For thousands of years, if you wanted to send a secret message, there was basically one way to do it. You’d scramble the message using a special rule, known only to you and your intended audience.

The original version of this story appeared in Quanta Magazine. For thousands of years, if you wanted to send a secret message, there was basically one way to do it. You’d scramble the message using a ...

So you want a smart lock. Maybe you want to lock your door without leaving the bed, or maybe you prefer key codes instead of keeping track of physical keys. Smart locks are great for these things, but ...