@Eli5DeFi: The threat isn’t quantum mining. It’s quantum signatures.

If you’ve ever said “quantum is decades away,” today’s news should make you pause. Google just published a paper suggesting a quantum computer could crack a Bitcoin private key in ~9 minutes, potentially moving the quantum timeline up to 2029. The thing is: that machine doesn’t exist yet. But the distance between “theoretical” and “practical” just shrank fast, and a lot of wallet hygiene that feels fine today is dangerously wrong for where this is going. The threat isn’t quantum mining. It’s quantum signatures. Bitcoin’s Proof-of-Work is fine. SHA-256 is fine. The soft spot is ECDSA, the signature scheme that proves you own your coins. Shor’s algorithm doesn’t brute-force keys. It solves the underlying math. Three realistic attack paths: 1) On-spend Watch a transaction in the public mempool, derive the private key, then front-run it with a forged transaction and a higher fee before confirmation. Some estimates put success around ~41% under current assumptions. 2) At-rest Target dormant wallets where the public key is already exposed. No time pressure. Works with weaker quantum hardware. 3) On-setup Crack setup parameters once, then turn it into a permanent classical exploit. Think Tornado Cash–style setups, and even Ethereum’s KZG data availability layer. Who’s exposed right now: - ~6.9M BTC may already be vulnerable across script types - Any address you’ve spent from has its public key permanently on-chain - Taproot (bc1p) exposes your public key the moment you receive funds And the part that changes the timeline: - Older estimates: ~9M physical qubits to break Bitcoin - Google’s newer circuits: under ~500K (about a 20x reduction) So yes, the computer isn’t here yet. But this is looking less like a physics problem and more like an engineering schedule. What to do now: - Stop reusing addresses - Avoid bc1p for cold storage if you’re optimizing for long-term quantum risk - Audit which wallets have already exposed public keys --- Eli5 Interactive research here: https://claude.ai/public/artifacts/ff56f…