Est. 1998 — 27 years of woodworking knowledge
Friday Puzzler -- Kleptopia
alexy
In Kleptopia, it is known that postal employees will always steal anything of value that is not sent in a padlocked shipping box. Alan and Bob live in distant towns in Kleptopia, and Alan wants to send something to Bob. Both Alan and Bob have supplies of keyed padlocks, but neither has keys for the other's padlocks.
They have worked out a system for safely sending packages. How does their system work, to allow Alan to send a package to Bob?
Re: Friday Puzzler -- Kleptopia - Question
Larry Barrett
Is it the case that a padlock with a key is something of value, but a padlock without a key, or a key without the padlock, is not of value?
Re: Friday Puzzler -- Kleptopia - Question
alexy
No, the "of value" is not really relevant -- poor wording on my part. They will not steal a box, but will steal any contents if it is not locked.
Re: Friday Puzzler -- Kleptopia
John Veerkamp
Just have Alan cut lock from Doug's box and vice a versa. In The next exchange include a replacement lock.
Nice Solution!
alexy
and I didn't specify a non-destructive solution, so I guess you were the first to solve. But let's keep it going to see if anyone can come up with a non-destructive solution!
A non-destructive solution
alexy
But this is not the solution the puzzle author had in mind, which IMHO is more elegant. Can you find it?
Alan finds a small box with nothing in it and locks it with a padlock. On the padlock's hasp he also includes the key to a second padlock (enlarging the hole in the key if needed to fit).
Once Bob confirms receipt of that box, Alan locks his package in a box using the second padlock, which Bob can unlock using the key sent before.
Kleptopia hint
alexy
The hasp of the box latch is big enough to hold two padlocks.
Solution
Alex Y
Well, this appears to be going nowhere, so here is the solution the puzzle author had in mind:
Alan puts the package in a box, which he locks with one of his padlocks and sends the locked box to Bob
Bob adds one of his padlocks to the box and sends it back to Alan
Alan removes his padlock, and sends the box back to Bob, who is now able to open it.