StarkWare Moves 3.1 Bitcoin in What It Calls the First Quantum-Safe Mainnet Spend

StarkWare confirmed a bitcoin transaction that it says a future quantum computer could not forge, and it accomplished this without any change to Bitcoin's consensus rules. The company moved 3.1 bitcoin using a scheme called Quantum Safe Bitcoin (QSB), designed by StarkWare chief product officer Avihu Levy. QSB replaces the elliptic-curve signature that normally authorizes a bitcoin spend with a one-time signature built only from hash functions and written in Bitcoin's existing scripting language. Cointelegraph reported the same result, calling it the first such transaction on the live network.

The design matters more than the amount moved. Every bitcoin today is protected by elliptic-curve signatures, which a sufficiently powerful quantum computer running Shor's algorithm could break. QSB avoids the need for a soft fork, the network-wide rule change a new signature type would normally require, by shifting the cost to computation instead. Levy's published work relies on extensive off-chain proving, and CoinDesk reported in April that the method costs roughly $75 to $200 per transaction.

On the same day, Ethereum core developers filed a draft Ethereum Improvement Proposal (EIP) that would let validators deposit using quantum-resistant keys and then permanently stop accepting the key format the network uses now, CoinDesk reported. The draft currently carries a placeholder number, though a repository maintainer suggested it be assigned EIP-8394. It is part of the Lean Consensus effort, which is developing leanXMSS, a hash-based signature scheme for validators.

The replacement candidates are not settled. Blockstream Research graded the three leading lattice-based signature schemes proposed for Bitcoin, Falcon, Dilithium and Hawk, and one of the three was withdrawn before the report was finished.