During World War II, the Nazis used a famously complex code machine to communicate military orders, assuming that no one would go through the effort needed to break its formidable encryption. The typewriter-like Enigma was a marvel of engineering, full of gears, dials, lights, keys, and a plugboard. But despite its clever design, the cipher was eventually broken by computers; because it relied on pseudo-random mechanical encryption, there were only a finite number of patterns possible. By the end of the war, British and American intelligence services were routinely decoding and reading intercepted Nazi messages.

Now Seth Lloyd, a researcher at MIT, has demonstrated that by exploiting the quirks of quantum physics, it is possible to build an encryption machine that is truly unbreakable.