For long-term Bitcoin holders, protecting an old wallet from a future quantum attack could come with a difficult trade-off: a rule that makes theft expensive might also make legitimate access harder.
In a November 4 post to the Bitcoin development mailing list, developer Cory Fields outlined “quantum landmines” and two auction mechanisms intended to make attacks on vulnerable coins risky. As Decrypt reported on November 8, 2026, these are thought experiments—not available wallet protections or a completed Bitcoin upgrade.
The risk depends on public-key exposure
Bitcoin owners authorize transactions with a secret private key. A corresponding public key lets the network verify signatures without learning that secret.
Today’s computers cannot realistically derive the private key from the public key. A sufficiently powerful quantum computer could potentially do so using Shor’s algorithm, allowing an attacker to spend someone else’s coins.
Exposure is not identical across wallets. Some older Bitcoin outputs expose public keys, as do certain newer formats. Other addresses conceal the public key until coins are spent.
Researchers call the hypothetical arrival of a computer capable of such attacks “Q-Day.” At the time of the report, no publicly demonstrated machine could steal Bitcoin this way, and its arrival date was unknown.
A hidden ownership receipt—and a matching deposit
Fields’s landmine proposal would let an owner prepare evidence of ownership before Q-Day. In the article’s example, someone holding 1 BTC in an older, potentially vulnerable wallet creates a small, separate quantum-safe output containing a hidden proof that they controlled the original private key before quantum theft became possible.
Outsiders could see that small output, but not the evidence inside it—or identify it as a trap.
Under the proposed rules, a future attacker who recovered the old private key would have to contribute 1 BTC of their own from a quantum-safe wallet to move the vulnerable 1 BTC. Both coins would enter a restricted output worth 2 BTC, subject to a challenge period—30 days in Fields’s example.
If the owner noticed the transaction and revealed the earlier proof in time, they could move the full 2 BTC to the quantum-safe address they had previously committed to. The attacker would lose their collateral, without being able to tell beforehand which wallets had hidden proofs.
The access problem is that an honest owner would also need matching collateral to initiate a normal post-Q-Day transfer of their own legacy coin. Someone without spare BTC could struggle to move their savings. Protection would also depend on preparing the proof before Q-Day and responding within the challenge period.
Auctions for coins without a prepared owner
Landmines would not protect coins whose private keys were already lost. Fields proposed two other mechanisms to make targeting vulnerable holdings less attractive.
Staked auction
Before Q-Day, a participant could lock up quantum-safe Bitcoin and secretly register a bid against a particular old wallet.
In the example of an apparently abandoned wallet holding 50 BTC, an attacker would post another 50 BTC as collateral to attempt a transfer. A participant who had committed a bid in advance could challenge that attempt during the auction period.
In Fields’s example, a successful challenger would receive part of the attacker’s collateral, while the original vulnerable coins would be destroyed. The mechanism is intended to deny thieves a dependable payout, not recover funds for a missing owner.
Sats auction
This version would require no advance stake. A spend of vulnerable coins would trigger a contest: the highest bidder would receive the coins minus their bid, while the runner-up would pay their bid and receive nothing.
That structure could encourage escalating bids as participants try to avoid paying for no return. The intended deterrent is that an attacker might decline to start a contest that could cost more than the targeted coins are worth.
Preserving access does not mean removing risk
Another proposed response to quantum risk is to restrict spending from outdated wallets after a migration deadline. That could prevent theft, but it could also permanently exclude legitimate owners who had not moved their coins.
Fields’s ideas explore a different compromise: keep old coins potentially spendable, but make transfers costly and open to challenges. The underlying difficulty remains that Bitcoin cannot distinguish an owner from a quantum attacker when both can produce the same valid signature.
Large collateral requirements could burden legitimate holders. Inactive owners could miss a challenge window. Auction rules could destroy coins belonging to someone who is still alive but offline.
What would have to change
These proposals would first require a quantum-safe way to hold and spend Bitcoin. Wallets would need to support hidden ownership commitments, and consensus rules would need to enforce collateral, waiting periods, special recovery transactions and auctions.
Developers would also have to settle activation conditions, collateral amounts and the treatment of losing bids or remaining funds. Fields believes some mechanics could be introduced through a soft fork, but had not provided a detailed design.
At the time of publication, there was no implementation or activation schedule, and his post left auction payouts and even the intended auction outcome unresolved. For holders, the important distinction is between an exploratory proposal and a recovery feature that can actually be used: these mechanisms were not available in Bitcoin.
Source: Original Decrypt article, published November 8, 2026, at 22:01:03 UTC+08:00.