Are quantum computers about to break online privacy? – Nature.com
A quantum computer at IBM’s Thomas J. Watson Research Center.Credit: Connie Zhou for IBM
A team of researchers in China has unveiled a technique that — theoretically — could crack the most commonly used types of digital privacy using a rudimentary quantum computer.
The technique worked in a small-scale demonstration, the researchers report, but other experts are sceptical that the procedure could scale up to beat ordinary computers at the task. Still, they warn that the paper, posted late last month on the arXiv repository1, is a reminder of the vulnerability of online privacy.
Quantum computers are known to be a potential threat to current encryption systems, but the technology is still in its infancy and researchers typically estimate that it will be many years until they can be faster than ordinary computers at cracking cryptographic keys.
Researchers realized in the 1990s that quantum computers could exploit peculiarities of physics to perform tasks that seem to be beyond the reach of ‘classical’ computers. Peter Shor, a mathematician now at the Massachusetts Institute of Technology in Cambridge, showed in 19942 how to apply the phenomena of quantum superposition and interference to factoring integer numbers into primes — the integers that cannot be further divided without a remainder.
Shor’s algorithm would make a quantum computer exponentially faster than a classical one at cracking an encryption system based on large prime numbers — called RSA after the initials of its inventors — as well as some other popular cryptography techniques, which currently protect online privacy and security. But implementing Shor’s technique would require a much larger quantum computer than the prototypes available. The size of a quantum computer is measured in quantum bits, or qubits; researchers say it might take a million or more qubits to crack RSA. The largest quantum machine available today — the Osprey chip announced in November by IBM — has 433 qubits.
Shijie Wei at the Beijing Academy of Quantum Information Sciences and collaborators took a different route to beat RSA, based not on Shor’s but on Schnorr’s algorithm — a process for factoring integer numbers devised by mathematician Claus Schnorr at Goethe University at Frankfurt, Germany, also in the 1990s. Schnorr’s algorithm was designed to run on a classical computer, but Wei’s team implemented part of the process on a quantum computer, using a procedure called quantum approximate optimization algorithm, or QAOA.
In the paper, which has not yet been peer-reviewed, they claim that it could break strong RSA keys — numbers with more than 600 decimal digits — using just 372 qubits. …….