StarkWare says it has pulled off the first quantum-resistant Bitcoin transaction ever confirmed on the network’s main chain, a milestone the company frames as proof that Bitcoin can defend itself against future quantum attacks without rewriting its rulebook. The transaction landed in block 964,199 on Wednesday, August 26, moving a 10,000-satoshi output through a method StarkWare calls Quantum Safe Bitcoin, or QSB. No soft fork, no hard fork, no protocol change — just a clever workaround built on top of Bitcoin as it exists today.
Key takeaways
- StarkWare confirmed the first quantum-resistant Bitcoin transaction on mainnet in block 964,199, moving a 10,000-satoshi output.
- The Quantum Safe Bitcoin (QSB) method uses signature grinding and RIPEMD-160 hashing instead of elliptic-curve cryptography, offering roughly 118-bit resistance against Shor’s algorithm.
- QSB only protects one transaction at a time, works solely with older pre-SegWit addresses, and does not support Taproot or the Lightning Network.
- No quantum computer today can break Bitcoin’s cryptography; StarkWare calls QSB a stopgap while it pushes BIP-360 as the real long-term fix.
- QSB is not available on mainstream wallets or exchanges yet and costs significantly more than a standard Bitcoin transaction fee.
Landmark Quantum-Resistant Bitcoin Transaction on Mainnet
The headline fact is simple: a working, mined transaction now exists that was built specifically to resist a quantum attack, and it happened without any changes to Bitcoin’s consensus rules. That distinction matters more than it sounds. Much of the debate around quantum threats to Bitcoin has assumed the network would eventually need a contentious fork to defend itself. StarkWare’s demonstration pushes back on that assumption, at least for individual transactions.
Getting the transaction onto the chain wasn’t straightforward, though. Because QSB produces a nonstandard transaction format, ordinary Bitcoin nodes wouldn’t relay it on their own. StarkWare had to hand the transaction directly to MARA Pool, which mined the block after receiving it through its Slipstream service — a route miners use to accept transactions that don’t fit the network’s standard templates. Without that direct path to a willing miner, the transaction likely would have sat unconfirmed indefinitely.
Technical Innovations Behind Quantum Safe Bitcoin
QSB works by rethinking how a Bitcoin signature gets generated, not by changing what a signature is. StarkWare researcher Avihu Levy built the method around a technique called signature grinding: rather than accepting the first valid signature a wallet produces, the process runs through millions of candidate signatures until it finds one that avoids exposing the type of public key data a quantum computer could theoretically exploit while a transaction waits in the mempool.
That waiting period is the actual vulnerability. Once a transaction is broadcast but not yet confirmed, it briefly reveals mathematical information tied to the sender’s public key. A sufficiently powerful quantum machine running Shor’s algorithm could, in theory, use that exposure window to forge a signature and hijack the funds before confirmation. QSB is designed to close that gap by leaning on the strength of RIPEMD-160 hashing instead of the elliptic-curve cryptography that underpins ordinary Bitcoin transactions. StarkWare’s own repository estimates the approach delivers roughly 118-bit resistance against a quantum attacker — a meaningful cushion, though the process is computationally expensive and can take hours of processing to produce a single transaction.
Limitations and Security Considerations of QSB
QSB is not a network-wide fix, and StarkWare has been upfront about that. The method protects one transaction at a time rather than securing Bitcoin as a whole, and it only works with older, pre-SegWit style addresses. That means it offers nothing for Taproot outputs or Lightning Network channels, which cover a large share of Bitcoin activity today.
There’s also a structural catch built into how coins reach a QSB-protected output in the first place. Coins still have to move through a normal transaction before they land in a QSB-shielded state, and that ordinary step briefly exposes the same kind of public key information QSB is meant to hide. In other words, the protection only kicks in after a small window of exposure has already passed — a limitation StarkWare acknowledges rather than downplays.
Current Quantum Threats and Future Cryptographic Upgrades
No quantum computer capable of breaking Bitcoin’s cryptography exists right now, and StarkWare has been careful not to suggest otherwise. StarkWare CEO Eli Ben-Sasson described the demonstration as reassurance that a defense is possible, not evidence that an attack is imminent. He put it more colorfully in comments reported by The Block, comparing the crypto industry to passengers on the Titanic and calling Levy’s method proof that “lifeboats” exist. “That is not a reason to relax,” Ben-Sasson said. “It is a reason to build more of them, and to build them now.”
Levy himself has called QSB a last-resort measure rather than a lasting solution, and Ben-Sasson has pointed to BIP-360 as the real path forward — a proposed protocol-level upgrade that would rework Bitcoin’s cryptography for the entire network instead of shielding transactions one at a time. Independent review of the QSB code and additional mainnet testing are both expected to follow before the method sees any broader use. Why does this distinction matter? Because a transaction-by-transaction workaround buys time, but it doesn’t scale to millions of addresses the way a protocol upgrade eventually would.
User Accessibility and Practical Implications Today
For everyday Bitcoin holders, nothing changes yet. QSB isn’t available through Coinbase, a hardware wallet, or any other mainstream service, and using it costs far more than a standard Bitcoin transaction fee because of the heavy computation signature grinding requires. StarkWare’s own framing acknowledges this: QSB is a proof of concept aimed at custodians and developers, not a consumer-ready tool.
What the transaction does demonstrate is that Bitcoin’s existing rules can accommodate at least one form of quantum defense without triggering a network split. That gives developers breathing room to keep refining a permanent fix — whether that ends up being BIP-360 or some other approach — while the underlying quantum threat, still theoretical for now, continues to loom over the industry’s longer-term planning.
FAQ
What is the significance of StarkWare’s quantum-resistant Bitcoin transaction?
It demonstrates the first quantum-resistant Bitcoin transaction on mainnet, showing Bitcoin’s existing rules can support quantum defense without protocol changes.
How does Quantum Safe Bitcoin (QSB) improve Bitcoin security against quantum attacks?
QSB uses signature grinding and RIPEMD-160 hashing to minimize public key exposure, offering about 118-bit resistance against quantum attacks using Shor’s algorithm.
What are the limitations of QSB for users today?
QSB only protects one transaction at a time, works with pre-SegWit addresses, is not supported by Taproot or Lightning Network, is costlier, and not yet available in popular wallets or exchanges.
Is Bitcoin currently at risk from quantum computers?
No existing quantum computer can break Bitcoin’s cryptography today, but QSB and future protocol upgrades like BIP-360 prepare the network for potential future threats.
Article produced with the assistance of artificial intelligence and reviewed by the editorial team.
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