StarkWare Confirms First Quantum-Safe Bitcoin Transaction
StarkWare says a Bitcoin transaction using its Quantum Safe Bitcoin design was confirmed on mainnet without requiring changes to Bitcoin’s consensus rules.
Bitcoin developers have taken an early step toward addressing one of the network’s long-term security challenges: the potential threat posed by sufficiently powerful quantum computers.
A transaction using Quantum Safe Bitcoin (QSB), a design developed by StarkWare researcher Avihu Levy, was confirmed on the Bitcoin mainnet on Aug. 26. The transaction spent a 10,000-satoshi output protected using the QSB construction and was included in block 964,199.
MARA Pool mined the transaction after receiving it through its Slipstream service. StarkWare described the event as the first quantum-safe Bitcoin transaction, although the onchain confirmation itself demonstrates that the construction was accepted by Bitcoin rather than independently proving its resistance to quantum attacks.
How QSB Works on Bitcoin
Bitcoin currently relies on elliptic curve cryptography for digital signatures. That system remains secure against conventional computers, but a sufficiently capable quantum computer running Shor’s algorithm could theoretically derive a private key from its corresponding public key.
Many Bitcoin addresses reduce exposure by keeping the public key hidden behind a hash until coins are spent. Once a transaction is broadcast, however, the public key becomes visible while the transaction waits for confirmation. A future quantum attacker could potentially exploit that window to recover the private key and attempt to spend the same coins first.
QSB approaches the problem by adding a quantum-resistant lock based on hash functions rather than relying solely on elliptic curve cryptography.
The design uses a technique known as signature grinding, which searches computationally for a spending transaction whose hash can function as a validly formatted Bitcoin signature. The required computation takes place offchain before the transaction is broadcast.
As a result, the construction shifts its security toward the difficulty of reversing a hash. According to the research, the process currently costs several hundred dollars and draws heavily on Binohash, a technique developed by BitVM creator Robin Linus.
Crucially, QSB works with Bitcoin as it exists today, without modifying its consensus rules.
The Experiment Has Important Limitations
The successful transaction does not mean Bitcoin has become quantum-resistant. Instead, it demonstrates that a specific hash-based construction can operate on the existing network.
QSB protects coins by moving them into an output secured through hashes rather than elliptic curves. It would not protect funds whose public key had already been exposed before the QSB transaction was broadcast, since a sufficiently powerful quantum adversary could theoretically derive the corresponding private key beforehand.
There is also an infrastructure limitation. QSB transactions currently use nonstandard formats, meaning they cannot propagate through Bitcoin’s ordinary mempool. The test therefore required a direct route to a miner, provided by MARA’s Slipstream service.
Levy designed QSB and published the underlying research in April 2026 after developing the concept independently in his spare time. StarkWare engineer Tomer Giladi later helped advance the work toward a functioning mainnet transaction.
StarkWare’s Broader Post-Quantum Push
Although StarkWare is best known for ZK-STARKs, QSB does not use STARK proofs. Instead, Levy designed the method entirely around capabilities already available within Bitcoin.
The experiment nevertheless fits into StarkWare’s broader work on preparing blockchain infrastructure for a post-quantum future. ZK-STARKs themselves rely on hash-based security rather than elliptic-curve assumptions, giving Starknet a foundation for introducing quantum-resistant cryptography.
Starknet also uses native account abstraction, allowing accounts to change their signature schemes without requiring a protocol-wide upgrade. Post-quantum accounts are already live on Starknet mainnet, according to StarkWare.
However, Starknet is not fully quantum-ready. StarkWare published a three-phase roadmap in June covering new activity, existing contracts and dependencies inherited from Ethereum. Some components of the first phase have already shipped, while other upgrades remain outstanding.
A Proof of Concept for Bitcoin’s Quantum Future
StarkWare CEO Eli Ben-Sasson said the experiment could provide Bitcoin holders with an additional path to protection while broader protocol changes are considered.
“Avihu took this on after hours, as a passion project, and has now shown that Bitcoin has no expiration date. I still want Bitcoin to choose to do a soft fork and I expect we will get one. What today’s successful transaction offers Bitcoin is a reassurance that holdings can be protected before that happens.”
The transaction is best viewed as an early proof of concept rather than a complete quantum-security solution for Bitcoin. It shows that developers can potentially authorize certain Bitcoin transactions using cryptographic techniques intended to withstand future quantum attacks without immediately changing the network’s consensus rules.
At the same time, its limitations underscore why protocol-level migration remains an important long-term question. As quantum computing advances, experiments such as QSB could help establish practical options for protecting digital assets while the Bitcoin ecosystem evaluates broader changes to its cryptographic foundations.
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