Cory Fields Proposes Bitcoin “Quantum Landmines” to Deter Theft

A proposed deterrent for quantum-era theft

Bitcoin Core developer Cory Fields has proposed “quantum landmines,” a mechanism intended to make stealing vulnerable Bitcoin costly for an attacker. He introduced the idea to the Bitcoin Development Mailing List on November 4, as concern grows about a future point described as Q-Day, when powerful quantum computers could break Bitcoin’s current cryptography. The proposal is a suggested response, not a change already in effect.

The concept centers on a hidden proof of ownership prepared before quantum attacks become possible. The source’s example is an owner with 1 BTC in an older, vulnerable wallet who places a secret proof inside a small quantum-safe Bitcoin output. The proof is not publicly visible. Its purpose would be to let the owner later establish a claim if someone tried to move the vulnerable coins.

Under the proposed rules, moving vulnerable Bitcoin after quantum attacks become possible would require the spender to provide an equal amount as collateral. In the example, spending 1 vulnerable BTC would require another 1 BTC in collateral. Both amounts would then face a waiting period that could last 30 days, giving a genuine owner time to respond rather than allowing a transfer to settle immediately.

How the collateral mechanism would work

If a quantum attacker tried to take the coins, the owner could reveal the secret proof during the waiting period, recover the original Bitcoin and claim the attacker’s deposit. That outcome is the proposal’s deterrent: a theft attempt could leave the attacker poorer, while the owner might recover the coins and the matching collateral. Fields’ argument is that uncertainty about hidden protections could make would-be thieves wary of targeting coins.

The mechanism’s basic logic is to put a potential attacker’s funds at risk alongside the vulnerable coins they seek to move. A hidden proof would not prevent an attempted theft outright; instead, it would give an owner a way to contest it after the move begins. The collateral requirement and delay are therefore central to the idea, while the proof provides the basis for recovering the coins and seizing the deposit.

The proposal also depends on owners acting before Q-Day and preparing the proof in advance. If someone has not created a landmine, the described protection would not be available for those coins. The source does not specify how widespread preparation would be, how the rules would be implemented, or how the system would settle contested claims beyond the proof-and-waiting-period outline. Those details remain open in the account provided.

The burden on legitimate owners

The most direct drawback is that Bitcoin’s blockchain cannot tell a quantum hacker from a legitimate owner moving vulnerable coins. As a result, the same collateral requirement would apply to both. A holder seeking to move 10 BTC from an old wallet could need 10 BTC in quantum-safe funds as well. That would make access to existing savings depend on having an equal amount available as additional collateral.

This creates a tension between deterring theft and preserving practical access for honest owners. The rule might raise the cost of attacking vulnerable coins, but it would also apply even when the person moving them is their rightful owner. In particular, matching collateral could be a substantial barrier for holders who do not have extra quantum-safe Bitcoin on hand. The source identifies this burden, but does not offer a way to waive it for legitimate transfers.

A waiting period could give an owner time to reveal a proof, but the same process would still require the owner to have prepared that proof and be able to use it. The account does not explain how disputes would be resolved if claims conflicted, or what happens when an owner cannot respond within the window. Those unanswered questions matter because the proposal treats every move of vulnerable coins alike before a valid claim is established.

Dormant coins and unresolved choices

Dormant coins pose a distinct challenge. If private keys have been lost, their owners cannot prepare a landmine, so the proposed protection cannot simply be activated for those holdings. The source raises Satoshi-era coins as an example of the broader problem: coins that do not move may be exposed, yet there may be no reachable owner able to prove a claim or recover them if a quantum attacker acts.

Fields has suggested alternative auction mechanisms for cases where a key holder cannot prepare a landmine. In the versions described, bidders could challenge hackers and seek to claim their deposits. One possible design would permanently destroy the vulnerable coins. This shifts the question from protecting an identifiable owner to deciding what should happen when ownership cannot be demonstrated, and the source presents these mechanisms as proposals rather than settled policy.

Destroying vulnerable coins would also raise questions about ownership and Bitcoin’s supply, while leaving them untouched could leave some coins without a practical defense. The source describes no consensus on how to resolve that choice, nor on whether the collateral system or auction alternatives would be adopted. For now, the proposal highlights a trade-off: stronger defenses against future quantum theft could make older coins more difficult or costly for legitimate holders to move.

Source: BeInCrypto