Quantum Computing and Bitcoin: How Real Is the Threat?
Quantum computers could one day break the cryptography that protects bitcoin signatures. Today they are nowhere near that point – but the topic has moved from theory to concrete proposals in Bitcoin development. Here is where things stand. First published in June 2025, updated in November 2026.
Why quantum computers matter for Bitcoin
Bitcoin uses digital signatures to prove who may spend coins. Their security rests on the fact that a private key cannot be calculated from a public key with today's computers. A sufficiently large quantum computer could do exactly that. The risk therefore concerns coins whose public key is already visible on the blockchain – for example in very old address formats, in Taproot outputs or in addresses that have been reused.
How far away is the danger?
Google's "Willow" chip, presented in December 2024, has 105 physical qubits. Google itself says it cannot break modern cryptography. That would require machines that are far larger and more stable than anything that exists today. How many years that will take is disputed – but the transition to new cryptography in a decentralised network also takes years, which is why developers are starting now.
Large investors are taking the issue seriously as well: in May 2025, BlackRock added quantum computing as a risk factor to the documents for its Bitcoin ETF.
How many coins are exposed?
A report by the Human Rights Foundation from October 2025, cited by Forbes, estimates that about 1.72 million BTC sit in very early address formats and would be highly vulnerable. Many of these coins are probably lost or dormant – including around one million coins attributed to Satoshi Nakamoto. A further 4.49 million BTC are also considered vulnerable, but their owners could protect them by moving them to new address types. Together, that is roughly a third of all bitcoin by value.
What developers are doing
In 2025, a developer proposed forcing vulnerable coins into quantum-safe addresses via a hard fork – a controversial idea that would have frozen coins not moved in time. A more cautious step followed on 11 February 2026: BIP 360 was added to the official repository of Bitcoin Improvement Proposals. It proposes a new output type, Pay-to-Merkle-Root (P2MR), which does not expose the public key on-chain.
Important: being added to the repository does not mean approval or activation. BIP 360 changes nothing for existing coins today. Real post-quantum signatures would require further soft forks, and they are considerably larger than today's signatures – which raises questions about block space and fees.
What you can do today
- No panic: There is currently no quantum computer that can steal bitcoin. There is no need to act hastily.
- Avoid address reuse: Use a new receiving address for every payment. Modern wallets do this automatically.
- Follow your wallet provider: When quantum-safe address types become available, reputable wallets will announce how to migrate.
- Beware of scams: Offers of "quantum-safe bitcoin" or urgent requests to move your coins to a specific address are a classic fraud pattern.
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