Kohaku lead: Quantum-proof Ethereum accounts for $0.07

Nicolas Consigny, lead of the Ethereum Foundation’s Kohaku project, proposed adapting the NIST-standard post-quantum signature SPHINCS+ into a lighter variant called SPHINCS-. In a Saturday post on X he shared a paper that outlines how the change could let accounts add post-quantum protections onchain for roughly $0.07 in gas without a protocol hard fork or a new precompile.

The paper explains that SPHINCS+ can be modified by trimming some parameters to reduce verification computation and storage on Ethereum. That reduction would let users attach a post-quantum verification key to an account, increasing onchain cost only slightly compared with current account operations.

The proposal states the scheme can be adopted by users and smart contracts without changing the Ethereum protocol or adding a precompile, which would allow gradual deployment while researchers work on more efficient post-quantum designs that may require protocol changes.

Consigny described SPHINCS- as “a bridge toward a future post-quantum signature system dubbed ‘leanSPHINCS’,” with leanSPHINCS intended to lower verification costs further by using signature aggregation techniques.

The push for onchain post-quantum protections follows laboratory demonstrations of quantum techniques against small elliptic-curve keys. In April, a researcher using a quantum device extracted a 15-bit elliptic-curve private key from its public key using a variant of Shor’s algorithm. Current quantum hardware remains far from breaking standard 256-bit keys used by many blockchains.

Analytics firm Glassnode estimates about 1.92 million bitcoin are “structurally unsafe” if a quantum attack became feasible, and a further 4.12 million bitcoin are “operationally unsafe” due to key management. Glassnode’s estimates put 13.99 million bitcoin, or about 69.8% of the supply, as not exposed to a quantum threat under current assessments.

The paper frames SPHINCS- as an interim, cost-efficient option that reduces onchain verification costs at some cost to theoretical security margin compared with full SPHINCS+. The proposal presents SPHINCS- as a practical way to begin hardening accounts now while the community evaluates compact, aggregated post-quantum schemes for potential protocol-level adoption.