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 dangerBLS 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.Brunner said that the standard is blunt about the consequen...