Google: Quantum Computers Could Threaten Bitcoin Sooner Than Expected
Breaking Bitcoin’s blockchain with quantum computers may be easier than previously thought, and the Taproot upgrade — designed to improve privacy and efficiency — could be partly responsible, according to Google’s Quantum AI team. In a blog post and newly released whitepaper, researchers said the computing power required to compromise Bitcoin’s cryptography is likely far lower than earlier estimates.
The study found that fewer than 500,000 physical qubits could be enough to break the encryption behind Bitcoin and Ethereum, a sharp drop from the “millions” cited in previous research. Google had previously indicated 2029 as a key milestone for practical quantum systems, emphasizing that crypto migration to quantum-resistant protocols should happen before then. These findings suggest the timeline for quantum threats may be shorter than anticipated.
Quantum computers, which use qubits instead of traditional bits, can solve complex problems much faster, including cracking crypto wallet encryption. Google modeled two potential attack methods, each requiring roughly 1,200–1,450 high-quality qubits — far below prior estimates — suggesting that a practical attack could be closer than expected.
Rather than targeting dormant wallets, a quantum attacker could exploit live transactions. When bitcoin is sent, a public key is briefly exposed. A fast quantum computer could calculate the private key and redirect the funds. Google estimates that such an attack could be executed in about nine minutes, slightly shorter than the typical 10-minute confirmation window, giving attackers around a 41% chance of intercepting a transaction. Cryptos with faster confirmation times, like Ethereum, would be less exposed to this risk.
The whitepaper also notes that about 6.9 million BTC — roughly one-third of the total supply — already sit in wallets where the public key has been revealed, including 1.7 million BTC from Bitcoin’s early years. This is far higher than previous estimates of concentrated risk, such as CoinShares’ 10,200 BTC figure.
Taproot, Bitcoin’s 2021 upgrade, plays a key role in the risk. While it improved privacy and transaction efficiency, Taproot makes public keys visible on the blockchain by default, removing a layer of protection present in older addresses and increasing the number of wallets potentially vulnerable to quantum attacks.
To avoid exposing attack methods, Google shared its research using zero-knowledge proofs, allowing verification without giving step-by-step instructions for exploitation.
The takeaway for investors: quantum computers aren’t an immediate threat to crypto, but the potential timeline for attacks may be shorter and the risks broader than previously assumed.
