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.
Nic Carter's Warning
Google set 2029 as an internal deadline for post-quantum migration earlier this month. Researchers have warned that even once the hardware arrives, the actual migration process will take years.
Coin Metrics co-founder and Bitcoin advocate Nic Carter flagged the urgency on X. He highlighted a separate paper released the same day from Oratomic, Caltech and UC Berkeley, showing quantum computers could break cryptographic systems with just 10,000 reconfigurable atomic qubits.
Carter called it potentially more alarming than Google's own findings.
Traders should monitor Taproot adoption metrics, progress on BIP-360-style upgrade proposals and whether Bitcoin developers commit to a concrete migration timeline as Google's 2029 target draws closer.
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