Bitcoin’s Taproot upgrade may be easing the path for quantum attacks, Google researchers suggest.

Google: Quantum Computers Could Threaten Bitcoin Sooner Than Expected

Bitcoin’s blockchain may be more vulnerable to quantum computing than previously thought, and the Taproot upgrade — which enhances privacy and efficiency — could be partly responsible, according to Google’s Quantum AI team. In a blog post and newly published whitepaper, researchers suggest the computing power required to compromise Bitcoin’s cryptography is significantly lower than earlier estimates.

The study found that fewer than 500,000 physical qubits could potentially break Bitcoin and Ethereum’s encryption — far below the “millions” previously assumed. Google had flagged 2029 as a key milestone for practical quantum systems, meaning preparations to migrate crypto to quantum-resistant protocols may be needed sooner than expected.

Quantum computers use qubits instead of traditional bits, allowing them to solve complex problems much faster, including the encryption securing crypto wallets. Google modeled two potential attack methods, each requiring roughly 1,200–1,450 high-quality qubits, suggesting the gap between today’s technology and a viable attack may be smaller than many believe.

Rather than attacking dormant wallets, quantum attackers could target transactions in real time. Bitcoin’s public key is briefly exposed during a transaction. A fast quantum computer could use that information to calculate the private key and redirect the funds. Google estimates such an attack could succeed in roughly nine minutes, slightly shorter than the typical 10-minute confirmation time, giving attackers about a 41% chance of intercepting the transfer. Faster networks, like Ethereum, would be less exposed.

The report notes that about 6.9 million BTC — roughly a third of all Bitcoin — already sit in wallets where public keys have been exposed, including 1.7 million from the network’s early years. Taproot, Bitcoin’s 2021 upgrade, made public keys visible by default, increasing the number of wallets potentially vulnerable to quantum attacks.

To reduce risk, Google shared its findings using zero-knowledge proofs, allowing verification without revealing attack methods.

Investors should note that while quantum computers are not an immediate threat, the timeline for potential attacks may be shorter and the risks broader than previously assumed.

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