StarkWare researcher Avihu Levy has tested an experimental quantum-resistant transaction on the Bitcoin mainnet — the company calls it the first of its kind.
According to StarkWare, the transaction was confirmed on Wednesday in Bitcoin block 964,199. On-chain data shows it spent an output of 10,000 satoshis protected by Levy's Quantum Safe Bitcoin (QSB) scheme; the block was mined by MARA Pool after receiving the transaction via its Slipstream service.
Levy's paper and code repository state that QSB combines hash-based one-time signatures with a computational search that ties authorization to a specific transaction. The design aims to prevent forgery even if a quantum computer breaks the elliptic curve cryptography used by Bitcoin.
The test moves Levy's April proposal from theory to an on-chain demonstration and shows that Bitcoin's existing consensus rules allow for one type of quantum-resistant spending without a protocol change.
Bitcoin's quantum-resistant method remains expensive
In March, Google researchers estimated that a sufficiently powerful quantum computer could theoretically derive a Bitcoin private key within nine to 12 minutes after its public key becomes visible. Google stated this could allow an attacker to replace a pending transaction within Bitcoin's confirmation window.
Levy then presented QSB in April, estimating at the time that creating a transaction would require $75 to $150 worth of GPU computations. He described it as an emergency measure, not a replacement for protocol-level safeguards.
A StarkWare spokesperson, Nathan Jeffay, told Cointelegraph that the completed transaction cost "several hundred dollars," estimating the expense at roughly $150–200. The StarkWare release states the computation took several hours.
Related: Banks and regulators join pilot for quantum-resistant crypto transfers
Levy's repository also classifies QSB transactions as non-standard under default Bitcoin Core relay policies. StarkWare said this is why regular nodes would not have relayed the transaction until it was confirmed, necessitating its direct transmission via the MARA Slipstream service.
QSB applies to individual Bitcoin transactions, rather than updating the cryptography for the entire network. "A soft fork will need to happen, and I believe it will," said StarkWare CEO Eli Ben-Sasson, adding that QSB serves as a safety net during the development of protocol-level protections.
Bitcoin developers are separately considering proposals, including BIP-360 — a proposed soft fork that would introduce a Pay-to-Merkle-Root output type while simultaneously removing the quantum-vulnerable key-path spend for Taproot.
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