StarkWare Researchers Complete First Quantum-Resistant Bitcoin Transaction, No Fork Required
A Bitcoin transaction that would survive an attack from a working quantum computer has now actually happened on mainnet — not in a lab, not in a whitepaper, but as a real transfer sitting in block 964,199. StarkWare, the Ethereum scaling firm better known for zero-knowledge proof systems, confirmed on August 26 that its researchers moved a 10,000-satoshi output using a method the team calls Quantum Safe Bitcoin, or QSB, and did it without touching a single line of Bitcoin’s consensus code.
The demonstration was put in front of a live audience a day later at the Bitcoin Asia conference in Hong Kong, where Damian Chen, VP of growth at the Starknet Foundation, walked attendees through how funds that would otherwise be exposed to a future quantum-capable adversary can be locked down using nothing but rules already built into Bitcoin today.
The Problem QSB Is Trying to Solve
Bitcoin’s signature scheme, ECDSA, is considered safe against classical computers but theoretically breakable by a sufficiently powerful quantum machine, since a public key exposed on-chain can, in principle, be used to derive its matching private key via Shor’s algorithm. In practice, a public key is only revealed at the moment a transaction is broadcast and sits in the mempool before confirmation — a narrow but real window of exposure that has worried cryptographers for years.
How Signature Grinding Closes the Window
The method behind QSB was designed by Avihu Levy, StarkWare’s General Manager of Applications, and carried to mainnet with engineering work from Tomer Giladi. Instead of accepting whatever signature a wallet first produces, the technique — called signature grinding — brute-forces through large numbers of candidate signatures until it finds one whose structure doesn’t leak the kind of public key material a quantum algorithm would need. Because the resulting transaction shape falls outside normal relay policy, it can’t simply be broadcast to the public mempool; the team worked with MARA’s Slipstream service to submit the transaction directly to a mining pool instead. StarkWare has described the cost of producing one such transaction as running into the several-hundred-dollar range — expensive by ordinary standards, but proof the technique works today, on Bitcoin as it currently exists.
Not a Fix, and StarkWare Says So
StarkWare has been careful to frame this as a proof of concept rather than a solution. CEO Eli Ben-Sasson said the team still wants to see Bitcoin adopt a proper soft fork for quantum resistance and expects one eventually will pass, calling Avihu Levy’s after-hours side project evidence that “Bitcoin has no expiration date.” On social media, Ben-Sasson went further, warning that the achievement “should not be viewed as a message saying Bitcoin is prepared for the quantum threat” — the technique protects only transactions that use it deliberately, not the roughly one-fifth of all bitcoin sitting in older addresses with already-exposed public keys.
This is a different milestone from the quantum-security conversations coin680 has covered recently, including the US Treasury’s quantum-readiness task force and a separate signature-scheme proposal circulating among Bitcoin developers. Those are policy and protocol discussions about what Bitcoin should eventually do. QSB is a working demonstration of what a determined engineer can already do without waiting for any of that to happen — a distinction StarkWare itself is keen to preserve.
Whether QSB sees any real adoption before an actual quantum threat materializes is an open question; the computational cost alone makes it impractical for routine use. But as a proof that Bitcoin’s existing script language has more defensive flexibility than most assumed, it has already done its job.
Curious how Bitcoin’s underlying script and signature system actually works? Coin680’s Bitcoin Academy breaks down the fundamentals in plain language.
This article is for informational purposes only and does not constitute financial or investment advice. Cryptocurrency markets are highly volatile and technical developments like this one carry uncertain real-world impact — always do your own research before making investment decisions.