Over 30% of Bitcoin Public Keys Exposed, Vulnerable to Quantum Computers

In brief

More than 30% of all Bitcoin already has its public key exposed on-chain, making it theoretically vulnerable to a future quantum computer attack.

The exposure breaks into two types: structural from script designs that reveal keys by default, and operational from address-reuse behavior.

Exchanges account for roughly 40% of operationally exposed Bitcoin, though the risk varies widely by platform and can be reduced through better wallet hygiene.

Nearly one-third of all Bitcoin in circulation—over 6 million coins worth over $469 billion as of this writing—is already vulnerable to theft if powerful quantum computers become a reality, according to research published Wednesday by blockchain analytics firm Glassnode.

The analysis, which examines the Bitcoin blockchain to determine which coins have already had their public cryptographic keys exposed, found that 6.04 million BTC, or 30.2% of the issued supply, is exposed to quantum risk, while the remaining 13.99 million BTC shows no public-key exposure. The estimate of exposed coins is lower than some existing figures, which have ranged closer to 7 million BTC.

The concern stems from the architecture underlying Bitcoin's security. Each coin is controlled by a private key, matched to a public key visible on the blockchain only under certain conditions. The quantum concern is that a sufficiently capable quantum computer, using an algorithm known as Shor's algorithm, could in principle recover a private key from a known public key.

In that scenario, any coin whose public key has already been revealed on-chain would be immediately targetable—no transaction required.

Glassnode separates the exposed supply into two distinct categories. Structural exposure accounts for 1.92 million BTC, or 9.6% of the issued supply. These are coins locked in script formats that reveal the public key by design, including early "pay-to-public-key" outputs associated with Bitcoin's pseudonymous founder Satoshi Nakamoto, legacy multisignature structures, and more recent Taproot outputs.

Many of these coins may be effectively immovable—lost wallets or dormant holdings that cannot be voluntarily migrated to safer address formats.

The larger and more actionable category is what Glassnode calls operational exposure. Operational exposure totals 4.12 million BTC, or 20.6% of the issued supply. These coins were not inherently vulnerable, but became so through address reuse—a practice where a wallet receives multiple transactions at the same address, eventually broadcasting the public key during a spend and leaving any remaining balance exposed.

Exchanges loom large in this category. Within the operationally unsafe bucket, 1.66 million BTC, or 8.3% of the total supply, is exchange-related—representing approximately 40% of all operationally unsafe Bitcoin. The exposure is strikingly uneven across platforms. Among the largest exchanges, Coinbase's labeled balances appear largely concentrated in non-exposed structures, with only 5%exposed, while Binance and Bitfinex show comparatively high susceptible balances—85% and 100%, respectively.

Glassnode was careful to note that its findings should not be read as a risk ranking or solvency signal for any particular firm, stressing that the data reflects custody design choices rather than imminent danger. Sovereign Bitcoin holdings fared considerably better: the United States, United Kingdom, and El Salvador all show zero quantum exposure.

The report stops well short of predicting when—or whether—a quantum computer capable of cracking Bitcoin's encryption will exist. It frames its analysis instead as a baseline, noting that for exchanges and custodians, address hygiene, reserve management, reduced key reuse, and migration planning are the practical levers through which visible exposure can decline.

The findings arrive as quantum computing advances accelerate globally and as the Bitcoin developer community debates protocol-level responses, including a proposed update known as BIP-360 that would introduce more quantum-resistant transaction formats. Another official proposal would freeze coins that are not migrated by a set deadline.