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StarkWare CPO Avihu Levy has published an open-source scheme to make Bitcoin transactions resistant to quantum computing attacks using only the network’s existing consensus rules, requiring no softfork, no protocol upgrade, and no community coordination. The project, called Quantum Safe Bitcoin (QSB), was released on April 9 by Avihu Levy, StarkWare’s chief product officer. It operates entirely within Bitcoin’s existing legacy Script constraints — 201 opcodes and a 10,000-byte limit — and achieves roughly 118 bits of security against Shor’s algorithm, the quantum computing attack that would render standard Bitcoin transactions effectively unprotected. The scheme replaces Bitcoin’s standard ECDSA signature mechanism with a hash-based construction that quantum computers can only attack using Grover’s algorithm, which offers a quadratic speedup rather than a total break. Off-chain computation runs between $75 and $150 in cloud GPU time per transaction, and the GPU work is publicly verifiable — private keys never leave the user’s device. This story is an excerpt from the Unchained Daily newsletter. Subscribe here to get these updates in your email for free The timing sharpens the stakes. A Google Quantum AI paper published on March 30 concluded that breaking Bitcoin’s elliptic-curve cryptography could require fewer than 500,000 physical qubits, a roughly 20-fold reduction from earlier estimates. The paper warned a capable machine could derive a private key from an exposed public key in about nine minutes — narrowly within Bitcoin’s 10-minute block window. QSB remains a work in progress. The GPU pinning phase has been successfully tested over roughly six hours across eight Nvidia RTX PRO 6000 GPUs, but the digest search and on-chain broadcast have not yet been completed end-to-end. Transactions also exceed default relay policy limits and must be submitted directly to a miner through services like Marathon’s Slipstream. Levy describes QSB as a last-resort tool, not a replacement for standard usage — but its significance is that the path now demonstrably exists, built from rules already embedded in Bitcoin.
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