EU Watchdogs Warn Quantum Computing Could Threaten Blockchain Encryption

The warning has renewed attention on how Bitcoin could eventually handle legacy addresses whose public keys are already exposed on the blockchain.

European financial regulators cautioned that sufficiently advanced quantum computers could weaken the cryptographic systems protecting blockchains, potentially creating a threat before the technology reaches widespread commercial use.

The warning was issued by the Joint Committee of the European Supervisory Authorities (ESAs), which comprises the European Banking Authority (EBA), European Securities and Markets Authority (ESMA) and European Insurance and Occupational Pensions Authority (EIOPA). It adds urgency to an ongoing Bitcoin debate over whether coins held in vulnerable legacy wallets should eventually be frozen.

If quantum computers become capable of breaking Bitcoin’s cryptography, about 6.9 million BTC, currently valued at roughly $586 billion, could be exposed to the threat, according to CryptoQuant.

“Threats could materialize earlier than any viable commercial application,” the authorities said in their Autumn 2026 Risk and Vulnerabilities report published Wednesday. The report warned that an advanced quantum computer could compromise cryptographic systems widely used to protect communications, transactions, databases and blockchains.

The report does not provide a specific estimate for when quantum computing could become commercially viable. However, a recent IBM report suggested the technology could enter use within four years or less.

Bitcoin associated with older Satoshi-era addresses, as well as reused addresses, may face greater exposure as quantum technology develops because their public keys can already be visible on the blockchain. A powerful enough quantum computer could potentially use that information to calculate the corresponding private key and gain control of the funds.

The same risk does not apply to every dormant Bitcoin wallet. Many unspent transaction outputs keep public keys concealed behind cryptographic hashes, making them less vulnerable at present. Older pay-to-public-key outputs and reused addresses are more exposed because their public keys are already recorded onchain.

The EU warning does not indicate that a quantum computer capable of breaking Bitcoin’s encryption currently exists. However, Bitcoin’s decentralized structure makes upgrading its cryptographic protections more complicated than changing security systems at a traditional financial institution.

A shift toward quantum-resistant signatures would require broad network consensus, while owners of potentially exposed coins would need to move their funds before quantum attacks become practical.

The European financial authorities also highlighted the risk of “harvest now, decrypt later” attacks, in which encrypted information is collected today with the expectation that it can be decoded once sufficiently powerful quantum technology becomes available.

The European Commission’s post-quantum roadmap calls on EU member states to begin the transition toward quantum-resistant systems by the end of 2026, with high-risk applications expected to have protections in place by 2030.

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