The Truth About Quantum Computing & Bitcoin | Brandon Black

— Quantum computers exploit superposition of qubits to solve cryptographic problems exponentially faster than classical computers, but scaling from theoretical to practically useful devices remains the fundamental bottleneck.

— The highest number factored by quantum computers to date is 21 (achieved in 2012); a 6-bit elliptic curve key was recently solved, showing minimal real-world progress despite billions in investment.

— Bitcoin's vulnerability depends on attack speed: public keys exposed on-chain (pay-to-pubkey addresses, ~2M coins) are at risk immediately; others remain safe as long as quantum attacks take longer than ~10 minutes per block.

— Post-quantum cryptography solutions exist (hash-based, lattice-based) but require multi-kilobyte keys and signatures compared to Bitcoin's current 100-byte total, creating severe blockchain throughput trade-offs.

— A soft fork using BIP360 (quantum-resistant taproot variant) could be the next Bitcoin upgrade, solving multiple problems simultaneously and potentially shifting narratives away from ossification concerns.

— Focus on address security discipline: use segwit addresses and never expose public keys or extended public keys; pay-to-pubkey addresses should be considered permanently at risk if quantum threats materialize.

— A credible quantum threat requires concrete evidence of sub-exponential scaling in breaking elliptic curve keys—watch for demonstrations progressing from 6-bit to 10-bit to larger key reversals before treating the threat as imminent.

— Begin gradually migrating legacy Bitcoin holdings to quantum-resistant addresses *only after* a post-quantum soft fork activates; current speculation should not trigger panic selling or address migration.