KeyGenMe #2 :: C++ :: Difficulty : 3

KeyGenMe Location : KeyGenMe #2 @ Crackmes.de
Solution Location : Solution by obnoxious


My second version of KeyGenMe #2. It's coded in GNU C++. Features :
(*) NOT Packed
(*) NOT Encrypted
(*) C00L console look.

The Rules :
(*) NO Patching
(*) NO Brute-forcing

The Tasks :
1. Find a correct combination of RefID and License-Key.
2. Find the algorithm for Key and RefID calculations
3. Make a KEYGEN.
4. Write a descent tutorial. ;)

The Hints :
1. The serial can consists of the entire array of visible chracters, but
only 4 different characters would also be enough.
2. THE 4 different characters are ( 2 * Alphabets ) + ( 2 * Numbers )
3. ANY set of 4 different [ even though they too may be ( 2 * Alphabets )
+ ( 2 * Numbers ) ] characters won't work.
There exists ONLY 1 such set.
4. Most important HINT : Idea of this is inspired by bRaInF**k.

Readers, if you solve this [in a different method than obnoxious], please upload your solution to CrackMes.de.