Google researchers have published findings suggesting that the cryptographic protections underpinning Bitcoin and Ethereum could be compromised with significantly fewer quantum computing resources than previously thought. Earlier estimates placed the required number of physical qubits in the millions, but the new paper indicates that fewer than 500,000 physical qubits may be sufficient. The researchers also estimate that roughly 1,200 to 1,450 high-quality qubits would be needed to carry out practical attacks.
One of the more striking scenarios outlined in the paper involves real-time attacks on in-flight Bitcoin transactions. According to the researchers, a quantum attack could potentially hijack a transaction in approximately nine minutes, which would be fast enough to beat the network’s confirmation process around 41% of the time. This finding raises concerns about the window of vulnerability that exists between when a transaction is broadcast and when it is confirmed on the blockchain.
The paper also identifies a pool of approximately 6.9 million bitcoin that are already considered exposed due to the visibility of their associated public keys. When a public key is known, it becomes a potential target for a sufficiently powerful quantum computer attempting to derive the corresponding private key. The researchers note that this represents a meaningful portion of circulating supply that could be at risk under future quantum conditions.
Bitcoin’s Taproot upgrade is highlighted as a factor that may expand the number of vulnerable wallets. Taproot makes public keys visible by default, which, while offering other technical benefits, increases the surface area for potential quantum attacks. The researchers suggest this development makes the case for earlier migration to post-quantum cryptographic standards more pressing.
Despite the urgency of the findings, Google stresses that quantum attacks on cryptocurrency networks are not yet imminent. The current state of quantum hardware remains far from the thresholds described in the paper, and significant engineering challenges would need to be overcome before such attacks become feasible. The researchers frame their work as a forward-looking assessment intended to inform preparation rather than signal immediate danger.
The paper serves as a call to action for the cryptocurrency community to begin transitioning toward post-quantum cryptographic protocols before capable quantum hardware becomes available. Google’s researchers urge that migration efforts start earlier than previously planned, given the revised and lower resource estimates now on record. The findings are expected to contribute to ongoing discussions within both the cryptography and blockchain development communities about long-term security planning.
Originally reported by CoinDesk.
