coindesk.com
A Bitcoin Core developer wants to make future quantum thieves risk their own money before they can steal anyone else’s.
Cory Fields, who works on Bitcoin’s software at MIT’s Digital Currency Initiative, outlined the idea Wednesday on the bitcoin-dev mailing list. His “quantum landmines” would let holders secretly prepare a trap for anyone who later cracks their wallet keys.
A sufficiently powerful quantum computer could calculate a wallet’s secret spending key from its public key. Some early bitcoin payments exposed those public keys from the start, leaving coins associated with Satoshi Nakamoto among the potential targets.
CoinDesk has previously explored the dispute over whether Bitcoin should freeze vulnerable coins or leave them available to whoever can produce a valid signature. A freeze could stop thieves while also locking out owners who never upgraded.
How the proposed technique works
Fields would attach a financial penalty to trying. Under his example, stealing 1 $BTC would require the attacker to supply another 1 $BTC from a quantum-safe wallet. Both coins would then be locked for a waiting period, such as 30 days.
Before quantum attacks become possible, the original owner could create a separate quantum-safe “landmine” containing hidden proof of ownership of coins. If a thief later tries to drain vulnerable coins, both the stolen bitcoin and the thief’s collateral would be locked for a waiting period. During that time, the owner could reveal the proof, reclaim their bitcoin and take the thief’s collateral as a penalty.
The thief would have no way to tell which holdings contained a trap before committing their own money.
The scheme, therefore, gives owners an incentive to set traps before quantum computers become a threat. Alice could bait a quantum attacker pre-Q-day and double her vulnerable coins later, making quantum attackers wary of stealing coins as mines may secretly guard them.
“Because they have no pre-qday proof-of-knowledge of Alice’s key, the attacker would have to wait the 30 days before they can re-spend the output,” he said. “However, Alice notices the transaction in the meantime and spends the in-limbo output to her committed-to key by including her landmine as an input and revealing the proof. In doing so, she moves her own coins while also taking the attacker’s collateral.”
Caveat
Landmines only work for owners who still hold their keys, which rules out coins believed lost, Bitcoin creator Satoshi Nakamoto’s among them.
Fields sketched an auction system to protect those inactive coins from future quantum thieves. Under this plan, network rivals stake hidden bids on a vulnerable wallet in advance.
These bids act like cryptographic traps. If a quantum thief attacks, the highest bidder's smart contract triggers automatically, instantly burning or destroying the thief's target coins while seizing the thief's locked collateral and transferring it to the winning bidder as a bounty.
