The first quantum-resistant Bitcoin transaction has now been carried out on mainnet. StarkWare announced the transaction was confirmed on Wednesday, August 26, in block 964,199, moving a 10,000-satoshi output using a method the company calls Quantum Safe Bitcoin (QSB). It worked within Bitcoin’s existing rules, so no protocol change was needed.
Inside the Quantum-Safe Method
StarkWare researcher Avihu Levy built QSB around a technique known as signature grinding. Instead of accepting the first valid signature a wallet generates, the method searches through millions of candidate signatures until it finds one that does not expose the kind of public key information a quantum computer could exploit while a transaction sits in the mempool waiting to confirm.
The math behind QSB leans on the strength of RIPEMD-160, a hashing function, rather than the elliptic-curve cryptography that secures ordinary Bitcoin transactions today.
StarkWare’s repository estimates the approach offers roughly 118-bit resistance against an attacker running Shor’s algorithm, the quantum method that could theoretically reverse-engineer a private key from a public one.
MARA Pool mined the block after receiving the transaction directly through its Slipstream service, since regular Bitcoin nodes do not relay this nonstandard transaction type on their own.
The Limitations StarkWare Acknowledged
There’s an important catch here. QSB protects one transaction at a time, not the whole network. It only works with older, pre-SegWit style addresses, and it does nothing for Taproot outputs or Lightning Network channels.
Coins still have to pass through a normal transaction to reach a QSB-protected output first, which briefly exposes the same public key information the method is designed to hide.
No quantum computer capable of breaking Bitcoin’s cryptography exists yet. StarkWare CEO Eli Ben-Sasson described the test as reassurance that a defense is possible, not a signal that the threat has arrived.
If quantum computing is new territory for you, our guide on how quantum computing threatens crypto holdings breaks down the basics in plain terms, and our wallet security guide covers the security practices that matter regardless of what happens with quantum computing.
What Comes Next
Levy has called QSB a last-resort measure, not a permanent solution. StarkWare CEO Eli Ben-Sasson has pointed to BIP-360 as the path toward a real fix, since it would upgrade Bitcoin’s cryptography at the protocol level rather than protecting one transaction at a time. Independent review of the QSB code and further mainnet testing are expected to follow.
What This Means for You: Nothing about your Bitcoin holdings changes today. You won’t find QSB as an option on Coinbase or your hardware wallet anytime soon, and it costs far more than an ordinary transaction fee to use. What it does show is that Bitcoin’s existing rules can support at least one form of quantum defense without a network split, giving developers more room to design a permanent fix.
