CryptoSlate
On Aug. 26, a transaction in Bitcoin block 964,199 spent coins through a hash-based spending path designed by StarkWare researcher Avihu Levy, marking what StarkWare called the first quantum-safe spend on Bitcoin mainnet. The Quantum-Safe Bitcoin, or QSB, construction moves the critical spending condition away from elliptic-curve signatures and toward hash-based security, exploiting the window between address creation and public-key reveal. The transaction is nonstandard under default node policy, so StarkWare had it submitted directly to miner MARA through its Slipstream service rather than broadcasting it through the public mempool.
Why it matters
StarkWare CEO Eli Ben-Sasson was quick to draw the line. The test proves workable approaches exist for coins whose public keys remain hidden, he said, but it does not mean Bitcoin is prepared for quantum computing. The harder problem sits in older pay-to-public-key outputs, Taproot outputs, and reused addresses, where the public key is already visible. Roughly 7 million BTC are estimated to sit in those categories, and QSB offers no migration path for any of them.
Market impact
In July, BlackRock, Coinbase, Strategy, and six other institutions formed the Bitcoin Security Consortium and pledged $15 million over three years toward Bitcoin security research, including post-quantum cryptography. Members direct the funding independently rather than through a common pool. The US Treasury has also folded digital assets into broader financial-sector quantum-readiness planning. On cost, the Aug. 26 mainnet test ran several hundred dollars per transaction, with cloud-GPU search phases in the $75-$150 range. That keeps QSB in the niche-escape-hatch category rather than a wallet-default option, leaving broader soft-fork migration as the open question for the millions of BTC still exposed.
Frequently asked questions
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What is QSB and how does it protect Bitcoin from quantum attacks?
Quantum-Safe Bitcoin (QSB) is a construction by StarkWare researcher Avihu Levy that shifts the spending condition from elliptic-curve signatures to hash-based security. It varies candidate transaction data until it produces a hash Bitcoin accepts as a valid signature format, shifting the security assumption away from…
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Why can't QSB protect all Bitcoin holders from quantum risk?
QSB only protects coins whose public keys remain hidden behind a hash until they are spent. About 7 million BTC sit in older pay-to-public-key outputs, Taproot, and reused addresses where the public key is already exposed, leaving those coins without a working migration path.
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How was the first quantum-safe Bitcoin transaction submitted?
The Aug. 26 transaction in block 964,199 was submitted directly to miner MARA through its Slipstream service because the QSB transaction is nonstandard under default node policy and would not propagate through the public mempool on its own.
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What is the Bitcoin Security Consortium and what does it fund?
Formed in July, the consortium includes BlackRock, Coinbase, Strategy, and six other institutions, which together pledged $15 million over three years toward Bitcoin security research including post-quantum cryptography. Members direct the funding independently rather than through a common pool.
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What did StarkWare's CEO say about Bitcoin's quantum readiness?
Eli Ben-Sasson warned the test should not be read as evidence Bitcoin is prepared for quantum computing. He argued it only proves workable approaches exist and that broader soft-fork solutions are still needed to protect the network at scale.
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