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.
