Researchers Halve Quantum Resource Estimate for Bitcoin, Ethereum Attack

Bitcoin uses a proof-of-work mechanism, and an attacker controlling more than 50% of the network’s computing power could theoretically reorganize its transaction history. An academic research team found that while quantum computing could accelerate calculations, a 51% attack on Bitcoin mining would still face physical constraints including hardware scale, cooling and energy supply, limiting the near-term threat.

As of July 20, 2026, the latest research estimates that a quantum computer powerful enough to overwhelm the entire Bitcoin network could require energy on the scale of a star, putting such a system beyond what existing institutions could deploy with funding alone. A more practical risk is the compromise of older wallets whose public keys remain exposed. Bitcoin developers have begun exploring quantum-resistant signatures and network upgrades.

Bitcoin and Ethereum rely on elliptic-curve cryptography to safeguard assets. A quantum computer capable of deriving a private key from a public key could potentially steal funds. Bitcoin activated Taproot on November 14, 2021, and because some transactions expose public keys in advance, the potential window for attack has widened.

The latest research from Google Quantum AI estimates that about 500,000 error-corrected physical qubits could be enough to crack a key within Bitcoin’s roughly nine-minute transaction confirmation window, far below previous estimates of several million qubits. No funds have been reported stolen through such an attack, but the researchers are urging the community to begin planning a migration to post-quantum cryptography.