Quantum computers are a fundamentally different sort of computer that take advantage of aspects of quantum physics to solve certain sorts of problems dramatically faster than conventional computers can. While the Quantum Computers will be very useful in various ways, they can create problems in some ways. Specifically, if large quantum computers can be built then they may be able to break the asymmetric cryptographic primitives that are currently used in TLS, the security protocol behind HTTPS.
Quantum computers exist today but, for the moment, they are small and experimental, containing only a handful of quantum bits. It’s not even certain that large machines will ever be built, although Google, IBM, Microsoft, Intel and others are working on it. Adiabatic quantum computers, like the D-Wave computer that Google operates with NASA, can have large numbers of quantum bits, but currently solve fundamentally different problems.
However, a hypothetical, future quantum computer would be able to retrospectively decrypt any internet communication that was recorded today, and many types of information need to remain confidential for decades. Thus even the possibility of a future quantum computer is something that we should be thinking about today.
The study of cryptographic primitives that remain secure even against quantum computers is called “post-quantum cryptography”. Google has announced an experiment in Chrome where a small fraction of connections between desktop Chrome and Google’s servers will use a post-quantum key-exchange algorithm in addition to the elliptic-curve key-exchange algorithm that would typically be used. By adding a post-quantum algorithm on top of the existing one, Google is able to experiment without affecting user security. The post-quantum algorithm might turn out to be breakable even with today’s computers, in which case the elliptic-curve algorithm will still provide the best security that today’s technology can offer. Alternatively, if the post-quantum algorithm turns out to be secure then it’ll protect the connection even against a future, quantum computer.
Google’s aims with this experiment are to highlight an area of research that it believes to be important and to gain real-world experience with the larger data structures that post-quantum algorithms will likely require. There are many post-quantum algorithms available. Google selected a post-quantum algorithm named “New Hope” for this experiment.
