Europol, the law enforcement agency of the European Union, released a report on Wednesday stating that quantum computers are not expected to break blockchain networks in the foreseeable future. However, the agency warned that Bitcoin wallets with exposed public keys face significant risks as quantum technology advances.
Quantum risk targets public key wallets
The European Cybercrime Center, a division under Europol specializing in cyber threats, highlighted that wallets whose public keys are publicly visible on blockchains are “the primary point of exposure to quantum threats.” Wallets sign transactions using private keys, while the network verifies them through public keys. In theory, a powerful enough quantum computer could use an exposed public key to deduce the corresponding private key, enabling an attacker to spend those funds.
Europol emphasized that there is currently no cryptographic solution for users whose wallet public keys are already exposed. The report advised a “pre-emptive migration,” meaning users should transfer their assets to new wallets that have not yet revealed their public keys to the blockchain.
Any wallet with an exposed public key may need to move its funds before practical quantum attacks become possible. The best defense is proactive migration to more secure wallets before new attack vectors appear.
As of May 2024, an estimated 6.04 million BTC, or about 30.2% of the circulating supply, are held in addresses with public keys already revealed on-chain. Another estimate cited in the report places this figure closer to 6.9 million BTC, accounting for early public-key-based outputs and long-dormant coins from the earliest years of Bitcoin.
Opinions within the Bitcoin community differ over whether to implement measures that would freeze coins associated with Satoshi-era wallets, some of which have remained untouched for years.
Hash functions prove resilient, post-quantum updates underway
Europol’s analysis found that the cryptographic hash functions binding blockchain blocks together and protecting mining activity are not vulnerable to quantum attacks under current technology. According to the report, a quantum computer would need approximately 2^128 quantum operations to break a 256-bit hash function, a level of effort described as “astronomically high with foreseeable technology.”
Despite these reassurances for blockchains themselves, the report stated that adaptation, rather than collapse, is the likely outcome for cryptocurrency systems. Europol concluded that, “cryptocurrencies will not collapse due to quantum computing,” but users and networks must proactively upgrade to post-quantum security standards as a precaution.
Switching to post-quantum infrastructure presents challenges
Europol cited research from 2024, indicating that migrating all Bitcoin wallets with exposed public keys to quantum-resistant formats could take a combined downtime of at least 76 days. If only 25% of each block’s capacity is used for this migration, the process could be extended by another 300 days.
| Migration Approach | Estimated Duration |
|---|---|
| Full migration at maximum capacity | 76 days |
| Migration using 25% of each block | ~376 days |
Adoption of post-quantum signatures, such as those being standardized by the US National Institute of Standards and Technology (NIST), faces technical hurdles. These new signatures are 10 to 120 times larger than the elliptic curve signatures currently used by Bitcoin, creating potential challenges for network capacity, transaction fees, and confirmation speeds.
Mini dictionary: NIST (National Institute of Standards and Technology) is a US federal agency responsible for developing technology, metrics, and standards, including the standardization of post-quantum cryptographic algorithms.
Additional research, including a report jointly produced with the University Carlos III of Madrid, explored the concept of “Harvest Now, Decrypt Later,” where attackers collect encrypted data today with plans to decrypt it using future quantum computers. Europol noted it has not found substantial evidence that this method poses a significant threat at present. However, information with long-term value is considered the most likely target for such schemes.
Responses from regulators and the crypto industry
The European Commission has reportedly encouraged member states to migrate critical systems to post-quantum security by the end of 2026 for standard applications, and before 2030 for high-risk setups.
The foundational post-quantum infrastructure for Ethereum is targeting a rollout by 2029. Meanwhile, Bitcoin developers are examining a possible soft fork proposal known as BIP-360 to enhance security against quantum threats.
A separate report referenced an experiment by more than 100 researchers who used AI to reduce the resource requirement for a quantum attack on Bitcoin by 86.1%. The type of quantum computer capable of carrying out such an attack does not yet exist, and Europol gave no indication as to when one might become practical.
