Quantum computers could break Bitcoin's encryption with fewer than 500,000 physical qubits, according to new research from Google's Quantum AI team published on March 30. That figure represents a twenty-fold reduction from previous estimates that required millions of qubits, dramatically shortening the timeline for potential attacks.
The study outlines a concrete attack method where quantum systems could derive private keys from exposed public keys during transactions. Real-time attacks could hijack in-flight Bitcoin transfers in approximately nine minutes, beating the network's ten-minute confirmation window about 41% of the time.
Approximately 6.9 million bitcoin, roughly one-third of the total supply, already sit in wallets with exposed public keys vulnerable to future quantum attacks. This includes around 1.7 million bitcoin from the network's early years and funds affected by address reuse.
Google researchers identified that Bitcoin's Taproot upgrade, introduced in 2021 to enable more efficient private transactions, may have amplified quantum vulnerabilities by changing how public keys are revealed on the blockchain. The upgrade represents a tradeoff between functionality and quantum safety.
"The company has established 2029 as a target for migration to post-quantum cryptography across its systems."
Full transition requires starting work immediately, according to researchers who stressed that while current quantum computers don't yet threaten Bitcoin's security, technological progress could accelerate risk timelines.
Google conducted the research using zero-knowledge proof methods that allow verification without exposing attack methodologies that could be misused by bad actors. The approach limits potential misuse while enabling security analysis.
Quantum computing threats extend beyond Bitcoin to Ethereum and other blockchain networks relying on similar cryptographic foundations. With cryptocurrency market projections exceeding $16 trillion by 2030, experts warn quantum vulnerabilities could become systemic risks to global financial systems.
