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If you need to send a message in a box to a person so that no one can intercept it and get the message, how do you do so if you have a padlock and key and they have a padlock and key

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This solution has the box being locked anytime it's in transit, and does not require any exchange of keys:

A puts the message in the box, padlocks it, and sends it to B. B padlocks the box, and sends it back to A. A unlocks their padlock and sends the still-locked box back to B. B unlocks their padlock and opens the box.

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  • $\begingroup$ The first thing we're going to do is to rotate all those discs as far clockwise as they'll go. Then, I'm going to get the pick Bosnian Bill and I made.. $\endgroup$
    – Bass
    Feb 23 at 20:41

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