What does the verifier do in SSI, and what can it check?

The verifier requests specific proofs from the holder, receives them as a verifiable presentation, and checks the integrity and authenticity of that presentation.

The flow from the verifier's point of view:

1. Request: it asks the holder for certain proofs ("show me that you are over 18", "show me your driving licence category").
2. Receive: the holder answers with a verifiable presentation, ideally in a reduced, data-minimal form rather than the full credential.
3. Verify:
   • Integrity: the data was not changed since the issuer signed it.
   • Authenticity: it really comes from the claimed issuer (its signature checks out against the issuer's public key from the registry).
   • It also checks that the credential has not expired or been revoked, and that the issuer is one it trusts.

Examples are a shop checking age for alcohol, a car rental checking a licence, or an online service checking identity at sign-up.

Go deeper:

• OpenID for Verifiable Presentations 1.0 — the protocol a verifier uses to request proofs from a wallet.