ADR-008 — Signing curve

Status: Accepted.

Context

Ed25519 is not supported at standard tier by AWS KMS or Azure Managed HSM, and regulated counterparties care about FIPS validation.

Decision

ECDSA P-256 (ES256) is the mandatory-to-implement baseline — FIPS 140-3 validated, supported everywhere, credible with a general counsel. The spec is curve-agnostic via the alg header, so post-quantum migration is a header change, not a redesign.

Consequences