Google's Quantum AI team published research on Tuesday claiming that breaking Bitcoin (BTC) and Ethereum (ETH) cryptography would require fewer than 500,000 physical qubits — roughly 20 times less than previous estimates — raising fresh concerns about how soon quantum computers could threaten blockchain security.
Google Quantum Research
The whitepaper and accompanying blog post detail a method for cracking 256-bit elliptic curve cryptography, the mathematical system that secures most blockchain wallets and transactions. Google's team estimated that a superconducting quantum processor could execute the attack in minutes.
That timeline assumes hardware capabilities consistent with some of Google's existing flagship processors.
Rather than targeting wallets at rest, the research models a live attack scenario. A quantum adversary could calculate a private key from a briefly exposed public key in roughly nine minutes. That would give an attacker a 41% chance of beating Bitcoin's 10-minute block confirmation window.
Ethereum may face slightly less exposure on this front, since its transactions confirm faster. But the broader implication is clear: the resource threshold for a quantum attack has dropped significantly.
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Taproot Exposure Risk
The findings put Bitcoin's 2021 Taproot upgrade in a harsher light. Taproot improved privacy and efficiency but began exposing public keys on-chain by default. It removed the hash-based protective layer that older address formats provided.
That change widened the pool of quantum-vulnerable coins to an estimated 6.9 million BTC. The figure includes Satoshi-era holdings and heavily reused addresses — roughly one-third of Bitcoin's total supply.
