- Google said Bitcoin may need fewer qubits to crack than prior industry estimates.
- Taproot may widen wallet exposure by making public keys visible on-chain by default.
- Real-time attacks could exploit Bitcoin’s confirmation window in about nine minutes.
Google’s Quantum AI team said Monday that breaking Bitcoin’s blockchain with quantum computers may require far less computing power than many recent estimates suggested. In a blog post and whitepaper, the team said fewer than 500,000 physical qubits could threaten Bitcoin and Ethereum cryptography. It also said Bitcoin’s Taproot upgrade may widen exposure because it reveals public keys by default.
Lower Qubit Estimates Reshape the Threat Timeline
Google’s researchers said recent discussions often placed the requirement in the millions of qubits. By contrast, the new paper said an attack may need fewer than 500,000 physical qubits. As a result, the gap between today’s systems and a practical attack appears smaller.
The team also described two possible attack methods. Each model would need about 1,200 to 1,450 high-quality qubits. That figure sits well below older estimates and may change how investors view the timeline.
Google has already pointed to 2029 as a possible milestone for useful quantum systems. Because of that timeline, the lower resource estimate adds weight to calls for earlier migration. In turn, the findings raise fresh questions about how soon quantum risk could move from theory to planning.
Real-time Attacks Could Target Live Transactions
The paper said a quantum attacker may not need to target dormant or older wallets. Instead, the attacker could watch for a live Bitcoin transaction and act when the public key appears. At that moment, a powerful quantum system could try to derive the private key.
Google said its model lets the attacker complete some work before a target transaction appears. Then, once the public key becomes visible, the system could finish the attack in about nine minutes. Bitcoin transactions usually take around 10 minutes to confirm.
That timing gives the attacker about a 41% chance of redirecting funds before the original transfer settles. What happens if that attack window becomes practical before the industry completes a migration? The paper said Ethereum and some other networks may face less risk from this exact method because they confirm transactions faster.
Exposed Keys and Taproot Add to The Risk
Google’s researchers estimated that about 6.9 million bitcoins already sit in wallets with exposed public keys. That total equals roughly one-third of the total supply. It includes about 1.7 million bitcoin from Bitcoin’s early years and more funds linked to address reuse.
That estimate stands far above a recent figure from CoinShares. CoinShares argued that only about 10,200 bitcoins sit in concentrations large enough to move markets if stolen. The difference shows how firms measure quantum exposure in very different ways.
Related: BTQ Technologies Deploys BIP 360 Testnet to Shield Bitcoin From Quantum Threats
The findings also turned attention toward Taproot, Bitcoin’s 2021 upgrade. Taproot improved efficiency and privacy, yet it also made public keys visible on-chain by default. Google’s team said that the design choice may expand the number of wallets exposed to future quantum attacks.
Google also said it is changing how it discloses sensitive security research. Rather than publish a full attack playbook, the team used a zero-knowledge proof to show that its results hold up without exposing the method. At the same time, governments and industry groups are pushing quantum-safe encryption, while CoinDCX has launched a ₹100 crore fund for customer education, cybercrime support, and digital threat research.
