Google has set a concrete deadline to migrate its infrastructure to post-quantum cryptography by 2029, signaling that the threat from quantum computing is no longer a distant theoretical problem. The company framed the move as urgent, arguing that quantum systems could eventually threaten the encryption and digital signature standards that underpin modern computing and, crucially, blockchain networks.
In a related development, Google's Quantum AI team published a whitepaper suggesting that breaking Bitcoin's cryptography may be easier than previously thought. The research indicates that a practical attack could require fewer than 500,000 physical quantum bits (qubits), a figure well below the millions often cited. More specifically, the team designed attack methods requiring roughly 1,200 to 1,450 high-quality qubits.
The proposed attack vector targets transactions in real-time. When a Bitcoin transaction is broadcast, the public key is briefly revealed. A sufficiently fast quantum computer could theoretically use this information to calculate the corresponding private key and redirect the funds. Google's model suggests such an attack could be prepared in advance and executed in about nine minutes, posing a threat given Bitcoin's average 10-minute block confirmation time.
The research also highlights that approximately 6.9 million bitcoin (about one-third of the total supply) are held in wallets where the public key has already been exposed, making them potentially vulnerable in a future quantum scenario. This includes around 1.7 million bitcoin from the network's early years.
Furthermore, the 2021 Taproot upgrade is noted as a complicating factor. While improving privacy and efficiency, Taproot made public keys visible on the blockchain by default, potentially expanding the pool of wallets vulnerable to quantum attacks by removing a layer of protection used in older address formats.
Google's shift from theoretical warnings to a defined corporate timeline, coupled with new research suggesting a lower technical barrier to attack, sharpens the focus on the long-term cryptographic transition facing decentralized networks like Bitcoin. The key challenge highlighted is not an immediate breach but the immense coordination required for a post-quantum upgrade across Bitcoin's global ecosystem of developers, miners, wallets, and users.
