A new defensive concept has emerged to prepare for bitcoin hacking using future quantum computers by requiring attackers to put up their own bitcoin as collateral. Even if a quantum computer extracts a private key from an old wallet, the plan would force additional collateral and a dispute process. It is designed so that even a successful hack results in losses for the attacker.

On Nov. 8, blockchain media outlet Decrypt reported that bitcoin developer Cory Fields recently proposed "Quantum Mines" and two auction methods on the Bitcoin developer mailing list. It is still a thought experiment rather than a complete design for deployment. The proposal is drawing attention as a new way to protect bitcoin wallets that could be vulnerable in the quantum-computing era.

The proposal stems from concern that quantum computers could neutralise existing cryptographic systems. With today’s conventional computers, deriving a private key from a public key is effectively impossible. If sufficiently powerful quantum computers emerge, they could reverse it using Shor's algorithm. Older bitcoin wallets whose public keys have already been exposed could face relatively greater risk.

The core of Fields' Quantum Mines proposal is to impose extra costs on attackers. Before "Q-day" - the point when quantum computers could threaten cryptographic systems - users pre-register private information in a quantum-safe wallet to prove they were the original bitcoin owner. It is designed so outsiders cannot determine whether such information exists.

If an attacker later reconstructs the private key of an existing wallet with a quantum computer and tries to move 1 BTC, the network would demand an additional 1 BTC as collateral. A total of 2 BTC would be locked under restrictions. In Fields' example, a 30-day dispute period is provided.

If the original owner reveals the proof registered in advance during that period, the network would transfer both the original 1 BTC and the attacker’s 1 BTC deposit, for a total of 2 BTC, to the owner’s quantum-safe address. The attacker would lose not only the attempt to steal bitcoin but also their own assets.

A key point is that attackers cannot know in advance which wallets have a quantum mine installed. Because they cannot be sure a hack will succeed while still needing to post additional collateral of the same amount, the plan is described as reducing the economic incentive to attack.

The approach also creates burdens for legitimate owners. After Q-day, users seeking to move bitcoin from an existing wallet may also need to secure collateral of the same amount. Users without extra bitcoin could face constraints even when trying to move their assets normally.

Fields also proposed auction methods targeting vulnerable wallets that have been left unattended for a long time or whose owners are difficult to identify. The first is a pre-deposit auction. Before Q-day, participants pre-deposit quantum-safe bitcoin and register bids against a specific vulnerable wallet.

For example, if an attacker targets a wallet holding 50 BTC and tries to move the coins by posting 50 BTC as collateral, a participant who bid in advance can dispute it. In that case, the challenger takes part of the attacker’s collateral. The coins in the original vulnerable wallet are not paid out to the winning bidder but are burned. The aim is to eliminate the profit that could be obtained through hacking.

The second is a "Sats" auction that does not require pre-deposits. When a movement of vulnerable coins occurs, an auction opens and the highest bidder takes the remaining coins excluding their bid amount. The runner-up pays their bid amount but receives nothing. The mechanism is designed to deter hacking attempts by making attackers bear costs larger than the profits they expected.

There are also many issues to resolve. Quantum mines work only if owners prepare in advance before Q-day, and they are difficult to apply to coins whose private keys have already been lost. If users who remain offline for long periods miss the dispute window, they could lose legitimate assets.

There are also fundamental technical limits. The bitcoin network cannot distinguish between a valid signature created by a legitimate owner and a signature from an attacker who reconstructed the private key with a quantum computer. To actually enforce collateral, disputes and auctions, Bitcoin’s consensus rules would need to be changed.

That would require quantum-safe wallets and transaction methods, as well as technical foundations to support hidden ownership proofs, collateral deposits, waiting periods and recovery transactions. Fields mentioned the possibility of introducing some functions via a soft fork, but did not present a specific implementation method or activation schedule.

No such protective measures are currently applied on the bitcoin network. The proposal itself is also closer to an early concept, with no implementation code or formal rollout plan. It is meaningful in that it raises the issue that, to prepare for the possibility that advances in quantum computing could threaten the safety of existing cryptographic systems, defences should block not only technically but also attackers’ economic gains.