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Google Research said updated estimates show future quantum computers could break core cryptocurrency security sooner than earlier models suggested. In a Tuesday blog post, the company said the risk still remains years away, yet the required resources have dropped sharply. The new figures raise fresh concerns for Bitcoin wallets, live transactions, and other blockchain systems that rely on elliptic curve cryptography.
Google said most blockchain networks and cryptocurrencies depend on the 256-bit elliptic curve discrete logarithm problem, or ECDLP-256, to protect wallets and transactions. It cited a new whitepaper that compiled two recent quantum circuits. One used 1,200 logical qubits and 90 million Toffoli gates, while the other used 1,450 logical qubits and 70 million Toffoli gates.
The company said those circuits could run on a cryptographically relevant quantum computer with fewer than 500,000 physical qubits in a few minutes. That marks an estimated 20-fold reduction in the physical qubits needed to solve ECDLP-256. In turn, the revised model narrows the gap between theory and real-world attack scenarios.
Google’s white paper said the shorter execution time could let future quantum systems attack active Bitcoin transactions before network confirmation. Because Bitcoin’s average block time is about 10 minutes, the paper said such machines could carry out “on-spend” attacks during that window.
The paper said that risk extends beyond dormant wallets. Instead, it places active transactions in the mempool within reach of a sufficiently fast cryptographically relevant quantum computer. That change shifts the threat model from long-term exposure to near-real-time vulnerability.
What happens if the time needed to crack a key falls below the time needed to confirm a transaction? That question gained urgency because the new estimates suggest a nine-minute attack could fit inside Bitcoin’s normal settlement window.
The findings also drew new attention to Taproot, Bitcoin’s 2021 upgrade. Google said Taproot improved privacy and efficiency, yet it also made public keys visible on-chain by default. As a result, it removed a layer of protection that older address formats had preserved.
Google’s researchers said that the design choice could widen the pool of wallets exposed to future quantum attacks. That point added a second layer to the report. The first centered on speed, while the second focused on how many wallets could face risk.
At the same time, Google said it is changing how it releases sensitive security research. Rather than publish step-by-step details, the team used a zero-knowledge proof to validate its findings. That approach lets others verify the results without handing over a direct roadmap for misuse.
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Several industry figures said the research may mark a turning point for post-quantum planning. Haseeb Qureshi, managing partner at Dragonfly, wrote on X that the paper points to faster timelines for breaking widely used cryptographic systems. He said post-quantum readiness no longer looks theoretical.
Alex Pruden, chief executive and co-founder of Project Eleven, said the results challenge the idea that only old or poorly managed wallets face danger. He said attackers could intercept transactions before confirmation if they could crack keys within minutes. In his view, every active transaction becomes a target under that model.
Pruden also said Bitcoin cannot deploy emergency fixes quickly because any move to quantum-resistant cryptography would need years of coordination across developers, miners, and users. Meanwhile, Stefan Deiss, chief executive of The Hashgraph Group, said estimates for breaking standard encryption have fallen from billions of qubits to under a million in just over a decade. He added that Google’s plan to accelerate its post-quantum cryptography migration to 2029 should serve as a warning sign.
Google Research said quantum computers may threaten cryptocurrency security sooner than earlier estimates showed, with Bitcoin wallets and active transactions facing broader future risk. The findings also raise new concerns about Taproot exposure and the long timeline needed for post-quantum upgrades across blockchain networks.
