New research from Google suggests that breaking the cryptographic security of Bitcoin may be easier—and potentially sooner—than previously believed, raising fresh concerns about quantum computing risks in crypto.
Traditionally, experts assumed it would take millions of quantum bits (qubits) to crack Bitcoin’s encryption. However, Google’s Quantum AI team now estimates that fewer than 500,000 qubits could be enough, with some attack scenarios requiring only around 1,200–1,450 high-quality qubits. This significantly lowers the technical barrier and suggests the timeline for a real threat may be shorter than expected, especially with projections pointing to meaningful quantum systems emerging before the end of the decade.
The research highlights a practical attack scenario: instead of targeting old wallets, attackers could exploit transactions in real time. When a Bitcoin transaction is broadcast, a public key is briefly exposed. A sufficiently advanced quantum computer could use that data to derive the private key and redirect funds before the transaction is confirmed. Since Bitcoin transactions typically take around 10 minutes, the study estimates attackers could have roughly a 41% chance of intercepting a transaction under optimal conditions.
The findings also raise concerns about Ethereum and other cryptocurrencies, although faster block times may reduce their exposure to this specific type of attack. Still, the broader implication is that many blockchain systems relying on similar cryptography could face future risks.
A key factor in Bitcoin’s vulnerability may be its Taproot upgrade. While Taproot improved efficiency and privacy, it also made public keys more visible on-chain by default, potentially increasing the number of wallets exposed to quantum attacks. According to the research, around 6.9 million BTC—roughly one-third of the total supply—may already be in wallets with exposed public keys, making them more vulnerable over time.