Revelations of the extent of government surveillance have thrown a spotlight on the security – or lack thereof – of our digital communications.
In the Nature Perspective, he and Renner describe how quantum cryptography has since progressed to commercial prospect and into new theoretical territory.
This is an interview with Professor Artur Ekert, co-inventor of quantum cryptography, about what it takes to keep secrets secret.
"As well as there being exciting scientific developments in the past few years, the topic of cryptography has very much come out of the shadows.
This arises from a mathematical discovery by Renner and his collaborator about 'randomness amplification': they found that a quantum trick can turn some types of slightly-random numbers into completely random numbers.
Applied in cryptography, such methods can reinstate our abilities to make perfectly random choices and guarantee security even if we are partially manipulated.
Over 20 years ago, Ekert and others independently proposed a way to use the quantum properties of particles of light to share a secret key for secure communication.
The key is a random sequence of 1s and 0s, derived by making random choices about how to measure the particles (and some other steps), that is used to encrypt the message.
What's more, we can even protect ourselves against adversaries with superior technology that is unknown to us.
"As long as some of our choices are not completely predictable and therefore beyond the powers that be, we can keep our secrets secret," says Renner, Professor of Theoretical Physics at ETH Zurich, Switzerland.