Quantum attack on bitcoin keys may need only about 30,000 qubits, 17 times fewer than Google's estimate
French quantum firm Alice & Bob says a machine of roughly 30,000 physical qubits could crack an exposed bitcoin key in about 62 minutes. More than 6 million BTC sits at addresses with exposed public keys.
A new estimate from quantum computing company Alice & Bob says breaking a bitcoin private key could take about 29,588 physical qubits, roughly 17 times fewer than the under-500,000 Google estimated in March 2026, CoinDesk reported on Thursday 29 October. The two studies use different hardware designs and assumptions, so the comparison is not like for like.
The numbers
| Alice & Bob (Oct 2026) | Google (Mar 2026) | |
|---|---|---|
| Physical qubits needed | about 29,588 | under 500,000 |
| Time to break one key | about 62 minutes | about 9 minutes |
Today's largest quantum computers are far from either figure, and the work is theoretical. But the trend matters: estimates have fallen from millions of qubits a few years ago to tens of thousands.
Which bitcoin is at risk
The attack uses Shor's algorithm to work out a private key from a public key. At 62 minutes it is too slow to hijack a normal transaction, since a bitcoin block is mined about every 10 minutes. The real exposure is coins sitting at addresses whose public keys are already visible on the blockchain, such as old pay-to-public-key outputs and addresses that have been reused. More than 6 million BTC sits behind exposed public keys, CoinDesk said; at Thursday's price of about $80,870 that is roughly $485 billion.
Dahmun Goudarzi, Alice & Bob's senior cryptanalyst, said: "Yes, it becomes of utmost importance that migration starts now," and "There is no architectural floor." He expects better hardware and falling requirements to meet in the early 2030s. His team has not yet worked out whether more qubits could push the attack under 10 minutes.
What it means for you
Crypto trading is popular in Pakistan even though the SBP has never licensed it as legal tender. If you hold bitcoin:
- Do not reuse addresses. Send each payment to a fresh address from your wallet, so your public key is not exposed while coins still sit there.
- Keep coins in modern address types (addresses starting bc1) that reveal the public key only when you spend.
- Watch for wallet updates as developers move toward quantum-resistant signatures, a change CoinDesk notes could take years across a decentralised network.
Follow the price in rupees on our bitcoin data page.
Frequently asked questions
- Can a quantum computer break bitcoin?
- Not yet. Alice & Bob estimated in October 2026 that about 30,000 physical qubits could break an exposed bitcoin key in about 62 minutes, but no machine that size exists, and the company expects the risk to become real in the early 2030s.
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