If future Bitcoin (BTC) rules follow developer Cory Fields’ thought experiment, holders of vulnerable coins would need to lock up extra funds to spend them, adding a deterrent to quantum theft.
Fields described the idea as a “quantum landmine” in a Nov. 4 post to Bitcoin’s development mailing list. The scenario assumes quantum-safe outputs exist before q-day and new validation rules activate after it. He left soft-fork implementation for future work; the 30-day interval is illustrative.
The example starts with 1 BTC in a vulnerable output and 1 BTC in a quantum-safe one; those funds are spent together into a 2 BTC quantum-safe output. A separate, trivial quantum-safe output holds a prearranged proof that the owner knows the vulnerable coin’s private key.
An attacker moving the vulnerable BTC could put it in a time-locked output and would need 1 BTC in quantum-safe collateral. Without proof prepared before q-day, the attacker would have to wait through the example’s 30-day period before spending from that output again. During the wait, the original owner could reveal the proof, recover the vulnerable funds and claim the attacker’s collateral. The added risk is meant to deter attacks, but legitimate holders would also need quantum-safe funds to move vulnerable coins. Fields left the collateral ratio and timeout length undecided.
For outputs whose private keys are believed lost, Fields introduced a Staked Auction. One example uses a vulnerable 50 BTC output, a 40 BTC bid committed in advance and 50 BTC of attacker collateral. He also described a Sats Auction as an alternative that would not require staking before q-day, drawing on the Dollar Auction game suggested by Neha Narula. Fields left the auction terms and outcomes unresolved.
