Quantum computers threaten exposed private keys rather than blockchains, Europol warns

Europol warned that future quantum computers would threaten cryptocurrency wallets by deriving private keys from exposed public keys, not the blockchains themselves, and urged a phased transition to quantum-resistant security. The agency highlighted that about 6.9 million bitcoin sit in addresses whose public keys are already visible onchain and therefore could be vulnerable if a sufficiently powerful quantum computer is developed.

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Quantum computers threaten exposed private keys rather than blockchains, Europol warns

Why It Matters

The warning shifts the focus of quantum risk from blockchain immutability to wallet key exposure, meaning large, dormant holdings could be at risk unless the industry coordinates upgrades. Coordinated migration across a decentralized global network poses logistical and technical challenges that could take months of dedicated blockspace to complete.

Key Facts

Report issuer: Europol (European Cybercrime Center)
Date: Published Oct. 7, 2026
Primary vulnerability: Exposed public keys in cryptocurrency wallets (not blockchain hash functions)
Bitcoin at-risk amount: Approximately 6.9 million bitcoin in addresses with exposed public keys
Migration time estimate (study cited): Converting every UTXO to quantum-resistant format requires at least 76 days of cumulative block space; about 300 days if 25% of each block is reserved for migration

Europol’s report frames the principal quantum-era threat to cryptocurrencies as an attack on wallet keys rather than the ledger. The agency says a sufficiently capable quantum computer could derive a private key from its corresponding public key and spend the associated funds, but it emphasizes that the hash functions protecting blockchain history remain far more resistant to such attacks. Europol concluded that proactive adaptation is a more likely outcome than systemic collapse.

The report notes that many early Bitcoin addresses — including outputs whose public keys have already appeared onchain — are particularly exposed. Europol cited a figure of roughly 6.9 million bitcoin stored in addresses with visible public keys, encompassing early-era and long-dormant wallets. It warned those exposed keys cannot be made safe retroactively, creating a persistent vulnerability unless owners or the network take action.

Europol called for an immediate, phased migration to post-quantum cryptography, recommending coordinated upgrades by developers, miners, exchanges and users. The agency referenced a 2024 study estimating that converting every bitcoin unspent transaction output (UTXO) to a quantum-resistant format would consume at least 76 days of cumulative block space; if only 25% of block space is allocated to the effort, the conversion could stretch to about 300 days. A practical complication is that many candidate post-quantum signature schemes produce signatures that are 10 to 120 times larger than Bitcoin’s current ECDSA signatures, increasing the blockspace required for a migration.

Europol stopped short of forecasting when quantum machines capable of these attacks will arrive, and noted that such computers do not yet exist. The agency urged early, coordinated planning across the ecosystem to avoid a scramble once quantum capability emerges, stressing that persuading a global, decentralized network to adopt new cryptography before exposed wallets become targets is the central operational challenge.