Question

I mean, I always was wondered about how the hell somebody can develop algorithms to break/cheat the constraints of legal use in many shareware programs out there.

Just for curiosity.

Answer 1

Apart from being illegal, it’s a very complex task.

Speaking just at a teoretical level the common way is to disassemble the program to crack and try to find where the key or the serialcode is checked.

Easier said than done since any serious protection scheme will check values in multiple places and also will derive critical information from the serial key for later use so that when you think you guessed it, the program will crash.

To create a crack you have to identify all the points where a check is done and modify the assembly code appropriately (often inverting a conditional jump or storing costants into memory locations).

To create a keygen you have to understand the algorithm and write a program to re-do the exact same calculation (I remember an old version of MS Office whose serial had a very simple rule, the sum of the digit should have been a multiple of 7, so writing the keygen was rather trivial).

Both activities requires you to follow the execution of the application into a debugger and try to figure out what’s happening. And you need to know the low level API of your Operating System.

Some heavily protected application have the code encrypted so that the file can’t be disassembled. It is decrypted when loaded into memory but then they refuse to start if they detect that an in-memory debugger has started,

In essence it’s something that requires a very deep knowledge, ingenuity and a lot of time! Oh, did I mention that is illegal in most countries?

If you want to know more, Google for the +ORC Cracking Tutorials they are very old and probably useless nowdays but will give you a good idea of what it means.

Anyway, a very good reason to know all this is if you want to write your own protection scheme.