QUANTUM QNT

Exposed Public Keys and Address Reuse: Who Is Actually Vulnerable to Quantum?

Updated | 3 min read | QUANTUM (QNT) community

The key idea: the public key must be visible

Shor's algorithm, if run on a big enough error-corrected quantum computer, would let an attacker work backwards from a public key to the matching private key (see Shor's algorithm explained). No public key, no easy target. That is why the question is not "which coins are quantum vulnerable" in a yes or no sense, but "which coins have shown their public key, and for how long?"

Long exposure vs short exposure

BIP-360 draws a helpful line. Long exposure means a public key that sits on the chain for a long time, for example forever after an old output was created. Short exposure means the brief window between broadcasting a transaction and having it confirmed, when the key is visible only in the waiting room. A quantum attacker would have far more time with a long-exposed key. Defending against short exposure needs full post-quantum signatures. Defending against long exposure can be done by simply never publishing the key until spend time.

Where keys get exposed

The reported scale

BIP-361 states that over 34% of all bitcoin had revealed a public key on-chain as of March 1, 2026. Other analysts use narrower definitions, such as only coins that are both exposed and realistically at near-term risk, and get far smaller numbers, which shows how much the answer depends on definitions. Ethereum.org says the Ethereum Foundation estimates quantum-vulnerable dormant fund exposure at about 0.1%, and it frames what to do with dormant wallets as an open governance question with no community consensus.

Why this is good news in disguise

Because the weakness is about exposure, a lot of it is fixable by habit and design rather than waiting for a protocol miracle. Fresh addresses for every receive, wallets that do this automatically, and new output types that never reveal a key until needed all shrink the target. Sui reports that Google Quantum AI estimated in March 2026 that recovering a private key from an exposed public key could take minutes on a fault-tolerant machine with under half a million physical qubits, which is a useful reminder to close the exposure window early. Note that this is a research estimate and the machines do not exist today.

Practical takeaways

Never reuse receive addresses. Prefer wallets that rotate them. Treat very old wallets with exposed keys as the first ones to migrate when quantum-safe options exist. More in what individuals can do today and the protocol view in BIP-360 and BIP-361. For the Solana angle see will quantum computers break Bitcoin and Solana.

Education only, not financial advice. This page makes no prediction about any asset, and the QNT memecoin has no connection to Quantinuum Ltd.

Sources and further reading

Reported as of 2026-10-09. Roadmaps and proposals change often, so check the primary documents. Nothing here is financial advice. The QNT memecoin is independent of Quantinuum Ltd, the real company, and of every lab, chain and government named on this page.

Frequently asked questions

Why does address reuse matter for quantum risk?

Spending from an address reveals its public key. Any coins later received at the same address then sit behind a key that is already public.

Are all bitcoin vulnerable?

No. Coins whose public key has never been revealed are better protected. BIP-361 reports that over 34% of bitcoin had revealed a public key as of March 1, 2026.

Is my Ethereum account exposed?

If it has sent a transaction, its public key is on the chain. Ethereum.org says accounts that never sent one have an extra layer of protection.

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