Solutions to WU’s puzzles and riddles : Ghetto Encryption 1 (medium)

Ghetto Puzzle

I am trying to find all the solutions and put them together at a single place, So feel free to add comments and if you have a solution please do post . Cheers … 🙂

Here is the puzzles link : http://www.wuriddles.com/

Question : You want to send a valuable object to a friend securely. You have a box which can be fitted with multiple locks, and you have several locks and their corresponding keys. However, your friend does not have any keys to your locks, and if you send a key in an unlocked box, the key could be copied en route. How can you send the object securely?

Alternative, more precise phrasing: Andy and Grant are staying in different rooms in the same hotel. Andy needs to give a gold pendant to Grant, but spies are trying to assassinate Andy and Grant so neither of them can leave their room. The only way they can transfer objects is by using the bellhops. Both Andy and Grant have a safe with a large clasp that can be secured with a padlock. Both Andy and Grant have a padlock and a corresponding key. (So 1 gold pendant, 2 safes, 2 padlocks, and 2 keys.) But the bellhops are thieves. Anything that is not padlocked in the safe will be stolen by the bellhops – including any unlocked padlocks, the keys or the pendant. How can Andy transfer the gold pendant to Grant without it being stolen? (where both sides have encryption capability, and where unsecured items are taken away rather than just copied?)

My Solution : Andy will put the gold pendent in the box and then locks with Andy’s lock and passes the box to Grant. Now Grant will put on his lock and then passes back to Andy. Now Andy removes his lock and passes back to Grant and its done ….. 😛 So simple, right …. 😛


4 Responses to “Solutions to WU’s puzzles and riddles : Ghetto Encryption 1 (medium)”

  1. December 28, 2009 at 12:47 pm

    I am afraid your solution is still vulnerable to man-in-the-middle attacks. let’s see… Andy puts the gold pendent in the box and then locks it with Andy’s lock and passes the box to a bellhop (I guess the word means some kind of a delivery boy) to take it to Grant. But what if he doesn’t take it to Grant and puts his own padlock on the box, waits a few minutes and gives it back to Andy? Andy will assume that the extra padlock is Grant’s and remove his own padlock and give it back to the bellhop to take it back to Grant. The bellhop opens his own padlock and retrieves the gold pendent.

    The problem with the whole scheme is that Andy and Grant have no way in knowing that the added padlock belongs to the other party. The proper way to achieve this is by adding something equivalent to digital signatures.

  2. 2 karavi
    December 28, 2009 at 4:03 pm

    Hey dude, the concept here is not the waiter who is going to steel. The main theme is how we are going to pass on the gold pendant to the other without any complex procedures. Also this procedure is only known to Andy and Grant , but not known to the delivery boy. So once he is given the box to pass on to Grant, he don’t know that he has to pass it once again to Andy for the removal of the lock. So i guess that issue is resolved.

    Hey to put this in a better way, lets change the structure of the puzzle. Let there be a river and Andy and Grant are standing on the either side of the river. They need to pass on the box, there is a pirate in the middle of the river, who will open the box, only if the box is opened or there is a key along with the lock. And the pirate doesn’t have any locks to put on. This puzzle is asked so many times in the campus interviews, just to see how can you handle the problems in an easy way. Hope you got my point……. 😉

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