Insider Brief
- A quantum-resistant Bitcoin transaction has been completed on the Bitcoin mainnet using a method developed by StarkWare researcher Avihu Levy.
- The method uses signature grinding to limit exposure of public-key material while transactions wait in Bitcoin’s mempool, adding a quantum-resistant layer without changing Bitcoin’s existing cryptography.
- The transaction required direct submission to MARA’s Slipstream service because Bitcoin nodes do not currently relay its non-standard format, while Levy continues to support a protocol-level upgrade through a soft fork.
The first quantum-resistant Bitcoin transaction has been successfully executed.
A first-of-a-kind transaction on Bitcoin mainnet made funds that had been vulnerable to quantum attack now secure in the case of quantum attack. This challenges the long-held belief that only a fork can protect Bitcoin holdings against quantum.
The breakthrough comes amid rising concerns about quantum computing, especially in relation to Bitcoin. The method was devised by Avihu Levy, employee number one at StarkWare, and today head of the company’s applications division. Levy revealed his method earlier this year in a theoretical post– and now has put it to the test and proved that it actually works. He also just revealed that the breakthrough moment in his thinking happened in the shower (see below).
Bottom line: if a quantum computer strong enough to break Bitcoin cryptography arose tomorrow, the funds involved in this transaction would remain safe.
Context: This breakthrough is coming out of the crypto company that has emerged as a leader in post-quantum research. In parallel to work on this quantum-resistant transaction, in June StarkWare released crypto’s strongest quantum roadmap to date.
StarkWare’s CEO Eli Ben-Sasson said this illustrates that there are “lifeboats” to save Bitcoin from being “sunk” by quantum computers.
He commented: “This is dev culture at its most stunning. What started out as a passion project by Avihu during his evenings and weekends is now showing us that Bitcoin doesn’t have an expiry date and the critics are wrong.
“Bitcoin can and will be quantum-secure, and what we showed today is that this can happen even without a fork.”
Ben-Sasson stressed that he remains a strong advocate for a solution for quantum on a protocol level, but said that every step to prepare for quantum is important – and adds momentum to calls for a soft fork.
“A soft fork should happen, and I believe it will. But Avihu’s breakthrough is important because it gives the psychological reassurance which we need and which the asset itself needs. Namely, methods exist to secure Bitcoin.
“The important thing is that opportunities are seized. I’ve said before that crypto is behaving like passengers on the Titanic. What Avihu has illustrated is that there are lifeboats. That is not a reason to relax. It is a reason to build more of them, and to build them now.”
In an interview Levy just gave to the Quantum Bitcoin Countdown Podcast, he revealed how and when he realized that he could perform quantum-safe Bitcoin transactions: in the shower. He recalled that he was considering all hurdles that were being cited to securing Bitcoin “and I went in the shower and I was like… this is the missing puzzle. This is the missing piece of the puzzle for a quantum-safe Bitcoin transaction. And that’s it. Like it clicked and I just… went and wrote the whole thing. And from there, it was just the work of like, you know, putting all the pieces in place. But I already know what I’m doing.”
He told hosts Pete Rizzo and Nathan Jeffay: “I was asking can I actually make it a Quantum Safe Bitcoin transaction? And then it turned out I was saying ‘I think I can.’” The full episode of the pod, a co-production of Rizzo and StarkWare, is here.
Levy’s Method Explained
Levy’s method is available to all to read on GitHub. It does not interfere with any Bitcoin cryptography but rather adds the equivalent of an extra lock that defends holdings in the case of quantum attack. It uses signature grinding (explained below) to prevent use of public key material while transactions are in the Bitcoin mempool.
Levy said: “Bitcoin today relies on mathematical puzzles that Shor’s algorithm can solve almost instantly. A quantum computer could solve all the puzzles that secure Bitcoin. The Quantum-Safe Bitcoin method adds a second lock that a quantum computer has no shortcut for. It is forced to do the same long-form work as an ordinary machine — and that work is far beyond what any computer can do.”
The method closes Bitcoin’s exposed moment. Every transaction waits briefly in a public queue, the mempool, before it is confirmed, and while it waits it reveals the mathematical material a quantum computer would need to forge a signature and steal the funds first.
It closes that window using signature grinding. Rather than accept the first valid signature, the method generates candidates over and over — millions of times — until one appears with exactly the right shape: a form that does not expose that material while the transaction sits in the queue. The grinding is the brute-force search, and it is deliberately expensive. A single transaction takes hours of computing to produce.
The technique was largely inspired by Binohash, developed by BitVM creator Robin Linus.
Anyone can use the method — the code is public. But there is a catch for now. Bitcoin’s network only passes along transactions written in the standard formats it recognizes, and this one is unusual enough that ordinary nodes would simply ignore it. So instead of going into the public queue, it had to be handed straight to a miner willing to accept it. The mining company MARA runs a service, Slipstream, that does exactly that, and MARA mined this transaction. Anyone can now inspect it on the Bitcoin blockchain at https://mempool.space/tx/
A Necessary Safety Net
Levy consistently stresses that he favors securing Bitcoin via a protocol-level upgrade, but nonetheless points to the relevance of his research.
The Quantum-Safe Bitcoin method operates entirely on Bitcoin. Given that it doesn’t actually use StarkWare’s core technology, STARKs, some have asked how it came to be part of StarkWare’s repertoire. The answer is simple: passion.
Levy decided to search for the best quantum solution, whether using STARKs, which are themselves quantum secure, or another method. He is passionate about Bitcoin – so passionate that he spent his evenings and weekends doing this. Today, StarkWare is confronting the quantum threat with double power:
- The new QSB research
- STARKs, the core StarkWare technology, which are not used in the QSB method but which are post-quantum secure by design and will be part of the global roadmaps for quantum security. A plan to make Starknet quantum-secure is part of this.
StarkWare is also exploring how this framework can be used to construct quantum-resistant bridging technologies for strkBTC, a Starknet-issued wrapped Bitcoin asset with optional privacy, in the absence of a Bitcoin soft fork.
Readers can check out The Growing Quantum Security Challenge Facing Bitcoin and Digital Assets to expand their knowledge.
