog should make   +-----------------------------------+
>   a new executable like this:  | JMP |  executable  | CRC checksum |
>                                +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
>   where JMP is a jump to the CRC checksum procedure.
>   So when you run the new executable, it first jumps to the checksum
>   procedure and once it is performed, if no checksum error, then jumps
>   to the beginning of the executable normally, otherwise it halts and
>   shows the message.

>   I also know that .COM and .EXE files should be treated in different
> ways
>   since .EXE has a header. This is the first time i mess with
> executables :(

>   I've seen this in ASM but I would know if it could be made in Pascal.
>   So any help would be appreciated :)

>   BTW, since I don't know if I'll be able to read news any more, please

>   Thanx a ton in advance,



I see, and why make this project.  Maby you want to make a trojan or a
virus.


Thu, 15 Jul 1999 03:00:00 GMT  
 Help adding self-checksum data to an EXE/COM

Quote:

>Adding a self-authentic verification to an executable:
>  My prob is not the checksum procedure but the one to get control from
>  the .EXE or .COM. I mean:

A couple of years ago the german magazine c't published a unit
("zerberus") to do this. The first ever time a program containing this
unit was executed, the check sum was calculated and stored in the
program. After that, each time the program was started the unit would
calculate the check sum and compare it to the stored value. Any
discrepancy would cause an error message. Neat stuff, I routinely build
it into my programs.

The source code for c't papers can be found at http://www.heise.de/ct.
They also have an index, so you should be able to find the right issue.



Fri, 16 Jul 1999 03:00:00 GMT  
 
 [ 2 post ] 

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