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Topic: ghetto encryption 1 (Read 6078 times) |
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buddha
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Re: ghetto encryption 1
« Reply #25 on: Dec 31st, 2002, 11:15am » |
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The riddle states:
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?
it doesn't state anything in this version about any attackers or adversaries. why not just hand deliver the object and forget about the locks.
in the alternative version:
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?)
why not send your lock, un-locked, in your box to your friend with a note stating. Please place any objects in box and lock with enclosed lock, then send back, and vise versa.
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Johno-G
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Could God create a wall that he could not jump?
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Re: ghetto encryption 1
« Reply #26 on: Jan 10th, 2003, 2:49am » |
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buddah, the problem states that any unlocked padlocks would be stolen by the thieves, so any attempt made by Andy to send his unlocked padlock to Grant would only result in it being stolen.
This also assumes that you don't need to use the key to LOCK the padlock, as with some locks.
I think the solution first posted is the most accurate:
Andy places the pendant in the safe and secures the safe closed with his lock, and then sends it to Grant, who then uses his padlock on the safe (so it is now secured with two padlocks), and sends it back to Andy. Andy unlocks his own padlock, and sends it back to Grant. The safe now only has his lock on it, so he will be able to open it and get the pendant.
(however, this leaves one of the safes unused, and so I'm wondering if there's a flaw in the logic somewhere, or else why is it stipulated that there are TWO safes??)
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Adam Wygle
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Why does it matter if the key gets copied after the items have been recieved?
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Fisher
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"(where both sides have encryption capability, and where unsecured items are taken away rather than just copied?)"
They keys/locks do not get copied. They get STOLEN.
Send pendant in locked box to your friend.
Friend puts his lock on YOUR box as well and sends it back.
You unlock your lock from the box (so now only his remains) and send it back.
He unlocked his lock, opens the box, and takes the pendant.
At all times in transit the box was locked (sometimes double locked!)
Why cant you noobs understand?
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