Homomorphic encryption: computation on encrypted databases without ever decrypting them. An important step that should eventually allow even the most privacy focused institutions off-loading some of their data processing into public clouds.
Alice hands bob a locked suitcase and asks him to count the money inside. “Sure,” Bob says. “Give me the key.” Alice shakes her head; she has known Bob for many years, but she’s just not a trusting person. Bob lifts the suitcase to judge its weight, rocks it back and forth and listens as the contents shift inside; but all this reveals very little. “It can’t be done,” he says. “I can’t count what I can’t see.”