Europol Warns Quantum Attacks Threaten 6 Million Exposed Bitcoin as Security Upgrades Risk Network Bloat

Europol's European Cybercrime Centre reports that cryptocurrency wallets are the primary point of exposure for quantum attacks, warning that private keys could be derived from exposed public keys by future fault-tolerant machines. Blockchain analytics firm Glassnode estimates that 6.04 million BTC, representing 30.2% of the issued supply, already has its public key exposed on-chain. Upgrading to NIST-standardized post-quantum signatures will bloat transaction sizes by 10 to 120 times compared to current ECDSA signatures, threatening to overload block space and inflate network fees. A cited 2024 study estimates that migrating every unspent transaction output to quantum-safe standards would require at least 76 days of cumulative downtime, or roughly 300 days if the migration consumed 25% of each block. A second report developed with Spain's University Carlos III of Madrid warns of "Harvest Now, Decrypt Later" attacks targeting widely used protocols like TLS, SSH, and OpenPGP to capture encrypted data for future decryption. "Cryptocurrencies will not collapse due to quantum computing." — Europol