Are Quantum Computers about to Break Online Privacy?

A new algorithm is probably not efficient enough to crack current encryption keys—but that’s no reason for complacency, researchers say

A team of researchers in China has unveiled a technique that—theoretically—could crack the most common methods used to ensure digital privacy, using a rudimentary quantum computer.

The technique worked in a small-scale demonstration, the researchers report, but other specialists are sceptical that the procedure could be scaled up to beat ordinary computers at the task. Still, they warn that the paper, posted late last month on the arXiv repository, 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. Researchers typically estimate that it will be many years until quantum computers can crack cryptographic keys—the strings of characters used in an encryption algorithm to protect data—faster than ordinary computers.

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 who is now at the Massachusetts Institute of Technology in Cambridge, showed in 1994 how to apply the phenomena of quantum superposition—which describes the ability of atomic-sized objects to exist in a combination of multiple states at the same time—and quantum interference, which is analogous to how waves on a pond can add to each other or cancel each other out , 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 Rivest–Shamir–Adleman, or 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 quantum computer much larger than the prototypes that are available. The size of a quantum computer is measured in quantum bits, or qubits. Researchers say it might take one million or more qubits to crack RSA. The largest quantum machine available today—the Osprey chip, announced in November by IBM—has 433 qubits.