Google’s recent paper reveals that Shor’s algorithm can potentially break the cryptography used by Bitcoin and Ethereum with fewer than 500,000 qubits. The paper discloses significant architectural details, suggesting that reproducing similar circuits is feasible for well-resourced quantum research teams. However, the actual hardware needed for an attack remains a substantial barrier.

• Google's paper shows Shor's algorithm could break Bitcoin/Ethereum's 256-bit ECC with under 500,000 physical qubits in about nine minutes—roughly Bitcoin's block time.
• Even though Google withheld exact circuit details, the disclosed architecture (kickmix design, modular inversion, ~2.7 million non-Clifford gates per point addition) gives skilled teams enough to replicate similar circuits within months.
• Goertzel estimates a small expert team could reproduce circuits within 2-3x Google's efficiency in 6-12 months, and even a 2x-worse circuit would still threaten current cryptography.
• The real barrier isn't algorithmic knowledge but building the actual hardware, though well-funded labs or defense contractors could plausibly pursue it.