StarkWare researcher Avihu Levy has successfully executed an experimental quantum-resistant transaction on the Bitcoin blockchain, marking what the company described as a first-of-its-kind achievement.
Quantum Safe Bitcoin tested on mainnet
The transaction, which took place in Bitcoin block 964,199, utilized Levy’s Quantum Safe Bitcoin (QSB) scheme to spend a 10,000-satoshi output. Block confirmation was carried out by MARA Pool, which accessed the transaction via its Slipstream service, due to the nonstandard structure of the QSB format.
Levy’s repository defines QSB as a mechanism that combines hash-based one-time signatures with computational searches that link transaction authorization to a specific action. This construction is designed to prevent transaction forgery even in the event that quantum computers can break Bitcoin’s present elliptic-curve cryptography.
By conducting this test, StarkWare moved the QSB method from theoretical discussion to practical, onchain demonstration, proving that Bitcoin’s consensus rules can handle at least one type of quantum-resistant transaction without the need for protocol upgrades.
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AAPLMini dictionary: StarkWare is a blockchain technology company focused on scaling and cryptographic security solutions for public blockchains, best known for its work on validity proofs and zero-knowledge rollups.
Quantum risks and costs
Concerns about quantum computers’ future ability to compromise Bitcoin keys resurfaced in March, when Google researchers estimated that a sufficiently advanced quantum machine might derive a Bitcoin private key in nine to 12 minutes after a public key becomes visible. This potential risk, they said, could allow attackers to replace pending transactions before full network confirmation.
In response, Levy proposed QSB in April, estimating at the time that a single quantum-resistant transaction would require $75 to $150 in GPU-based computation. According to StarkWare spokesperson Nathan Jeffay, the experimental transaction on the Bitcoin mainnet ultimately cost between $150 and $200 and required several hours of continuous computation.
StarkWare CEO Eli Ben-Sasson explained that, “A soft fork should happen, and I believe it will,” adding that QSB acts as a stopgap until protocol-level protections are ready.
Network integration and developer efforts
QSB transactions are currently categorized as nonstandard by Bitcoin Core’s relay policies. This classification means that ordinary Bitcoin nodes do not relay them, necessitating direct submission through specialized services like MARA’s Slipstream.
The QSB approach applies on a per-transaction basis and does not overhaul cryptography for the network as a whole. StarkWare emphasized that QSB is a contingency measure until broader protocol changes are implemented.
Bitcoin core developers are also evaluating other proposals to boost post-quantum protection for the network. These include BIP-360, a proposed soft fork that would introduce Pay-to-Merkle-Root outputs and eliminate Taproot’s quantum-exposed key-path spend.
The demonstration establishes that Bitcoin can host quantum-resistant payments without fundamental changes to consensus, at least through nonstandard transaction types.
| Feature | Quantum Safe Bitcoin (QSB) | Current Bitcoin Transactions |
|---|---|---|
| Protection Against Quantum Attacks | Yes (hash-based one-time signature) | No (elliptic-curve cryptography) |
| Network Relay | Nonstandard, requires direct submission | Standard, relayed by all nodes |
| Cost (Experimental Case) | $150-$200, hours of computation | Standard transaction fee, negligible computation |
| Protocol Change Required | No, within current consensus rules | No |
