On the top, you can see 4 cards labelled ABCD. Now, pick a whole number ranging from 0-15.
Got it? Yes.
Is it on card A? Yes.
Is it on card B? No.
Is it on card C? No.
Is it on card D? Yes.
The number you picked is 9.
Now, look back at the cards, try to figure out how I found out your number.
Figured it out yet?
No?
This is how it works:
1. Player picks one number between 0-15.
2. The number is on card A.
3. The number is not on card B.
4. The number is not on card C.
5. The number is on card D.
Okay, now that I have written all the clues I have, how can those clues help??
Clue number 1 : The number is between 0-15 (16 possibilities).
Clue number 2 : The number is on card A (8 possibilities left, since there are only 8 numbers on card A. Zero is also eliminated since it's not on card A).
Clue number 3 : The number is not on card B (Eliminate all numbers on card B[4,5,6,7,12,13,14,15]).
Clue number 4 : The number is not on card C (Eliminate all numbers on card C[2,3,6,7,10,11,14,15]).
Numbers Eliminated : 0,2,3,4,5,6,7,10,11,12,13,14,15
Numbers Left : 1, 8, 9
Clue number 5 : The number is on card D.
Conclusion : Find the number (from the "numbers left" list) that is on both card A and card D.
It's 9. That's how it actually works.
So, what is the relation between this game and computer security?
As you can see, from 4 simple yes/no answers, we can get so much information, enough to guess(or in the victim's mind, "PREDICT") his number.
Therefore, you should think twice before answering any questions on the internet or elsewhere. It may lead to something harmful or dangerous, such as identity theft.
Note:
There is another method that involves memorizing answers to predict/guess player's number quickly, as soon as he/she gives us his/her fourth answer. However, I will not include this here, since this post mainly focuses on Computer Security, not algorithms.
Thank you for reading.
Cyber Frost
