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bonanova

Locks and keys

Question

You want to send a valuable object to a friend.

You have a box to contain the object.

The box has a locking ring which is more than large enough to have a lock attached.

You and your friend have several locks with keys.

But your friend does not have the key to any lock that you have, and vice versa.

How do you do it?

Note that you cannot send a key in an unlocked box, since it might be copied.

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I like this one very much ... I heard it a few years ago ... let's see what others come up with (and how complicated this simple task can get)

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I have two questions?

1) Do you only have one box?

and

2) Do/Can you have multiple locks for one key or multiple keys for one lock?

You have only one box.

You have one key for each of your locks, but no keys for any of your friend's locks.

Your friend has one key for each of her locks, but no keys for any of your locks.

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Send it and have him cut off the lock.

Or you can handle this like a bridge crossing riddle. Send the locked box with your lock, friend sends it back with your lock and his lock, take off your lock and send it back and he can take off his lock.

Or maybe just send the locked box, confirm receipt, then send the key later.

Or have him send you a lock then send it locked with his lock.

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Or you can handle this like a bridge crossing riddle. Send the locked box with your lock, friend sends it back with your lock and his lock, take off your lock and send it back and he can take off his lock.

that's what I had in mind as well

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You have him/ her send you an unlocked lock then you put it on the box then you send it back. since he/she has the key they can open it

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You have him/ her send you an unlocked lock then you put it on the box then you send it back. since he/she has the key they can open it
Ah, but the OP specified that ...

Note that you cannot send a key in an unlocked box, since it might be copied.

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huh? maybe im misunderstanding but al im doing is having the friend send one of his locks which hasnt been closed to "me" and and then I lock the box with the lock he sent me and since it was the friends lock in the first case he could open it... maybe i misread the question.

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Yeah, I feel you KamZhiYhi. That was my #4 answer too. There's no reason you couldn't mail an unlocked lock the way the problem is set up. It's not likely to close itself in transit and then you could use it to lock up the box. Though I suppose if a key can be stolen and copied, a lock can also serve to allow a key to be copied. You could use a combination lock, but then it wouldn't be "locks and keys" - unless you define "keys" losely to include a combination of numbers.

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huh? maybe im misunderstanding but al im doing is having the friend send one of his locks which hasnt been closed to "me" and and then I lock the box with the lock he sent me and since it was the friends lock in the first case he could open it... maybe i misread the question.

Sorry, I misread it, both times. :blush:

Yes that works.

Since the OP focuses on using the box that you have, this certainly qualifies as thinking outside the box.

Kudos to both you and WB! ;)

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finally i got one right. and just so you know its really easy to unlock a combo lock you could do it the long way ie go through all combinations or listen for the clicks on the inside. not that i have done this before or anything

edit: i also thought of an even more abstract way. supposing both of you have computers you could email him a scan of your key and he could get it cut.

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Or if your friend had telekenisis he could move all the tumblers with his mind powers!
Which reminds me of the old quote:

All of you who believe in telekenesis please raise my hand.

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i would send an unlocked box to my friend.

Then he would send me back the unlocked box, with one of his locks(unlocked one) inside the box.

Then i would put my valuable stuff inside and lock it with his lock and send it back to him.

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Okay here's what they were saying which I was stumped until I saw this so I hope this is the solution:

All you need is one lock and one key for yourself and your friend has one lock and one key

Lock A and Key A are yours

Lock B and Key B are his

Solution?

1. put the parcel in the box and lock it with Lock A, send it to friend

2. friend puts Lock B on the box so now Lock A and Lock B are both on the box. He sends it back to you

3. You use your key to remove Lock A. Now just Lock B is on the box. Send it back to your friend.

4. Your friend opens Lock B and gets the parcel.

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I still think the puzzle does not clearly state that you can actually fit two locks on the box.

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The original post tells us that keys can be copied. I would copy a key to my lock. Mail the box and spare key separately. We are assuming that a locked box will get through the mail safely, and who is going to take just a key without knowing what it unlocks. Now you and your friend have a key to a lock that can be used repeatedly.

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Solution?

1. put the parcel in the box and lock it with Lock A, send it to friend

2. friend puts Lock B on the box so now Lock A and Lock B are both on the box. He sends it back to you

3. You use your key to remove Lock A. Now just Lock B is on the box. Send it back to your friend.

4. Your friend opens Lock B and gets the parcel.

Me, I would include a copy of my key along with the parcel to prevent all this hassle in the future!!

But hey, that's just me looking to learn from my past mistakes ;)

Love this puzzle BTW.

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Send a letter invitng your friend round. Give him the key to one of your locks and then send him the box locked with the valuable object inside. Then when he receives it he can unlock it with the key he has.

This does not break any specified rules does it???

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if there is no restriction on the number of locks that can used at a point

A Locks the box with his lock and the valuable object inside and sends it to B

B then locks the box again with one of his locks and sends it back to A ( two locks on the box at this time )

A then unlocks his lock and sends to B ( with only B's lock attached )

B can then open the lock and take out the valuable ( i hope it was worth all this effort :P )

WinWire Technologies Ltd.

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OR you could use a combination lock with just a number for a key and send the number in a letter or you know...like over the phone...before-hand so that they could open it when it got to them. :D

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Have your friend send you one of his locks, unlocked. (The fact pattern doesn't requries that it be in a locked box.) Lock your box with his lock, then send him the locked box. He then opens the lock with his key.

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You have only one box.

You have one key for each of your locks, but no keys for any of your friend's locks.

Your friend has one key for each of her locks, but no keys for any of your locks.

It is probley just really simple. it is probley just worded weird. Or it is sooo obviouse it is hard. O well.

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