Cory Fields Proposes Quantum Landmines for Bitcoin Wallets

Cory Fields’s Nov. 4 proposal would require a quantum thief to post 1 BTC of quantum-safe collateral for every 1 BTC taken from a vulnerable Bitcoin wallet. The design would replace a direct theft with a matched, challengeable transaction, but none of these protections exists in Bitcoin today.

Fields, a Bitcoin developer, presented “quantum landmines” and two auction designs in a post to the Bitcoin development mailing list. He called the ideas “thought experiments,” not a completed upgrade, and has published no implementation or activation schedule.

How would a quantum attack work?

Bitcoin owners authorize transactions with a secret private key; a matching public key lets the network verify a signature. Present-day computers cannot realistically derive the private key from the public one, but a sufficiently powerful quantum computer could use Shor’s algorithm and spend exposed coins as their owner.

Researchers call the arrival of such a machine “Q-Day.” No publicly demonstrated computer can steal Bitcoin this way today, and no one knows when one might appear. Some older Bitcoin outputs expose public keys, while certain newer formats reveal them; other addresses keep the public key hidden until a spend.

What does a quantum landmine change?

Under Fields’s example, the owner of 1 BTC in an old, potentially vulnerable wallet creates a tiny, separate quantum-safe Bitcoin output before Q-Day. The output contains hidden proof that the owner controlled the original private key while quantum theft remained impossible.

Think of it as a sealed ownership receipt: outsiders can see the small output, but not the evidence inside or the trap. If a future thief recovers the old private key, the thief must add 1 BTC from a quantum-safe wallet.

Both coins enter a restricted output worth 2 BTC, which remains unspendable through a 30-day challenge period. After noticing the transaction, the owner reveals the pre-Q-Day proof, and the network permits the full 2 BTC to move to the quantum-safe address committed earlier.

The attacker cannot know in advance which legacy wallets contain the hidden receipt, turning key recovery into a possible 1 BTC loss. The owner also needs matching collateral to move a legacy coin normally after Q-Day; without spare BTC, the same requirement could impede access to savings.

How would the two auctions work?

Landmines require an owner to prepare before Q-Day and reveal the proof in time. They cannot protect coins whose keys were already lost, including some early Bitcoin holdings widely believed to be inaccessible.

Fields’s staked-auction design would let someone lock quantum-safe Bitcoin before Q-Day and secretly register a bid against a specific old wallet they expect a thief to target. In his 50 BTC example, the attacker moves the apparently abandoned wallet and posts another 50 BTC as collateral.

During the auction period, a bidder who registered in advance can challenge the theft and claim part of the attacker’s collateral. The original vulnerable coins would be destroyed rather than awarded to the bidder, depriving thieves of a reliable payday rather than returning the coins to a missing owner.

Fields’s sats auction requires no advance stake. A spend from a vulnerable wallet would trigger a contest: the highest bidder receives the coins minus the bid, while the runner-up pays its bid and receives nothing. Because the runner-up can lose its entire deposit, two bidders could keep raising offers, potentially making a contest more expensive than the coins a thief hoped to steal.

Why not freeze vulnerable Bitcoin?

One proposed response to quantum risk would restrict spending from outdated wallets after a migration deadline. That could prevent theft, but it could also permanently lock out legitimate owners who never moved their coins.

Fields instead considers leaving old coins spendable while making transfers costly and open to challenge. Bitcoin cannot distinguish an honest owner from a quantum thief when both present the same valid signature. The design still burdens honest owners with large collateral, risks excluding inactive holders who miss the objection window and can burn coins belonging to people who remain alive but offline.

What would implementation require?

Bitcoin first needs quantum-safe ways to hold and spend funds. Wallets would then need support for hidden ownership commitments, while consensus rules would enforce collateral, waiting periods, special recovery transactions and auctions.

Developers must also settle when any rules activate, how much collateral to require and how to handle losing bids or leftover funds. Fields believes some mechanics could enter through a soft fork, a type of Bitcoin rule change, but he supplied no detailed design, auction payout schedule or intended final outcome.

The next gating milestone is a complete specification and community agreement on activation. Until then, the proposed 30-day challenge window and both auction mechanisms remain outside Bitcoin’s spending rules.