The quantum computer: it is not a question of whether it will happen, but when. Ever since the British physicist David Deutsch first described a quantum Turing machine – or a universal quantum computer – in 1985, the idea has never left scientists’ minds. And in twenty years, large universal quantum computers that can break cryptography will be a reality. ‘Virtually all experts agree on that. But it could well be here in fifteen years. And perhaps even in five years,’ says Simona Samardjiska, associate professor of Digital Security at Radboud University.
That quantum computer will represent a giant leap in our digital development, explains Samardjiska. ‘Whereas a classical computer works with bits that can only be 0 or 1, a quantum computer uses qubits, which can represent the state 1, 0, but it can also be any linear combination (superposition) of these two basic states.’ This allows quantum computers to evaluate functions on inputs in superposition, which in turn can lead to much faster algorithms than the ones for classical computers.
Until the sun dies
As early as the 1990s, computer scientists Peter Shor and Lov Grover developed algorithms that, when run on a quantum computer, would yield substantial speedups in certain processes. ‘Grover’s algorithm speeds up searching through unstructured data, whilst Shor’s algorithm solves a particular type of mathematical problems much faster.’ How much faster? ‘Whereas it would take current computers until the sun dies to solve certain problems, a quantum computer can solve those same problems within days, hours or even minutes.’
This means the quantum computer offers a wealth of possibilities. ‘Think of simulations of molecular behaviour as a way to develop medicines more quickly.’ Unfortunately, as with any technology, there are also less positive applications to consider. ‘Much of the traditional cryptography that underlies our digital security is vulnerable to Shor’s algorithm. From Wi-Fi security and the encryption of instant messaging apps, to logging into servers and the security of online banking.’
New security
That is why it is essential that our digital communication (for example to our bank) and stored data (such as personal or confidential data) are secured using post-quantum cryptography. Put simply, this amounts to developing even more complex mathematical problems that cannot be solved even by a quantum computer. And development is progressing rapidly: ‘At present, according to Cloudflare analysis, fifty per cent of TLS connections (secure connections on the internet) are already secured using post-quantum cryptography. In the coming years, we must secure as many important digital systems as possible in this way so that they are not vulnerable in the future.’
Furthermore, post-quantum security must already be on the agenda for future projects, Samardjiska emphasises. ‘Suppose you’re designing a new aeroplane or an electricity grid; it is very likely that these will still be in operation even in thirty, or fourty years. That won’t work if the cryptography behind its digital security can be broken in fifteen years.’
Another reason to switch to post-quantum cryptography sooner rather than later is the so-called ‘store now, decrypt later’ approach. ‘It is known that some security agencies collect encrypted traffic they cannot decrypt with today’s technology, but which they will be able to in the future with the help of a quantum computer.’
Experts from all over the world
Samardjiska and her colleagues are contributing to the development of new forms of cryptography in two ways. ‘Firstly, we are helping to design new cryptographic algorithms that a quantum computer cannot break. Secondly, we are testing how secure the cryptography developed by others is.’ The imminent arrival of quantum computers makes conducting research in digital security particularly exciting at present. ‘We’re working on this together with experts from all over the world, so I’m confident that we’ll be able to continue to keep our communication and data secure.’