StarkWare Executes First Quantum-Safe Bitcoin Transaction on Mainnet

StarkWare said Wednesday it had completed the first quantum-safe Bitcoin transaction on mainnet, a spend built to hold up against an adversary running a working quantum computer. Onchain data shows the transaction confirmed in block 964,199 and spent a 10,000-satoshi output protected by the scheme. Bitcoin’s consensus rules were not touched.

The method is Quantum-Safe Bitcoin, or QSB, designed by Avihu Levy, StarkWare’s general manager of applications, who published the research in April. StarkWare engineer Tomer Giladi carried the work through to a live transaction. Because QSB transactions use nonstandard formats, ordinary nodes will not propagate them, so the transaction went directly to a miner through MARA’s Slipstream service.

The threat QSB addresses is not theft from untouched cold storage but the window that opens every time a holder spends. Most Bitcoin addresses are hashes of a public key, so the key stays hidden until a signature reveals it, and the transaction then sits in the mempool in the open until a miner includes it. A quantum adversary could read the public key in that window, derive the private key and spend the coins first. QSB adds a second lock built on hash functions, which Shor’s algorithm cannot break, giving custodians a spend path they can provision now instead of waiting on a protocol change.

The economics remain punishing. Signature grinding requires the sender to burn offchain compute searching for a spending transaction whose hash happens to form a validly formatted signature, drawing on Binohash from BitVM creator Robin Linus. StarkWare put the cost of the completed mainnet spend at several hundred dollars and hours of computation. QSB also cannot protect an address whose public key is already onchain.

StarkWare framed the result as reassurance rather than a fix. CEO Eli Ben-Sasson said he still wants Bitcoin to adopt a soft fork and expects one, describing Levy’s method as a safety net until protocol-level protections arrive. Levy holds the same position, and his April paper framed the scheme as a last resort.

Related Listen: One Type of Post-Quantum Cryptography Is Most Popular. Why Is Crypto Trying Out Three?

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