How quantum computers will destroy and (maybe) save cryptography

More than a decade ago, I was giving an introductory presentation on quantum cryptography, as I had done many times before. I discussed the basic concepts of quantum physics, quantum computers, and quantum cryptography. I ended it with the promise that when quantum computing went mainstream that most of our current digital encryption secrets, which rely on hard-to-solve large prime-number equations, would be immediately revealed to the world.