public research suggests that encrypted material may eventually be unlocked by powerful computers… 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.

In the paper, which has not yet been peer-reviewed, they claim that it could break strong RSA keys — numbers with more than 600 decimal digits — using just 372 qubits. In an email to Nature on behalf of all the authors, Guilu Long, a physicist at Tsinghua University in China, cautioned that having many qubits is not enough, and that current quantum machines are still too-error prone to do such a large computation successfully. “Simply increasing the qubit number without reducing the error rate does not help.”

while Shor’s algorithm is guaranteed to break encryption efficiently when (and if) a large-enough quantum computer becomes available, the optimization-based technique could run on a much smaller machine, but it might never finish the task.