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.