Cats have a specific reaction to a threat they cannot evaluate. Not fear — something more like suspended judgement. Tuga will sit at a distance from a new object, absolutely still, for as long as it takes, and she will neither flee nor approach until she has decided what it is.

That is roughly the correct posture for quantum computing, and it is almost nobody's. The two popular positions are "bitcoin is doomed" and "it's nothing, stop worrying", and both are the work of people who would rather have a conclusion than a model.

Here's the actual shape of it.

1. Two Different Algorithms, Two Different Problems

Quantum computing threatens cryptography through two known algorithms, and they do very different amounts of damage.

Grover's algorithm speeds up brute-force search — relevant to hashing, and therefore to mining and to SHA-256. The speedup is quadratic, which sounds dramatic and isn't: it effectively halves the security in bits. SHA-256 drops to roughly 128-bit effective security, which remains comfortably beyond anything physically plausible. Mining and the hash functions are basically fine.

Shor's algorithm is the real one. It breaks the mathematics underneath elliptic-curve signatures — the system that proves you own your coins. With a sufficiently large, stable quantum computer, Shor's algorithm could derive a private key from a public key.

That's the threat. Not the chain, not the mining, not the hashes. The signatures.

2. When Is Your Public Key Actually Exposed?

This is the part that decides how bad it would be, and it's more nuanced than most articles admit.

A bitcoin address is a hash of a public key, not the key itself. So for most address types, the public key stays hidden until you spend from that address — at which point it's published on the chain forever.

The consequences:

• Coins at an address you've never spent from are, for now, protected by the hash. Shor's doesn't help against a hash.
• Coins at a reused address are exposed. The public key went public the first time you spent. This is one more reason for the address hygiene I wrote about earlier.
• Early coins in the P2PK format — including a large quantity from the very first years — have their public keys sitting in the open right now. Those are the most exposed, and many of them belong to people who are gone.
• Taproot outputs (bc1p) contain a public key directly. This is worth saying plainly, because it cuts against the usual advice: not reusing addresses does not fully protect a Taproot output the way it protects an older one. It's a real trade-off that was made knowingly, for good reasons, when the exposure was judged distant.

There's also a narrow live-transaction window: between broadcasting a spend and it confirming, your public key is public and the coins aren't yet moved. An attacker fast enough could theoretically race you. That requires a quantum computer far beyond anything demonstrated, operating in minutes.

3. How Far Away Is It?

Nobody knows, and anyone who gives you a date is guessing with confidence.

What can be said: breaking the curve bitcoin uses would require a machine with millions of stable, error-corrected qubits. Current devices are orders of magnitude short of that — the published qubit counts you see in headlines are noisy physical qubits, and the conversion to usable logical qubits is brutal. Estimates in the literature range from "a decade or two" to "possibly never at this scale", and the honest summary is that the uncertainty is enormous in both directions.

What is certain is that it wouldn't be a surprise. Building such a machine is a visible, expensive, years-long industrial effort. There would be warning.

4. What Would Happen If It Got Close

Bitcoin is not defenceless, and this is the part the doom version omits.

Post-quantum signature schemes already exist and are being standardised. Adding one to bitcoin is a soft fork — technically the same kind of upgrade as SegWit or Taproot. People would move their coins to quantum-resistant addresses. Uncomfortable, coordinated, slow, and entirely possible.

The genuinely hard problem isn't technical. It's the coins nobody can move: early P2PK holdings whose owners are dead or lost. Those would be sitting exposed while everyone else migrated, and the community would face a question with no comfortable answer — let them be taken, or freeze them, which means changing the rules about someone else's property. That argument will be uglier than the technical work.

5. The Missing Context

One last thing that gets left out of every panicked thread.

A quantum computer capable of breaking bitcoin breaks nearly everything else first. The same elliptic-curve mathematics secures HTTPS, banking, government communications, and the infrastructure of the internet. Bitcoin would not be the crisis; it would be a line item in a civilisational one — and unlike most of that infrastructure, bitcoin has an active community that has been discussing the migration for years.

If you want to worry about quantum computing, worry about it properly and broadly. Singling out bitcoin is a rhetorical move, not an analysis.

The Point

Tuga's response to the unfamiliar object is the right one: don't flee, don't approach, keep watching, decide when there's something to decide.

Quantum computing is a real long-term consideration and not a present emergency. The sensible response is boring: don't reuse addresses, keep your coins in formats you can migrate, and pay attention when the standards bodies start moving — not when a headline announces a new qubit record that means nothing on its own.

Sit at a distance and keep watching. That's not complacency, it's the correct amount of alarm. 🐾⚡