Quantum Computing Threat Concentrated in Legacy Bitcoin Wallets

The perceived threat of quantum computing to the Bitcoin network is often framed as a total collapse, but technical analysis suggests a more nuanced, tiered risk model. The primary vulnerability lies not in the network's overall architecture, but in dormant addresses with exposed public keys, particularly those from the 'Satoshi era.' While modern Bitcoin addresses employ advanced security layers, legacy wallets remain structurally exposed. Because these coins are 'at-rest' and often belong to inactive or lost accounts, they cannot be migrated to quantum-resistant formats, leaving them open to long-term decryption attempts by future quantum machines. The risk centers on the distinction between hash functions and public-key cryptography. While SHA-256 mining is relatively resilient to Grover’s algorithm, public-key cryptography—specifically ECDSA and Schnorr—is susceptible to Shor’s algorithm. This would allow a powerful quantum computer to derive a private key from a known public key. Analysts distinguish between 'on-spend' attacks, which occur during a transaction window of roughly 10 minutes, and 'at-rest' attacks. The latter are far more dangerous for dormant wallets, as attackers have indefinite time to compute private keys without needing a transaction trigger. Ultimately, this structural vulnerability creates a high-value, low-resistance target profile for future quantum computers. However, because active users can migrate their funds to updated security standards, the risk is concentrated in a specific segment of the supply rather than the entire ecosystem.