Research Identifies 6.9 Million Bitcoin Vulnerable to Future Quantum Attacks

A research paper from Google Quantum AI found that approximately 6.9 million Bitcoin reside in wallet addresses where the full public key is publicly accessible on-chain. This visibility exposes funds to an "at-rest" attack, in which a sufficiently advanced quantum computer could take unlimited time to calculate the corresponding private key offline. The study also identified roughly 20.5 million Ethereum tokens in similarly exposed states, representing about a sixth of Ether's circulating supply.

The vulnerability stems largely from address architecture and usage patterns. Early pay-to-public-key (P2PK) addresses publish the key immediately upon receiving funds, whereas pay-to-public-key-hash (P2PKH) addresses only disclose the key once a spending transaction is broadcast. Consequently, address reuse in P2PKH formats accounts for the majority of the vulnerable Bitcoin supply. Formats such as P2WPKH, P2SH, and P2WSH retain protection until spent, while Taproot outputs display public keys on-chain from inception.

Addressing the risk is complicated by dormant supply. Coinbase's Independent Advisory Board on Quantum estimates that about 1.7 million Bitcoin, worth roughly $131 billion at a $77,400 price level, are locked across approximately 20,000 early P2PK addresses dating back to the Satoshi era or otherwise considered lost, making migration to quantum-resistant standards impossible for those specific coins.