StarkWare researcher Avihu Levy has tested an experimental quantum-resistant transaction on the Bitcoin mainnet, marking what the company described as the first transaction of its kind. According to StarkWare, the transaction was confirmed in Bitcoin block 964,199.
Onchain data shows the transaction spent a 10,000-satoshi output protected by Levy’s Quantum Safe Bitcoin (QSB) scheme. The block was mined by MARA Pool after receiving the transaction through its Slipstream service.
Levy’s paper and code repository state that QSB combines hash-based one-time signatures with computational searches that bind an authorization to a specific transaction. This construction is designed to prevent forgery even if a quantum computer breaks the elliptic-curve cryptography currently used by Bitcoin. The test transitions Levy’s April proposal from theory to an onchain demonstration, showing that Bitcoin’s existing consensus rules can accommodate this form of quantum-resistant spending without requiring a protocol change.
Costs and Network Considerations
In March, Google researchers estimated that a sufficiently capable quantum computer could theoretically derive a Bitcoin private key nine to 12 minutes after its public key becomes visible, potentially allowing an attacker to replace a pending transaction during the confirmation window. Following this, Levy introduced QSB in April.
While the method offers a defense mechanism, it remains costly. StarkWare spokesperson Nathan Jeffay stated that the completed transaction cost in the low hundreds of dollars, estimated between $150 and $200, with StarkWare noting the process required hours of computation.
Additionally, Levy’s repository classifies QSB transactions as nonstandard under Bitcoin Core’s default relay policies. As a result, ordinary nodes do not propagate the transaction before confirmation, necessitating direct submission through MARA’s Slipstream service.
Broader Quantum Safety Efforts
QSB applies to individual Bitcoin transactions rather than upgrading cryptography across the entire network. StarkWare CEO Eli Ben-Sasson stated that a soft fork should happen and that QSB provides a safety net while protocol-level protections are developed.
Separately, Bitcoin developers are considering proposals such as BIP-360, a proposed soft fork that would introduce a Pay-to-Merkle-Root output type while removing Taproot’s quantum-vulnerable key-path spend.
