Safeguarding cryptocurrency by disclosing quantum vulnerabilities responsibly

Google researchers have presented updated estimates on the quantum computing resources needed to break elliptic curve cryptography used in cryptocurrency systems. The whitepaper describes two quantum circuits implementing Shor's algorithm for the 256-bit elliptic curve discrete logarithm problem. One circuit requires fewer than 1,200 logical qubits and 90 million Toffoli gates while the other uses fewer than 1,450 logical qubits and 70 million Toffoli gates. These circuits are estimated to run on a superconducting qubit cryptographically relevant quantum computer with fewer than 500,000 physical qubits in a few minutes under standard hardware assumptions. This represents an approximately 20-fold reduction compared to previous estimates in the number of physical qubits required. The findings indicate that most blockchain technologies relying on this cryptography face potential future risks from large-scale quantum computers. To disclose these vulnerabilities responsibly, the researchers developed a zero-knowledge proof method that enables third-party verification without providing a detailed roadmap for potential attackers. They engaged with the U.S. government on this approach and encourage other research teams to follow similar practices. The paper also provides recommendations for the cryptocurrency community such as transitioning blockchains to post-quantum cryptography and refraining from exposing or reusing vulnerable wallet addresses. Google has led efforts in the responsible transition to post-quantum cryptography since 2016 and continues work on a 2029 migration timeline. The whitepaper highlights progress toward post-quantum blockchain security and clarifies areas where blockchains remain immune to quantum attacks. The goal is to support the long-term health of the cryptocurrency ecosystem through careful and substantiated disclosure.