- Quantum-safe Bitcoin transaction mined on mainnet without consensus changes.
- QSB enables quantum-resistant Bitcoin transactions on mainnet without a soft fork.
- High GPU costs and nonstandard transactions continue to limit QSB adoption.
A Bitcoin transaction designed to withstand a quantum-computing attack has been mined on mainnet without changing the network’s consensus rules. The transaction used Quantum-Safe Bitcoin (QSB), developed by Avihu Levy, head of StarkWare’s applications division, in collaboration with StarkWare engineer Tomer Giladi, and mined through MARA Foundation’s Slipstream service.
This moves QSB from an April 2026 research proposal to a live Bitcoin transaction while highlighting limits that researchers say still make protocol-level changes the preferred long-term approach.
QSB Uses Existing Bitcoin Rules to Add a Hash-Based Lock
Levy’s QSB layout builds on BINOHASH and replaces a non-quantum-safe component with a hash-to-signature puzzle based on RIPEMD-160 pre-image resistance. The paper estimates about 118 bits of second-preimage resistance under its Shor threat model, with lower effective security under Grover’s algorithm.
The construction works within Bitcoin’s existing script limits and does not require a soft fork. Instead, the sender performs computational work offchain to find a spending transaction whose hash satisfies Bitcoin’s signature-format requirements. The transaction then depends on hash security rather than only elliptic-curve signatures.
However, the process remains costly. Levy estimated offchain GPU expenses at several hundred dollars per transaction. QSB transactions are also nonstandard, meaning they do not move through Bitcoin’s ordinary mempool and currently require a direct mining route.
Researchers Highlight Limits for Exposed Bitcoin Public Keys
The method does not protect every Bitcoin output. Ivan Miskovic, founder of Quantum, noted that QSB only helps coins whose public keys have not already been revealed onchain. He cited roughly 1.7 million BTC held in P2PK outputs, as well as addresses with exposed public keys, as cases that cannot be protected by a no-fork scheme once exposed.
Levy agreed with the broader limitation. He said P2PK holders could theoretically move funds into QSB before a quantum attack, while higher-security modes may be possible at greater cost. He also described the design as a research prototype.
QSB Paper Still Favors Protocol-Level Quantum Protection
Section 1.3 of Levy’s paper calls QSB a “last-resort measure.” It says the approach does not yet scale across Bitcoin’s users, transaction values, and throughput, while also creating a more complex user experience.
The scheme also does not currently cover Lightning Network channels. The paper concludes that Bitcoin still needs research into a more efficient, user-friendly, quantum-resistant design implemented through protocol-level changes.
Related: Quantum-Safe Bitcoin: StarkWare’s New ‘No Soft Fork’ Defense
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