Quantum computing firm Alice & Bob estimates that about 30,000 physical qubits, 29,588 in its calculation, could break the cryptography that protects bitcoin wallets, CoinDesk reports. That is roughly 17 times fewer than the fewer than 500,000 Google estimated in March, itself a fall from earlier estimates in the millions.
The catch is time. Alice & Bob’s attack would take about 62 minutes, against a bitcoin block time that averages about 10. That is too slow to steal funds reliably from a transaction before it confirms.
The risk falls instead on coins whose public keys are already exposed, which give an attacker as long as they need. More than 6 million bitcoin sit at such addresses, according to the report.
Google’s model projected an attack of about nine minutes, but the two studies use different hardware designs and assumptions, so the gap is not like for like.
Goudarzi, quoted in the report, says there is no architectural floor. The firm has not finished working out whether more qubits could bring the runtime under ten minutes, and it expects hardware gains and falling resource needs to converge in the early 2030s.
The work is theoretical, and it comes from a firm that develops quantum hardware and so has a stake in the technology looking close. The report does not say whether it has been peer reviewed, and it does not name or link the paper.
Replacing vulnerable signatures across a decentralised network could take years, and that is the timescale nobody has yet put a date on.
