Bitcoin developer Cory Fields has proposed making future quantum thieves put their own Bitcoin at risk before they can take someone else’s. The catch: legitimate owners moving vulnerable coins could face the same collateral requirement.
In a November 4 post to the Bitcoin development mailing list, Fields outlined “quantum landmines” and two auction mechanisms intended to make quantum-enabled theft an expensive gamble. He described them as thought experiments, not a finished Bitcoin upgrade.
As reported by Decrypt on November 8, 2026, none of these protections existed in Bitcoin, and Fields had published neither an implementation nor an activation schedule.
The threat is hypothetical, not a demonstrated attack
Bitcoin transactions rely on private keys to authorize spending and matching public keys to verify signatures. Today’s computers cannot realistically derive the private key from its public counterpart. A sufficiently powerful quantum computer could potentially do so using Shor’s algorithm, allowing an attacker to spend coins as though they were the owner.
Exposure varies. Some older Bitcoin outputs already expose public keys, as do certain newer formats. Other addresses conceal the public key until spending occurs.
Researchers call the hypothetical arrival of a computer capable of these attacks “Q-Day.” At the time of the report, no publicly demonstrated machine could steal Bitcoin this way, and the timing remained unknown.
A hidden ownership receipt—and a collateral bill
Fields’s landmine concept starts before Q-Day. An owner creates a small, separate quantum-safe Bitcoin output containing a hidden proof that they controlled an older wallet’s private key before quantum theft became possible. Outsiders could see the small output, but not the concealed evidence or whether it was a trap.
In the source’s example, an owner has 1 BTC in a potentially vulnerable wallet. Under the proposed rules, a future attacker who recovers its private key would have to contribute another 1 BTC from a quantum-safe wallet as collateral to move it.
The combined 2 BTC would enter a restricted output, subject to a challenge period—30 days in Fields’s example. If the owner notices and reveals the earlier proof in time, they could move both coins to the quantum-safe address committed to beforehand. The thief would lose their collateral.
That uncertainty is the deterrent: attackers would not know which wallets had hidden landmines.
But the rule would also apply to an honest owner making a normal post-Q-Day transfer of their legacy coin. Someone without spare Bitcoin could struggle to move their own savings. The mechanism does not magically distinguish a thief from an owner; it changes the cost of presenting the same valid signature.
Auctions for coins without an active defender
Landmines require an owner to prepare before Q-Day and respond during the challenge period. They cannot protect coins whose keys are already lost, including some early Bitcoin holdings widely believed to be inaccessible.
Fields outlined two other mechanisms:
- Staked auction: Before Q-Day, a participant would lock quantum-safe Bitcoin and secretly register a bid against a particular old wallet. In an example involving an apparently abandoned wallet holding 50 BTC, an attacker would post another 50 BTC as collateral to attempt a transfer. A bidder who committed in advance could challenge it. In Fields’s example, a successful challenger receives part of the attacker’s collateral, while the original vulnerable coins are destroyed—not returned to a missing owner or awarded to the bidder.
- Sats auction: No advance stake would be required. A vulnerable-coin spend would trigger a contest in which the highest bidder receives the coins minus their bid, while the runner-up pays their bid and receives nothing. The possibility of costly bidding escalation is meant to discourage an attacker from starting the contest.
These are deterrence proposals, not straightforward recovery tools. Fields’s original post left auction payouts and even the desired auction outcome unresolved.
The alternative to freezing coins has its own risks
Another proposed response to quantum risk is to restrict spending from outdated wallets after a migration deadline. That could prevent theft, but also permanently exclude legitimate owners who failed to move their coins.
Fields is exploring a different bargain: leave old coins potentially spendable, while making transfers costly and challengeable. The consequences could still be severe. Honest holders might need substantial collateral, inactive owners could miss their opportunity to object, and auctions might destroy coins belonging to people who are simply offline rather than absent forever.
Implementation would require a quantum-safe way to hold and spend Bitcoin, wallet support for hidden ownership commitments, and consensus rules covering collateral, waiting periods, recovery transactions and auctions. Developers would also need agreement on activation, collateral amounts, losing bids and leftover funds.
Fields believes some mechanics could be introduced through a soft fork, but had not supplied a detailed design. The proposal’s central claim is therefore still an open engineering and incentive question: can making quantum theft a gamble deter attackers without making legitimate ownership prohibitively expensive?
Original source: Decrypt, published November 8, 2026, at 22:01:03 UTC+08:00.