StarkWare tests a quantum-resistant Bitcoin transaction on mainnet

A Bitcoin transaction confirmed this week looks ordinary on a block explorer, but StarkWare says it's the first of its kind: a quantum-resistant spend executed directly on Bitcoin mainnet, no protocol change required, Cointelegraph reported.

StarkWare researcher Avihu Levy ran the test, and the transaction confirmed Wednesday in block 964,199. Onchain data shows it spent a 10,000-satoshi output protected by Levy's Quantum Safe Bitcoin scheme, known as QSB, with MARA Pool mining the block after receiving the transaction through its Slipstream service.

QSB combines hash-based one-time signatures with computational searches that bind an authorization to a specific transaction, according to Levy's paper and code repository. The construction aims to stop forgery even if a quantum computer eventually breaks the elliptic-curve cryptography Bitcoin currently relies on. The mainnet test turns Levy's April proposal from a paper design into a working demonstration, and it shows Bitcoin's existing consensus rules can already accommodate one form of quantum-resistant spending without any soft fork or hard fork.

The urgency behind the work traces back to March, when Google researchers estimated that a sufficiently capable quantum computer could theoretically derive a Bitcoin private key nine to 12 minutes after its public key becomes visible. Google said that timeline could let an attacker swap in a fraudulent transaction during Bitcoin's confirmation window, the gap between broadcast and burial under enough blocks to consider a payment final.

Levy introduced QSB in April, estimating then that generating a single transaction would cost between $75 and $150 in GPU computation, and he described it as a last-resort measure rather than a substitute for protocol-level fixes. That estimate held up close to reality: StarkWare spokesperson Nathan Jeffay told Cointelegraph the completed transaction cost "low hundreds of dollars," landing around $150 to $200, with the underlying computation taking hours.

• Block confirmed: 964,199
• Amount spent: a 10,000-satoshi output
• Miner: MARA Pool, via its Slipstream service
• Computation cost: roughly $150 to $200, taking hours to generate
• Google's March estimate: a quantum computer could derive a private key in 9 to 12 minutes after key exposure

The method has a real limitation baked in. Levy's repository classifies QSB transactions as nonstandard under Bitcoin Core's default relay policies, so ordinary nodes won't propagate them before confirmation. That's why the transaction had to go straight through MARA's Slipstream service instead of the normal mempool.

QSB protects individual transactions rather than upgrading Bitcoin's cryptography network-wide. Bitcoin developers are weighing broader fixes in parallel, including BIP-360, a proposed soft fork that would introduce a Pay-to-Merkle-Root output type while retiring Taproot's quantum-vulnerable key-path spend.

Intokened covered the funding side of this push earlier this month, when nine companies including BlackRock and Coinbase pledged $15 million to a Bitcoin security consortium working on quantum-proofing the network. Levy's mainnet transaction gives that effort something concrete to point to: proof that quantum resistance doesn't have to wait for a network-wide upgrade to start protecting individual coins today, even if the cost and friction make it a stopgap rather than a fix.

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