Seven cents, one signature: Ethereum eyes a 7¢ shield against the quantum apocalypse 🛡️

Ethereum accounts could be retrofitted with post-quantum signature protections for as little as $0.07 per transaction, without waiting for a hard fork, according to Nicolas Consigny, lead of the Ethereum Foundation's Kohaku project. In a Saturday X post, Consigny circulated a paper outlining a leaner way for Ethereum users to guard their accounts against future quantum-computing threats. The approach adapts SPHINCS+, a post-quantum signature standard developed by the US National Institute of Standards and Technology, to work more efficiently on Ethereum. The proposal, dubbed "SPHINCS-," aims to cut onchain verification costs without requiring a protocol change or precompile. Consigny described SPHINCS- as a bridge toward a future post-quantum signature system called "leanSPHINCS," which would further reduce verification costs through aggregation. The paper seeks to mitigate the long-term risk quantum computing poses to Ethereum's Elliptic Curve Digital Signature Algorithm at a price point that could make deployment viable before any dedicated hard fork is developed.

The broader quantum threat has gained attention across the crypto industry. In April, post-quantum startup Project Eleven awarded a prize to researcher Giancarlo Lelli for using a quantum computer to break a 15-bit elliptic-curve key. Bitcoin's keys are 256 bits long, considerably larger than the 15-bit key Lelli managed to crack. He derived the private key from its paired public key using a variant of Shor's algorithm, a quantum-computing technique that theoretically threatens the cryptography used by Bitcoin ($BTC).

According to Glassnode, roughly 1.92 million Bitcoin, nearly 10% of the total supply, are considered "structurally unsafe" in a future quantum-attack scenario. A further 4.12 million BTC, or 20.6% of supply, are classified as "operationally unsafe" due to key or address management practices. Glassnode estimates the remaining 69.8% of supply, or 13.99 million Bitcoin, remains unexposed to a quantum-computing threat, broadly consistent with Ark Invest's March estimate that 65% of the supply was safe. The Kohaku proposal, if adopted, would give Ethereum ($ETH) users a low-cost opt-in path while longer-term post-quantum standards continue to be researched.