On May 20, blockchain analytics firm Glassnode released a comprehensive report revealing that approximately 4.12 million BTC—roughly 20.6% of Bitcoin’s total supply—is vulnerable to future quantum computing attacks. The exposure stems not from a flaw in Bitcoin’s core protocol, but from widespread user behavior and poor key management practices.
Glassnode broke the vulnerability into two categories. Structural exposure, totaling 1.92 million BTC (9.6% of supply), arises from legacy transaction types such as Satoshi-era Pay-to-Public-Key outputs, legacy multisig structures, and Pay-to-Taproot outputs that inherently reveal public keys on-chain. Satoshi Nakamoto’s own coins account for roughly 1.1 million BTC of this risk. Operational exposure, the larger share at 4.12 million BTC, results from address reuse and partial spending habits that unnecessarily expose public keys. Exchange-held Bitcoin is disproportionately affected: about 1.66 million BTC (8.3% of supply) on exchanges falls into the exposed category, with Binance showing 85% exposed balances and Coinbase just 5%.
The report emphasizes that Bitcoin’s cryptography remains secure against classical computers, and there is no immediate quantum threat. However, future fault-tolerant quantum computers—estimated to require about 2,330 logical qubits to break elliptic curve cryptography—could theoretically derive private keys from exposed public keys. To mitigate the risk, Glassnode urged exchanges and custodians to reduce key reuse, improve address hygiene, and plan migration to quantum-proof formats. Proposed solutions like BIP-360 would offer a voluntary migration path using quantum-resistant Pay-to-Merkle-Root outputs. The full analysis underscores that while the protocol is sound, user education and better wallet design are critical to limiting long-term liabilities.
