[keygenme] KeyGenMe #5/#6 .NET

[CodeExplorer]

KeyGenMe #5. It's coded in VB.NET. Features :

(*) NOT Packed

(*) NOT Encrypted

(*) Kool GFX 'n' SFX

The Rules :

(*) NO Patching

(*) NO Brute-forcing

The Tasks :

1. Find the algorithm for the computations involved.

2. Try to get Status as ":-)".

3. Make keygen to VALID Key for ANY name. Please note that VALID KEYS EXIST FOR ALL NAMES.

Keygens able to generate multiple keys for each name will be preferred.

KeygenMe #5.zip

KeygenMe #6.zip

[CodeExplorer]

KeyGenMe #5 description

So, the main goal of crackme is win the game. As we knew in the Tic-tac-toe game (3x3 grid) the best strategy of both parties leads to a draw. So, to beat the computer there must be a weakness in algorithm. And there it is! If we put "X" in center, the computer always bring to a draw; If we put "X" in any side but not corner, the computer always win; But if we put "X" in corner, there is one weakness that helps us win:

After we put "X" in corner, computer always put "O" in center:

X - -

- O -

- - -

Then, if we want win, the best way is put "X" in an opposite corner:

X - -

- O -

- - X

After this, the best computer move is put "O" at any side (not corner!), but in crackme it moves into corner:

X - O

- O -

- - X

At this point we have already won . Just put "X" in empty corner and there is fork

X - O

- O -

X - X

Now, computer can't do anything to win or draw

This was the main logic. Read the complete solution (in my box or from crackmes.de) for further details.