Registries

Registries answer the question a signature cannot: not "is this credential intact?" but "should I trust whoever signed it?"

Registry	Says
Trusted lists	Which issuers a member state vouches for
Relying party registers	Which verifiers exist and what each declared it will ask for
Wallet provider lists	Which wallet implementations are certified
Rulebooks and catalogues	What a credential type means and which claims it carries

Why verifiers are registered too

A wallet should not release attributes to an unknown party. Registration makes the verifier's identity and its declared purpose checkable at the moment of the request — the holder sees who is asking and what they said they need it for.

The trust chain

A credential is signed by a key, the key is certified by an authority, and the authority appears on a published list. Verification walks that chain to a root the verifier already trusts.