EU Warns Quantum Computers Could Break Blockchain Encryption Sooner Than Expected

European Union financial supervisors assess that capable quantum computers could undermine the cryptographic systems that have long served as the security foundation of blockchain. The warning was delivered in the Autumn 2026 Risk and Vulnerability report released Wednesday by the Joint Committee of the European Supervisory Authorities (ESAs), which oversees EBA, ESMA, and EIOPA.

What sets this warning apart from earlier academic discussions is the emphasis that the threat could arrive earlier than the commercial exploitation of quantum technology itself. "The threat may materialize sooner than viable commercial applications," the authorities wrote, adding that advanced quantum computers could weaken the cryptographic systems used to secure communications, transactions, databases, and blockchain.

The report does not specify a firm deadline for when quantum computers become commercially viable. However, an IBM report cited in the document estimates the technology will be in use within four years or less. That means the window to prepare could be far narrower than many market participants assume.

The greatest risk lies in bitcoin held in Satoshi-era legacy addresses, particularly pay-to-public-key types and addresses that have been reused. In these wallet types, the public key is already exposed on the ledger, so a sufficiently powerful quantum computer could in theory derive the private key and take control of the coins. A different situation applies to many unspent bitcoin outputs, whose public keys remain protected behind cryptographic hashes and are relatively safer for now.

The structural problem is that bitcoin cannot upgrade its security the way a bank replaces its core system. Migrating to quantum-resistant signatures requires consensus across the entire network, and owners of exposed coins must move them before an attack actually occurs. This gives rise to an old dilemma: whether the community needs to freeze BTC in legacy wallets, or let it face a risk that cannot be reversed.

"The threat may materialize sooner than viable commercial applications," the European supervisory authorities warned in the report.

European authorities also highlighted the harvest now, decrypt later attack pattern, in which data collected today can be decrypted later once quantum computing power is sufficient. The European Commission is therefore pushing member states to begin the transition to post-quantum cryptography by late 2026, with a target of protection for high-risk use cases by 2030.

For Indonesia, this warning is not merely a technology issue in another part of the world. Otoritas Jasa Keuangan and Bank Indonesia are strengthening the crypto asset framework and digital payment infrastructure, while retail crypto wallet adoption continues to grow. If post-quantum standards become a requirement in cross-border financial cooperation, domestic crypto service providers will have no choice but to adjust their systems. The national banking and fintech sectors face similar demands, especially for sensitive data stored over the long term.

The question now is no longer whether quantum computers will threaten cryptography, but how quickly the global crypto ecosystem and domestic authorities prepare a safe migration path. Without agreement on the fate of coins in old addresses and without uniform post-quantum standards, the gap that opens could become a legacy of problems for decades.