Offset writing to file binary hex

[JasonLpz]

How can i open a file and write to it while it not running. Lets say to change a value at a specific offset. i dont like write process memory thingy cuz the rogram has to be running. i want to do the change when the program isnt running.

What im trying to do is test the security of a program i have. My friend is trying to teach me how to make it hard to break into. So im trying to see if its possible .

[jim mcnamara]

Lemme see. You want to take an .EXE and write something into it?

Re-writing is trivial. Getting the re-written (patched if your intentions are honorable, hacked otherwise) to run is YOUR problem.

Here is a C fragment

FILE *out;
char *buffer="\x220\x019\x042"; // hex values - 3 bytes
long offset = 0xbb; // this is the position in the file
out=fopen"myfile.exe","rw");
fseek(out,offset,SEEK_SET); // file pointer is now somewhere in the middle of the file
fwrite(buffer,sizeof(buffer),1,out);
fclose(out);

[jim mcnamara]

PS: image file headers (.EXE files) have checksums that you will have to change. You will have to learn image file structures as well.

See PE Image Help in MSDN (Imagehlp)

[JasonLpz]

thanks this isnt for any other program crack thing or such. I want to see if i can learn why programs are so easy to crack and stuff.

[JasonLpz]

by the way the hex value why must it be 3 bytes? what if i only want to change 1 value

Originally posted by jim mcnamara
Lemme see. You want to take an .EXE and write something into it?

Re-writing is trivial. Getting the re-written (patched if your intentions are honorable, hacked otherwise) to run is YOUR problem.

Here is a C fragment

FILE *out;
char *buffer="\x220\x019\x042"; // hex values - 3 bytes
long offset = 0xbb; // this is the position in the file
out=fopen"myfile.exe","rw");
fseek(out,offset,SEEK_SET); // file pointer is now somewhere in the middle of the file
fwrite(buffer,sizeof(buffer),1,out);
fclose(out);

[CornedBee]

Doesn't matter. jim simply wrote some random values.

[JasonLpz]

oh i see thankx