Ethereum’s post-quantum roadmap puts banks on a 2027 deadline nobody is talking about

Ethereum's post-quantum migration could create a problem for regulated banks years before any quantum computer poses a real threat to validator keys.

Thomas Brunner, Sygnum Bank's Head of Custody and Staking, thinks differently about quantum risk in crypto than most people do.

Ethereum's Post-Quantum team says layer-1 upgrades could be completed by 2029, though it stresses there is no fixed date and the roadmap can still shift. The plan starts with a post-quantum validator-key registry before eventually replacing today's BLS validator signatures with hash-based alternatives such as leanXMSS.

Ethereum shows why bank backups become the danger

BLS is the signature scheme that Ethereum validators use today, and it carries no state to manage, allowing a validator to sign as many times as needed. leanXMSS is built from a structure of one-time keys, and signing twice with the same index hands an attacker the material needed to forge a signature.

NIST's SP 800-208 standard requires stateful hash-based signing to occur within a hardware module, bars the export of private key material, and expects the private key to exist in one instance.

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