CRC CheckSum Problem ( maybe )

[JMI]

How2Crack:

Giving you the answer will not teach you anything. What you are most likely dealing with is code that does a checksum on all the bytes in the program and, if you change a single byte, you change the sum that it is checked against.

What you need to do is read up on how CRC is checked. In broad strokes, the program needs to access and read the file, probably in memory. Frequestly, after the code checks the sum of the bytes, it is compared against a number that is hard coded somewhere in the file. When you can locate that "target number" the checksum becomes meaningless, because you can change what total the files is compared against and reset it to equal the actual total given after your changes.

So you need to learn about CRC and the API's that are used to perform such a check. This gives you the breakpoint to intercept so you can be in the middle of the check.

Go here:

hxxp://www.anticrack.de/modules.php?op=modload&name=Topics&file=index

and read some of the articles in the section titled:

RCE - CRC (Cyclic Redundancy Code)

and you'll be on your way. After you'd done your homework, come back and ask specific questions.

Regards.