Europol: Exposed Private Keys Face Greater Quantum Risk Than Blockchains

Europol is urging the crypto industry to start preparing for the potential arrival of quantum computing, warning that exposed wallet keys could present a greater vulnerability than the blockchains themselves.

In a report published Wednesday, the European Union’s law enforcement agency said cryptocurrency wallets are likely to be the primary target of future quantum attacks. The underlying blockchain networks, by comparison, are not expected to face the same level of immediate risk.

Quantum computers capable of executing these attacks do not yet exist, and Europol did not offer a prediction for when they might become capable of doing so. The agency instead emphasized early preparation, saying “proactive adaptation, rather than systemic collapse, is the most likely outcome.”

Europol recommended that the industry begin a phased transition to quantum-resistant systems, including wallet upgrades and post-quantum cryptography. It also called for coordination among developers, miners, exchanges and users.

Bitcoin researchers and institutions are increasingly using 2029 as a target for having credible quantum-resistant migration strategies in place. IBM said in July that it expects quantum computing to generate significant commercial revenue within the next two to four years.

Europol’s European Cybercrime Center warned that a sufficiently powerful quantum computer could potentially calculate a private key from a publicly exposed key, allowing an attacker to authorize transactions involving the associated funds.

Exposed Keys Could Put Dormant Bitcoin at Risk

The report draws a distinction between two types of cryptographic protection. Hash functions that secure blockchain history and support activities such as Bitcoin mining are considerably harder for quantum computers to attack than the public-key cryptography used to control wallets.

“Cryptocurrencies will not collapse due to quantum computing,” Europol said. The greater concern is the potential theft of assets from vulnerable wallets, rather than a quantum computer rewriting the Bitcoin blockchain.

Bitcoin addresses from the network’s earliest period are especially relevant. Often referred to as the “Satoshi era,” these addresses include holdings whose public keys have already been exposed on-chain. If quantum computers become sufficiently powerful, attackers could potentially use those public keys to derive their corresponding private keys.

Europol estimates that around 6.9 million BTC are stored in addresses with exposed public keys. The figure includes early pay-to-public-key outputs and a large number of coins that have remained inactive for long periods.

Once a public key has been exposed, Europol said the associated risk cannot be removed retroactively. This has intensified debate over how the Bitcoin community should handle Satoshi-era holdings, including whether potentially vulnerable coins should eventually be frozen as quantum technology advances.

Bitcoin Migration Could Consume Months of Block Space

Another challenge is moving existing Bitcoin holdings into quantum-resistant formats. Europol cited a 2024 study estimating that migrating every Bitcoin unspent transaction output, or UTXO, could consume at least 76 days of cumulative block space.

If the migration were limited to 25% of each block, the study estimated that the process would take approximately 300 days.

The transition could also make transactions larger. Europol said post-quantum signature schemes can be 10 to 120 times larger than Bitcoin’s current Elliptic Curve Digital Signature Algorithm, or ECDSA, signatures.

ECDSA is the cryptographic system used to verify Bitcoin ownership and authorize transfers.

That means Bitcoin’s quantum challenge is not simply a matter of developing new cryptography. The network must also coordinate a migration involving a decentralized ecosystem of developers, miners, exchanges, wallet providers and users before quantum computers become powerful enough to exploit exposed keys.