Changing parameters in compiled program - Java

Question

I made a program, and for "protection" set some parameters. First parameter is date to wich program can work (something Trial but with fixed date), and the second one is HDD serial number (had some problems with other hardware serials) on which program works.

Now, I need to make it possible to me to change these values after compiling program. I tried adding Log in which accepts anything and executes program with default values. Only if I log in with my user/pass values, it somehow allows me to change default values. After that, by every start of program, he checks with new values I've entered earlier.

If someone understands what I want and what I tried, tell me is this possible, or is there some other and easier/better solution?

Answer 1

1. put your "constant" part in a String which will must have a fixed size
2. that string should have only ASCII code; for max flexibility I'd use a base64 encoded string, so you can put even binary encripyted data
3. compile the class
4. if you open the .class with an hexadecimal editor, you are able to see and change that string
5. edit the .class file by that hexadecimal editor, putting the new ASCII values. Keep attention not to change the size of the String

Note also that this approach can be hackable by some guys :)