Personal data
stored on electronic health cards needs to be still secure in many years’ time.
However, once
quantum computers exist, this is no longer guaranteed for the asymmetric
techniques that
are currently in use. © Roberto Schirdewahn
Interview with Tim Güneysu
(December 20, 2015) Prof Güneysu, together with your group, you
are developing novel encryption techniques that even shall resist attacks by
quantum computers. However, a quantum computer does not exist yet.
That’s true. Still, security must always think in terms of
the future. These days we know two flavours of cryptography, namely the
symmetric and asymmetric cryptography. The latter are required for the
implementation of advanced security services such as are deployed in a majority
of systems. Take the log-in to Amazon as an example, where you will likely
submit critical information such as your credit card information. In the first
step, a secret key has to be negotiated between the user and Amazon’s server
before the encrypted data transmission can commence. And such transactions take
place millions of times each day.
Currently, two different kinds of asymmetric methods are in
use in virtually all practical systems, and we already know that both would be
broken in the era of quantum computers. It is an open question when
sufficiently powerful quantum computers will become available. But we have to
be ready. So alternative systems must be established in the market by that
time. Moreover, we must prevent the encrypted data of today to be
retrospectively revealed with the support of quantum computers that might be
around in some years.
How do cryptographic
techniques that protect from quantum computers differ from established
techniques?
Quantum computers enable a novel paradigm of computation.
Depending on the application, they will boast a computing power that is much
higher than that of current computers. Hence we need techniques of post-quantum
cryptography, i.e. asymmetric cryptographic techniques that are safe from
quantum computer attacks. Those rely on particularly difficult mathematical
problems that are not expected to be solved more efficiently even if the
computational model of a quantum computer is deployed. Unfortunately, the
instances of those problems are often not that difficult to solve unless they
operate with large parameters, what leads to extremely long cryptographic keys.
In our EU project Post-Quantum Cryptography, we focus on four existing
categories of cryptographic techniques in this context that would constitute a
suitable replacement of current asymmetric cryptographic techniques.