Google quantum research shows that quantum computing may need far fewer resources to break the cryptography used in Bitcoin security and Ethereum security than many earlier estimates suggested.
The study said a future quantum machine could break the 256 bit elliptic curve cryptography used across major blockchains with fewer than 500,000 physical qubits.
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The updated estimate matters because elliptic curve cryptography protects private keys tied to blockchain wallets and transactions.
According to the paper, the new result reflects a 20 fold reduction in the number of physical qubits needed to solve the 256 bit elliptic curve discrete logarithm problem, also called ECDLP 256.
The researchers tested two compiled quantum circuits on a superconducting qubit model described as a cryptographically relevant quantum computer. As a result, the findings brought new attention to the long term crypto quantum threat facing public key based blockchain systems.
Google quantum research lowers the qubit estimate
The new Google quantum research said fewer than 500,000 physical qubits could be enough to attack ECDLP 256 under current hardware assumptions. That is a much lower figure than earlier estimates often discussed in the industry.
The study focused on circuit design and hardware modeling. Because of those changes, the researchers reported a 20 fold reduction in the qubit count needed to break the cryptography used in Bitcoin and Ethereum.
This estimate does not mean such a machine exists today. However, it changes the scale of the problem. Therefore, the discussion around quantum computing and crypto quantum threat is moving closer to practical blockchain security planning.
Bitcoin security faces a short attack window
The paper said a quantum computer could recover a Bitcoin private key in about 9 minutes in a theoretical attack model. In another estimate, the time could be about 12 minutes.
That timing matters for Bitcoin security because the network’s block time is about 10 minutes. When a public key is exposed during a transaction, a quantum attacker may have a narrow window to derive the private key and try to steal the funds before confirmation.
The researchers described this as an on spend attack. They wrote,
“We should estimate the time required to launch an on-spend attack starting from this primed state at the moment the public key is learned to be roughly either 9 minutes or 12 minutes.”
In this model, speed is central to the attack.
Ethereum security faces at rest attack risk
The paper said Ethereum security faces a different kind of quantum risk. In this case, the threat is not limited to a short time window after a transaction begins.
Once an Ethereum account sends its first transaction, its public key becomes visible on the blockchain. After that, an attacker can keep working on the exposed key without racing against the clock. That creates what the paper called an at rest attack risk.
The researchers wrote,
“This results in account vulnerability: a systemic, unavoidable exposure that cannot be mitigated by user behavior, short of a protocol-wide transition to PQC.”
The paper also estimated that the 1,000 richest exposed Ethereum accounts, which hold about 20.5 million ETH, could be cracked in fewer than 9 days.
Post quantum cryptography moves into focus
The study said the crypto sector should prepare for post quantum cryptography before quantum attacks become possible. Google said it wants to raise awareness and help improve blockchain security and stability ahead of that point.
Last week, Google also set a 2029 deadline for its own post quantum cryptography migration. The company warned that quantum progress may be closer than many expect.
The report also drew reaction from Justin Drake, an Ethereum researcher and co author of the paper. He said,
“My confidence in Q-Day by 2032 has shot up significantly. IMO there’s at least a 10% chance that by 2032 a quantum computer recovers […] private key from an exposed public key.”
Meanwhile, the Ethereum Foundation released a post quantum roadmap in February, and Vitalik Buterin said validator signatures, accounts, proofs, and data storage must change to address future quantum computing risks.
Tatevik Avetisyan is an editor at Kriptoworld who covers emerging crypto trends, blockchain innovation, and altcoin developments. She is passionate about breaking down complex stories for a global audience and making digital finance more accessible.
📅 Published: March 31, 2026 • 🕓 Last updated: March 31, 2026
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