Bitcoin dev Cory Fields proposes quantum landmines

Bitcoin Core developer Cory Fields has proposed a mechanism that would force anyone trying to steal coins with a quantum computer to put up their own Bitcoin first. Fields, who works at MIT’s Digital Currency Initiative, posted the idea to the bitcoin-dev mailing list on Wednesday, November 4, 2026, calling it “quantum landmines” and describing it as a thought experiment, according to Crypto Briefing.

The scheme targets a long-standing worry: Bitcoin’s public-key cryptography could, in theory, be reversed by a sufficiently powerful quantum machine, exposing the private key behind any public key already visible onchain. Rather than only racing to migrate to quantum-safe cryptography, Fields wants to change what an attack costs. Crypto Briefing reported the proposal on November 5, 2026.

Key facts

• Fields published the proposal to the bitcoin-dev mailing list on November 4, 2026, and labelled it a thought experiment rather than a specification.
• Under the design, anyone spending coins from a vulnerable address must post collateral from a quantum-safe wallet equal to the amount being moved.
• About 7.1 million BTC, roughly 35% of circulating supply, sat in wallets with exposed public keys as of early November 2026, per Crypto Briefing.
• crypto.news reported that Fields’ example involves a 30-day waiting period during which a legitimate owner could reveal a previously hidden ownership commitment and claim the attacker’s collateral.
• crypto.news also reported that Fields discussed an auction design, raised with MIT Digital Currency Initiative director Neha Narula, in which competing bidders could face financial penalties.

How the landmine works

The mechanism borrows from commit/reveal setups, which function like a sealed-bid auction: a participant locks in a commitment without showing it, then discloses the details later, so nobody can copy or front-run the move.

The landmine itself would be a small output in a quantum-safe format designed to reward or penalise whoever interacts with it. An attacker would need skin in the game. Act in good faith and the collateral returns; get caught attempting theft and it can be forfeited.

As crypto.news described it, someone moving 1 BTC from a vulnerable address would need another 1 BTC held in a quantum-safe wallet, with both amounts entering a new output carrying spending restrictions and a possible 30-day delay. An owner who had prepared a hidden commitment in advance could reveal it during that window and take back the coins plus the attacker’s stake. Because an attacker cannot know in advance whether such a commitment exists, the uncertainty is meant to deter attempts.

Fields acknowledged in the thread that Bitcoin cannot automatically tell a legitimate owner from an attacker who has recovered the same private key, and that he had not specified the software changes needed to implement the mechanism.

Auctions for wallets whose owners are gone

The collateral rule presumes the rightful owner still holds the private key and prepared a commitment before quantum attacks became practical. Many old wallets do not meet that condition, since keys have been lost and coins left untouched for years.

For those, Fields outlined bidders placing hidden bids against dormant holdings in advance. If an attacker later tried to spend the coins, an auction would open once the ownership-proof window closed, and bidders could reveal their earlier bids to claim part of the attacker’s collateral. Under the described mechanism, the vulnerable coins would be destroyed if an eligible bid stopped the attacker from keeping them. Fields weighed different ways to distribute collateral, including to successful bidders, miners or other designated recipients.

Neither auction design guarantees an original owner gets their coins back. The point is to make theft less attractive by putting the attacker’s own funds at risk.

Why it matters

The proposal sidesteps part of an argument that has split developer discussion: earlier ideas relied on voluntary migration to quantum-safe wallets, which respects property rights but depends on owners showing up, while soft-fork ideas that restrict at-risk UTXOs raise questions about who decides the fate of someone else’s Bitcoin. Fields’ alternative neither freezes nor seizes coins; it prices the attack.

For ordinary holders, the collateral requirement cuts both ways. Someone whose entire balance sits in an older-format wallet would need additional Bitcoin in a quantum-safe output to move their own funds under these rules.

The idea also depends on infrastructure nobody has built. Quantum-safe wallets would need to be standardised and adopted before any landmine could be planted, which makes this a complement to migration work rather than a substitute. Any version would need a soft fork, inheriting the consensus-building friction that entails. Fields said those mechanics remain unresolved.

What to watch

The immediate test is the bitcoin-dev thread itself. Crypto Briefing noted that no responses had appeared at the time of its report, so whether other developers poke holes or propose refinements will decide if the thought experiment moves toward a specification. The 7.1 million BTC figure with exposed public keys is the number to track as migration efforts and rival proposals progress. Separately, Coinbase urged developers in October to prepare for quantum threats, warning that migrating existing wallets could take several years, while a BitMEX proposal suggested restricting older wallets only after evidence of a successful quantum attack.

Disclaimer: This article is for information only and is not investment, financial or trading advice. Cryptocurrency prices are highly volatile. Always do your own research.

Sources: Crypto Briefing, crypto.news