Hello, dear readers! Welcome back to my blog, where I share with you some of the most interesting and challenging puzzles I come across. Today, I have a very romantic puzzle for you, involving a ring, a lock box, and some padlocks. Sounds intriguing, right? Let me tell you the story. Imagine you want to send your beloved a ring using a mail service that is notorious for opening packages and stealing valuables. To ensure the ring arrives safely it must be sent in a lock box, such as the one shown on the right, which has five holes for padlocks. (A padlock in any of the five holes will lock the box securely.) You and your beloved have five padlocks each. You also have the keys for your own padlocks, but you don’t have the keys for each other’s padlocks. If you have unlimited money for postage, how are you able to send your beloved the ring? This puzzle is called the SAFE PACKAGE Problem, and it is a classic example of a logic puzzle involving cryptography. Cryptography is the scienc...