Bitcoin's 1.7 Million BTC in Legacy Outputs Face Future Quantum Risk

A June 2026 estimate identified about 1.7 million Bitcoin (BTC) in legacy pay-to-public-key outputs, highlighting the coins' exposure if a future quantum computer can derive private keys from public keys.

The estimate covered roughly 20,000 public keys. Pay-to-public-key, or P2PK, is an early Bitcoin output format that displays a public key on-chain before the coins move.

A private key creates the signature that authorizes a Bitcoin transfer, while a public key lets the network check it. A sufficiently powerful quantum computer could potentially derive a private key from a visible public key and use it to authorize a transfer. No quantum computer can carry out that attack today.

A broader March 1 snapshot counted 6.9 million BTC with public keys revealed on-chain. That figure includes outputs beyond the legacy P2PK group. The two estimates cover different groups and were made at different times; neither is a new October count.

Other Bitcoin output types can reveal a public key when coins are spent. If funds remain at or are later sent to the same revealed public-key hash, they would share the potential vulnerability. Revealing a key does not, by itself, mean those funds can be taken with current technology.

The security question extends beyond identifying exposed coins. Protecting them against a future attack would require a way to move funds to outputs that use quantum-resistant signatures. Owners would then have to make those transfers while they still control their private keys.

BitGo introduced wallet controls for exposed Bitcoin addresses in July. They include a risk score and a process for moving funds. The controls address how wallets handle exposure under Bitcoin's existing rules.

A separate proposal, Bitcoin Improvement Proposal 361, outlines a staged move away from signatures vulnerable to a future quantum attack. It remains a draft and has not become an active Bitcoin network rule.