Release notes - Cryptography audit chain Ed25519 migration

Sprint: SPRINT_20260501_010_Cryptography_audit_chain_ed25519 Module: Cryptography (src/Cryptography/) Audit finding closed: Pass-2 Group C finding C1 (non-deterministic ECDSA P-256 audit signatures) Status: Pre-prod breaking change. Existing ECDSA-signed audit artifacts, fixtures, and verifier key bundles must be regenerated.

Summary

The Stella audit/evidence signing chain now defaults to EdDSA Ed25519. Evidence capsules, audit bundles, release decision capsules, and attestation evidence must resolve the Ed25519 signer unless a caller explicitly produces a separate regional interop signature.

ECDSA-P256 remains available in the cryptography profile catalog for regional interop, FIPS/eIDAS compatibility work, and profile-specific tests. It is no longer the evidence-chain default because the current P-256 signer is non-deterministic and can produce different signatures for the same canonical payload.

Breaking change

ECDSA-signed audit artifacts produced by previous pre-prod builds will not verify against the new Ed25519 audit/evidence chain. This is deliberate: the migration has no dual-write period, no fallback verifier, and no compatibility shim for the old default.

Operators and test owners must regenerate:

Keep ECDSA fixtures only when the test is explicitly scoped to the EcdsaP256 regional profile. Those fixtures must not be used as proof of the default Stella audit/evidence chain.

Documentation