NIST racetrack ion trap developed as possible quantum computing hardware

Bitcoin Developer Proposes ‘Quantum Landmines’ to Make Future Attacks a Losing Bet

By Isaac • November 12, 2026 3:29 pm • Comments

A Bitcoin developer has proposed a deliberately adversarial way to deal with a future quantum attacker: make the thief put up enough Bitcoin that a failed attack becomes an expensive gift to the real owner.

Cory Fields calls the idea a “quantum landmine.” It is not finished Bitcoin code, and it is not a prediction that quantum computers can break Bitcoin today. Fields presented it as a thought experiment for a possible future migration after the network has a quantum-safe output type.

In a Nov. 4 post to the Bitcoin Development Mailing List, Fields assumed a future “Q-day” when sufficiently powerful quantum machines might recover private keys from vulnerable public keys. Under his proposal, spending an old output after that point would require matching collateral in a quantum-safe output.

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The thought experiment starts with a user who owns both a legacy coin and a quantum-safe coin. Before Q-day, the owner places a hidden proof of prior key knowledge inside a small quantum-safe output, creating a private claim that a later attacker cannot manufacture retroactively.

After Q-day, new consensus rules would force any legacy spend to include full collateral and place the combined value behind a delay. The legitimate owner could use the earlier proof during that window, while an attacker who learned the key only after quantum machines arrived could not.

The collateral would remain locked for a waiting period. A legitimate owner who had committed a hidden proof before Q-day could reveal that proof, move the vulnerable coins and seize the attacker’s collateral.

An attacker who derived the key later with a quantum computer would lack that earlier proof and would have to wait, giving the owner time to spring the landmine.

Decrypt highlighted the economic reversal at the heart of the proposal. A quantum attack would no longer be a clean race to steal exposed coins.

The attacker would have to risk an equal amount of sound collateral, while the legitimate owner could be rewarded for detecting and proving the theft attempt. That changes the calculation from “can this key be broken?” to “is stealing this coin worth risking the same amount?”

The proposal remains preliminary, and the reporting makes clear that it would require new Bitcoin rules plus widespread preparation before any quantum emergency. Its immediate value is as a concrete design that developers can test against edge cases while today’s machines still pose no such threat.

Fields also described vulnerable-coin auctions as another possible path. Instead of letting old coins become a winner-take-all prize for the first attacker, special rules could force vulnerable outputs into a structured process.

That could create a window for legitimate owners to prove prior control while reducing the incentive for a sudden mass theft.

The proposal treats quantum defense as an incentives problem as well as a cryptography problem. Bitcoin cannot make old signatures quantum-resistant after the fact.

It may, however, be able to change the rules around how vulnerable outputs are spent, raising the cost of theft and giving prepared owners an escape route.

The hard part is coordination. Fields explicitly left the soft-fork mechanics for later work.

Any rule affecting old coins would force Bitcoin developers and users to confront difficult questions about proof standards, waiting periods, dormant holdings and the line between protecting property and changing long-established spending rights.

Quantum risk is already part of the broader custody debate, even though the machines required to execute the feared attack do not exist today. The practical lesson is not to panic or hand coins to the first custodian using the word “quantum.” It is that migration planning needs to begin long before a cryptographic emergency.

Fields’ landmine idea gives developers a concrete mechanism to attack, refine or reject while there is still time. Bitcoin’s strongest defenses have historically come from public proposals receiving years of hostile review.

A plan that can survive that process would be far more useful than a rushed answer after Q-day arrives.

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