Bitcoin confirms quantum-resistant transaction, but 7 million BTC may remain exposed

Bitcoin confirmed a quantum-resistant transaction on mainnet under its existing consensus rules. The transaction shows that some holders could migrate eligible funds before future quantum hardware threatens exposed keys. The Aug. 26 transaction used a construction developed by StarkWare researcher Avihu Levy. The transaction appeared in block 964,199. Levy submitted it directly to Bitcoin miner MARA through its Slipstream service. StarkWare described the transaction as the first quantum-safe spend on Bitcoin mainnet. The Quantum-Safe Bitcoin, or QSB, construction shifts the critical spending condition from elliptic-curve signatures to hash-based security. QSB repeatedly varies candidate transaction data until it produces a hash that Bitcoin accepts as a validly formatted signature. The computation occurs before the transaction is broadcast. QSB may provide a migration path for coins whose public keys remain hidden. The construction does not protect coins whose public keys are already visible. Those coins include older pay-to-public-key outputs, Taproot outputs, and reused addresses. Roughly 7 million BTC are considered potentially vulnerable through those address formats or practices. QSB is nonstandard under default Bitcoin node policy. Transactions using QSB will not normally propagate through the public mempool. StarkWare sent the test transaction directly to MARA through Slipstream because of that limitation. StarkWare said the mainnet test cost several hundred dollars. The project's open-source repository estimates costs of roughly $75 to $150 for some configured cloud-GPU search phases. StarkWare Chief Executive Eli Ben-Sasson said the test does not show that Bitcoin is already prepared for quantum computing. Ben-Sasson said broader soft-fork solutions are still needed to protect the network at scale. In July, BlackRock, Coinbase, Strategy, and six other institutions formed the Bitcoin Security Consortium. The members pledged a combined $15 million over three years for Bitcoin security research, including post-quantum cryptography. The members direct that funding independently rather than through a common pool. The US Treasury has included digital assets in broader financial-sector quantum-readiness planning. Bitcoin still needs migration tools for holders whose public keys remain hidden. Bitcoin also needs a protocol-level solution for coins whose keys are already exposed.