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Imperfect Logic Puzzle

 
 
parados
 
  1  
Reply Wed 22 Oct, 2008 07:19 am
@glooper,
No need for a password. No need to tell Bob what is coming before he gets it.

Ship locked box with key. call to confirm, repeat til confirmed.
Ship copy of key to locked box, call to confirm, copy key and repeat til confirmed
Ship item in box with lock that fits key in received locked box.

All Eve can do is intercept every box and every key but Alice has unlimited supply of boxes and locks. Bob will get the key to the box with item. Eve can only intercept item in locked box and not send it on to prevent it from happening.
0 Replies
 
glooper
 
  1  
Reply Wed 22 Oct, 2008 07:21 am
@parados,
Eve can't open locked boxes unless she has the key.
1. A key is sent to Bob in a locked box.
2. Alice calls Bob to see if he got a locked Box. Alice knows she is talking to Bob.
3. If Bob got a locked box, then Alice sends the key to the box she sent to Bob.
4. Alice calls Bob to see if he got a key.
5. If he did not get key then go back to step 1. with new key in a locked box. Eve has unlimited boxes and locks.
6. If he did get key then ship the master box locked with lock opened by key in first box. Call Bob, ask if he got master box, then tell him to open first box, get key, unlock second box.

That actually works if you do it like this:
1. A key to the master box is sent to Bob in a locked box.
2. Alice calls Bob to see if he got a locked Box. Alice knows she is talking to Bob.
3. If Bob got a locked box, then Alice sends the key to the box she sent to Bob.
4. Alice calls Bob to see if he got a key, if so he should use that get on the first box.
5. If the first box opens and has a key in it then Alice will send the master box. If the box doesn't open (then it was intercepted by Eve) then go back to step 1 with new lock on the master box and corresponding key in a locked box. Eve has unlimited boxes and locks.

As long as Alice can change the lock on the master box before trying again, this works.

Still though, it doesn't stop a stalemate situation, whereby the box can never be opened by anybody because Eve repeatedly intercepts the boxes.
parados
 
  1  
Reply Wed 22 Oct, 2008 07:34 am
@glooper,
From the original post

Quote:
Obviously Eve could steal every package, and the problem is unsolvable. Therefore I would like to assume that while Eve can steal any given package, it is assumed that eventually she won't. Also assume that Alice has an unlimited number of boxes, locks, objects, etc.


Alice also has unlimited secret object so she can just resend that over and over in locked boxes after Bob has the key.
0 Replies
 
glooper
 
  1  
Reply Wed 22 Oct, 2008 07:41 am
@glooper,
1. Alice sends locked box with key for master box.
2. Eve intercepts it, and sends a decoy locked box, which she has the key for.
3. Once Bob has got something, Alice sends the key to the locked box.
4. Eve intercepts this key and swaps it with her own.
5. Bob opens Eve's box, which has a key in it, because Eve is clever and she knows that they do things this way.
6. Alice confirms that Bob has a key, which she thinks is for the maste box, so she sends the master box.
7. Then Eve intercepts the master box, and using the key she first intercepted, she opens the first box, which has the key for the master box, which she then opens.

Smile

This requires Eve to know that Alice will send a locked box with A KEY first. Paradoxically, if your solution is the only solution, then Eve will KNOW that Alice will send a locked box with a key in it first, which makes your solution imperfect, thereby making it not a solution at all, and thereby casting doubt on whether Alice would send such a package with the key for the master box as the first package, thereby reinforcing that Eve wouldn't know that Alice would send such a package first, and thereby making your solution good, etc.
DrewDad
 
  1  
Reply Wed 22 Oct, 2008 08:02 am
@glooper,
http://able2know.org/topic/123976-1#post-3437693

And it does not require Alice to communicate the plan to Bob ahead of time.
glooper
 
  2  
Reply Wed 22 Oct, 2008 08:12 am
@DrewDad,
Yes, but logically, if this is the solution, then Eve will figure it out too, and then she'll know to put a key in her decoy box.

I still don't know where it said that Eve could monitor their calls though.

Anyway, I'm out. peace.
0 Replies
 
FreeDuck
 
  1  
Reply Wed 22 Oct, 2008 03:41 pm
@glooper,
glooper wrote:

That actually works if you do it like this:
1. A key to the master box is sent to Bob in a locked box.
2. Alice calls Bob to see if he got a locked Box. Alice knows she is talking to Bob.
3. If Bob got a locked box, then Alice sends the key to the box she sent to Bob.
4. Alice calls Bob to see if he got a key, if so he should use that get on the first box.
5. If the first box opens and has a key in it then Alice will send the master box. If the box doesn't open (then it was intercepted by Eve) then go back to step 1 with new lock on the master box and corresponding key in a locked box. Eve has unlimited boxes and locks.

That is the proposed scenario. What did you think it was?

Quote:
Still though, it doesn't stop a stalemate situation, whereby the box can never be opened by anybody because Eve repeatedly intercepts the boxes.

That's true. But the end of the world scenario is not stalemate, it is Eve getting The Package.
0 Replies
 
 

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