A cryptocurrency network could continue recording valid transactions while an attacker spends funds using a private key recovered from public information. That is the central exposure identified in Europol’s new assessment of quantum computing and cryptocurrencies: the cryptography used to prove control over funds.

On October 7, 2026, Europol published Quantum Computing and Cryptocurrencies – Bridging technical expertise and decision-making, alongside a separate report on harvest-now, decrypt-later attacks. Europol’s European Cybercrime Centre (EC3) argues that preparation should begin before quantum computers capable of breaking today’s public-key cryptography become available. The timing remains uncertain, while adapting systems and coordinating upgrades will take time. Europol announcement

The cryptocurrency report’s conclusion is cautiously optimistic. Europol considers proactive adaptation the most likely outcome and challenges predictions of inevitable cryptocurrency collapse. Its assessment makes that adaptation dependent on technical changes, user participation and cooperation across decentralised networks.

Why Wallet Keys Are the Main Exposure

The report separates two security functions: maintaining the blockchain’s ledger and authorising the spending of funds.

Cryptographic hash functions help secure the ledger. Europol assesses these foundations as largely resistant to quantum attacks, particularly compared with the public-key cryptography used to authorise transactions. Its executive summary identifies cryptocurrency wallets as the primary point of exposure. That is a comparison of risks, rather than a claim that every blockchain component is immune. Report, executive summary and section III

A private key allows its holder to sign transactions. The corresponding public key lets the network verify those signatures. The security assumption is that an attacker cannot feasibly derive the private key from the public key.

Europol explains that Shor’s algorithm could overturn that assumption when run on a sufficiently powerful, fault-tolerant quantum computer. An attacker could recover a private key from an exposed public key and use it to authorise a transfer without the owner’s permission. The attack would target the mathematical protection of the key itself. Report, sections II.c and III.b

The report also highlights the public visibility of blockchain keys as a targeting opportunity. Information exposed on the ledger can remain available for future analysis. Long-lived addresses and decentralised governance could allow vulnerable assets to persist if migration is delayed.

The Risk Is Different From Decrypting Old Messages

Europol released the cryptocurrency assessment together with Harvest Now, Decrypt Later, but the two reports address different consequences of vulnerable cryptography.

In a harvest-now, decrypt-later scenario, an attacker stores encrypted information and waits for the capability to read it. The eventual harm is the loss of confidentiality: medical records, government communications or trade secrets could become readable years after collection.

For cryptocurrency holdings, Europol’s concern centres on the ability to spend funds. Recovering a signing key could enable an unauthorised transaction. Public blockchain records already expose much of the transaction history; the critical question is whether an attacker can gain control over assets that remain spendable. Report, sections III.b and IV.d

The report discusses a further scenario in which an attacker derives a private key during the interval between a transaction exposing its public key and the transaction being confirmed. It describes this as a just-in-time quantum attack. This is a future attack scenario requiring sufficient quantum capability, rather than a reported theft demonstrated in the publication.

Europol notes that exposure differs according to how funds are represented on the ledger. Its assessment therefore supports prioritising vulnerable assets during migration, rather than treating all holdings as an identical technical case.

Replacing the Algorithm Is Only Part of the Work

Europol presents post-quantum cryptography (PQC) as the main long-term response. These algorithms are designed to resist quantum attacks while running on conventional computers. The report points to NIST’s standardisation work as a foundation for the transition. Report, section IV.b

Deploying new cryptography across a decentralised network is a broader undertaking. Developers, wallet providers, exchanges, miners, node operators and users have different roles in accepting and implementing changes. There is no single authority that can revoke every compromised key or require all participants to upgrade at once.

The report identifies several practical constraints:

  • Protocol agreement: participants must coordinate changes to the rules used to authorise and validate transactions.
  • Wallet compatibility: migration can require software updates and potentially replacement hardware where existing devices cannot support the changes.
  • Transaction capacity: moving existing holdings into new forms of protection consumes blockchain capacity alongside normal transactions.
  • Larger signatures: post-quantum signatures can increase the data required for transactions, affecting block space, fees and confirmation times.
  • User participation: an available upgrade does not automatically migrate funds held under vulnerable keys.

These dependencies explain Europol’s urgency. Even if the arrival date of a cryptographically relevant quantum computer remains uncertain, the transition has operational work that cannot be completed instantly. Report, sections III.c and IV.d

What Europol Calls For

The report recommends a phased transition supported by cooperation across the cryptocurrency ecosystem. It asks decision makers and regulators to establish clear guidance for PQC adoption, blockchain projects to integrate quantum-resistant algorithms into their protocols, and wallet providers to begin testing implementations and explain the transition to users. Report, recommendations and conclusion

Europol also discusses incremental measures, including account abstraction and multisignature arrangements. It presents these as complementary approaches with implementation and adoption limitations, rather than replacements for the longer-term PQC transition. These are ecosystem-level proposals in the report; their inclusion does not establish the quantum resistance of a particular wallet or service. Report, section IV.a

Quantum key distribution and other quantum technologies receive attention too. However, Europol considers classical post-quantum cryptography more feasible for cryptocurrency protection in the near to medium term, citing the cost, infrastructure and scalability limitations of quantum-based alternatives. Report, section IV.c

Its policy guidelines call for access to current technical information, discussions on migration timing and coordinated expert work. In the conclusion, Europol emphasises testing, prioritising high-risk assets and communicating clear roadmaps.

A Preparation Warning, With an Uncertain Timeline

The report describes a credible future capability and the changes required to withstand it. It does not announce a quantum computer already breaking cryptocurrency wallet keys or provide a fixed date when that capability will arrive. Its discussion of timelines distinguishes current technical progress from the fault-tolerant computing needed for cryptographic attacks. Report, sections II.b–II.c

Europol’s assessment is that cryptocurrencies can adapt. Achieving that outcome requires the organisations maintaining protocols, custody infrastructure and wallets to coordinate their transition while users still have time to participate. The uncertainty concerns when the attacking capability will arrive; the migration challenge is already identifiable.

Sources

  • Europol, Quantum Computing and Cryptocurrencies – Bridging technical expertise and decision-making, Publications Office of the European Union, 2026. DOI: 10.2813/9406240. This article draws on the report’s executive summary, sections II–IV, conclusion and policy guidelines. Europol’s October 7 announcement introduces both publications.
  • Europol and University Carlos III of Madrid, Harvest Now, Decrypt Later, 2026. Used for the distinction between future disclosure of encrypted information and cryptocurrency signing-key exposure; see the same Europol announcement.