What are OpenID4VCI and OpenID4VP used for in an SSI ecosystem?

OpenID4VCI is the protocol by which a wallet obtains (is issued) a verifiable credential from an issuer; OpenID4VP is the protocol by which a verifier requests and receives a verifiable presentation from a wallet.

Both extend the OpenID / OAuth 2.0 family that many services already run, which is why they were chosen for the Swiss E-ID:

• OpenID4VCI (Verifiable Credential Issuance): the issuer acts like an OAuth authorisation server; the wallet goes through an OAuth-style flow and receives the credential, bound to a key held by the wallet.
• OpenID4VP (Verifiable Presentations): the verifier sends a request describing which credentials and claims it wants (for example via a QR code); the wallet shows the request to the holder and, with consent, returns a presentation.

They define the transport between the parties; the credential format inside (here SD-JWT) is a separate choice. Reusing a familiar protocol family lowers the entry barrier for relying parties, one of the SSI challenges.

Go deeper:

• OpenID for Verifiable Credential Issuance 1.0 — the issuance protocol.
• OpenID for Verifiable Presentations 1.0 — the presentation protocol.