SD-JWT (Selective Disclosure JWT)

SD-JWT is an IETF format that lets a credential holder reveal individual claims from a signed credential without revealing the rest: the issuer signs hashed claim values, and the holder discloses only the claims a given verifier needs, with each disclosure verifiable against the signature. It brings data minimization to credentials, proving age without birthdate, membership without account number.

The mechanism is hashed disclosures. The issuer signs a set of digests rather than the claim values, and the holder supplies the values it chooses to reveal, each of which the verifier hashes and matches against the signature. Undisclosed claims are present as digests that reveal nothing about their contents.

The practical caveat is that selective disclosure limits what a verifier learns, not what it can infer from the combination of what was disclosed and the context it was disclosed in.

The mechanism is hashed disclosures, and understanding it explains both the power and the limits. The issuer signs digests rather than claim values; the holder supplies the values it chooses to reveal; the verifier hashes each and matches it against the signature. Undisclosed claims remain present as digests that say nothing about their contents.

Holder binding is the part that has to be added deliberately. Selective disclosure controls what is revealed and does not by itself prove that the party presenting the credential is its subject rather than someone who obtained a copy, which is why a key-binding proof belongs in the presentation rather than being assumed.

The caveat worth stating to anyone designing a flow is that selective disclosure limits what a verifier learns, not what it can infer. A verifier that sees an age assertion, a request time and a session context may be able to narrow the subject considerably, and the combination of disclosures across several presentations can do more. That is the same linkage problem derived data raises, applied to credentials.

It is a format for presenting a verifiable credential rather than a credential model in its own right.