Bitcoin Faces Quantum Risks as Data is Stockpiled

Security experts warn that nation-state actors are currently harvesting encrypted blockchain data in a strategy known as "harvest now, decrypt later" (HNDL), anticipating that future quantum computers will be able to crack Bitcoin's security [1]. This approach involves copying data today to exploit it once a cryptographically relevant quantum computer is developed, potentially putting up to 6.9 million BTC at risk [1].

Key takeaways

• Up to 6.9 million BTC could be vulnerable due to exposed public keys on-chain [1].
• Project Eleven estimates "Q-Day" could arrive between 2030 and 2033 [1].
• AI is accelerating quantum research, compressing the timeline for breaking encryption [2].
• Citi reports Bitcoin faces greater exposure than Ethereum due to slower governance [1].

The "Harvest Now, Decrypt Later" Strategy

Researchers describe the HNDL strategy as akin to photocopying every safe deposit box in the world while waiting for a master key to be invented [1]. The primary vulnerability lies in publicly available keys on the blockchain, specifically legacy pay-to-public-key addresses and spent unspent transaction outputs (UTXOs) [1]. Quantum algorithms, such as Shor’s algorithm, could theoretically derive private keys from these exposed public keys [1]. A Google whitepaper from March 2026 estimated that a cryptographically relevant quantum computer could break the elliptic curve digital signature algorithm protecting Bitcoin with fewer than 500,000 physical qubits [1].

Accelerating Timelines and Governance Challenges

The timeline for this threat is shrinking due to artificial intelligence, which researchers say is accelerating quantum computing development by optimizing error correction [2]. Illia Polosukhin, co-founder of NEAR Protocol, noted that AI is already being used to discover new materials and could be integral to building the next generation of quantum computers [2]. Project Eleven’s May 2026 report designates "Q-Day"—the moment quantum computers can break current encryption—as likely arriving between 2030 and 2033 [1]. However, migrating Bitcoin to quantum-resistant cryptography could take up to a decade, creating a tight margin for error [1]. A May 2026 report by Citi flagged Bitcoin as more exposed than Ethereum due to its slower governance, while other networks like NEAR and Ethereum are actively researching or implementing post-quantum migration strategies [1] [2].

Why it matters

If a significant portion of Bitcoin's supply becomes vulnerable before the network migrates, the market could face theft at scale rather than typical sell-offs [1]. The convergence of AI and quantum computing is forcing a shift from static security models to adaptive, continuously evolving processes, as developers can no longer rely on encryption remaining reliable for long periods [2]. Experts suggest investors should watch for concrete Bitcoin Improvement Proposals (BIPs) addressing quantum resistance and