"The Locked Gift": Solution
Solution to The Locked Gift, from Monday:
I put the necklace in a box, add a padlock, and send it to my wife.
She adds a second padlock and mails it back.
I remove my padlock and send her the box, and she opens it.
Dartmouth mathematician Peter Winkler writes, "This solution is not just play; the idea is fundamental in Diffie-Hellman key exchange, a historic breakthrough in cryptography."
