I have one last question about the software. How should I modify the code so instead of decrypting the files I can encypt them again using the same "CF10" signature. Thanks in advance.

Yup I did exactly that. Topic can be closed. Thx for your help!

Ok I figured out the easy part (how to compile C code in Visual Studio). But now there are two problems left: a) When I try to compile the code from my first post i get this error: "

Error 1 error C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

EDIT: Ok I've dealt with this one by adding _CRT_SECURE_NO_WARNINGS to Preprocessor Definitions! b) When I deal with the bug above how to modify code so I can "show" the program which files I want to decrypt?

Makes total sense. Let's make it Visual Studio Express 2013 for Desktop to be precise then.

To be honest I have no preferences and I can be flexible. I doubt I'll use C again in my life. I have acces to Visual Studio but isn't it only for Visual C++, C$ and VB?

Hello, Quick prerequisite: I'm graphic designer and I have no idea about programing. Long story short I want to modify some graphic files but they are encrypted. I already have the code in C for decrypting them but I have no idea how to make it into working program. Also I have no idea about C language syntax so I'm not sure if I need to modify this code so I can show the program files I need to decrypt. I would be very grateful if someone could help me with this.

#include int main (int argc, char **argv)
{
FILE *inp, *outp;
int i;
char sig[] = "CF10", *ptr;

if (argc != 3)
{
    printf ("usage: decode \[input\] \[output\]\\n");
    return -1;
}
inp = fopen (argv\[1\], "rb");
if (inp == NULL)
{
    printf ("bad input file '%s'\\n", argv\[1\]);
    return -2;
}
ptr = sig;
while (\*ptr)
{
    i = fgetc (inp);
    if (\*ptr != i)
    {
        printf ("input file sig is not 'CF10'\\n");
        return -2;
    }
    ptr++;
}
outp = fopen (argv\[2\], "wb");
if (outp == NULL)
{
    printf ("bad output file '%s'\\n", argv\[1\]);
    return -2;
}
do
{
    i = fgetc(inp);
    if (i != EOF)
        fputc (i ^ 0x8d, outp);
} while (i != EOF);
fclose (inp);
fclose (outp);
printf ("all done. bye bye\\n");
return 0;

}