StarkWare announced Wednesday that a quantum-safe Bitcoin transaction has been successfully mined on the live network, marking a first for the method.
On-chain data shows the transaction spent a 10,000-satoshi output, worth about $8, and paid a fee of 5,179 satoshis. The transaction was built in collaboration with MARA Foundation and StarkWare researchers, and was subsequently mined by MARA Pool in block 964,199.
The underlying method, known as Quantum-Safe Bitcoin (QSB), was published in April by StarkWare researcher Avihu Levy. It attaches a hash-based lock beside the elliptic curve signature that normally guards a Bitcoin output. Because Shor's algorithm—the quantum technique used to derive private keys from published public keys—cannot break hash functions, security rests on reversing a hash rather than keeping a private key secret. The technique builds on Binohash, which was developed by BitVM creator Robin Linus.
The process uses signature grinding, where the sender grinds off-chain until a candidate spending transaction hashes to a value that is itself a validly formatted signature. The test used a single construction rather than a network upgrade, leaving Bitcoin itself unchanged.
Limitations and Constraints
Despite the milestone, StarkWare noted that the method does not make Bitcoin quantum-safe, highlighting three major constraints:
- Prior exposure: Addresses whose public keys already sit on-chain gain no protection, as a quantum adversary could still derive the corresponding private key.
- Migration step: Coins reach a hash-secured output through a transaction signed the ordinary way, which exposes the sending address's public key. For instance, the output spent in this test was funded in July by such a transaction.
- Delivery: Because QSB transactions use nonstandard formats, ordinary nodes will not relay them. MARA's Slipstream service was required to supply the route to a miner.
High costs also compound these limits. StarkWare described the transaction as costing several hundred dollars, while Levy's repository estimates offchain compute costs between $75 and $150.
While StarkWare has consistently argued that a soft fork remains the better long-term answer, the company stated that this demonstration proves protocol changes are no longer the only option. Bitcoin has not adopted a protocol-level fix, and the recent transaction does not alter that status.
