sd-jwt-format

An SD-JWT data format combines an issuer-signed JWT with disclosures containing salts and digests. Selective disclosure is achieved by embedding these digests within the JWT payload, allowing holders to reveal specific claims without exposing the entire credential.

Key binding in SD-JWT+KB works by appending a key binding JWT to the SD-JWT for cryptographic verification. This binding JWT proves that the presenter possesses the private key associated with the credential, preventing unauthorized replay or interception by third parties.

To serialize and issue Verifiable Credentials using SD-JWTs, you generate hashed disclosures for selective claims, embed their digests in the issuer-signed JWT payload, and concatenate the JWT with the serialized disclosure strings.

You need to use salts and digests in JWT payloads when implementing selective claim disclosure. Salts ensure uniqueness and prevent dictionary attacks on the disclosed claims, while digests securely bind the disclosed claim values to the issuer-signed JWT.

Standard JWT libraries can parse the issuer-signed JWT, but SD-JWT requires specific handling for selective disclosure. You must extract digests from the payload, verify them against the provided disclosures with salts, and validate the key binding JWT separately.