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Version: 1.4

Selective Disclosure (SD-JWT)

Holders of verifiable credentials may prefer to keep all the information contained within the credential private from a verifier. Instead, they may opt only to share a specific subset of the properties included in the VC. The identity library implements the IETF Specifications, which outlines a mechanism to enable the selective disclosure of individual properties within the JSON object of JWT claims.

Concept​

Issuance​

During the issuance process, the issuer replaces a subset of the fields in a credential with digests of their salted values and creates a signed JWT. Next, JWT, alongside the plain text disclosures and the salt used for digest creation are sent to the holder.

Presentation​

At this stage, the holder can selectively choose which fields to disclose to the verifier. The disclosures are sent in plain text, with the JWT containing the digests to the verifier.

note

Only values replaced by digests through the issuer can be selectively disclosed. The holder can not conceal values provided in plain text in the JWT claims.

Validation​

With these values and a valid signature, the verifier is able to reconstruct a Verified Credential (VC) that exclusively contains the information the holder intended to disclose.

How It Works​

A SD JWT can be constructed from the following JWT claim of an address credential in accordance with the VC Data Model v1.1:

{
  "iss": "did:iota:tst:0x899d07a766f93c2af1a19a3f4583ad338fc94c5d84b6afcadf49b197e1cb693e",
  "jti": "https://example.com/credentials/3732",
  "nbf": 1705925652,
  "sub": "did:iota:tst:0x6c045e1f658197b432cfc7c66350b8781dca50f820e9de0fcdf0029b4b384355",
  "vc": {
    "@context": "https://www.w3.org/2018/credentials/v1",
    "credentialSubject": {
      "address": {
        "country": "DE",
        "locality": "Maxstadt",
        "postal_code": "12344",
        "street_address": "Weidenstraße 22"
      },
      "name": "Alice"
    },
    "type": [
      "VerifiableCredential",
      "AddressCredential"
    ]
  }
}

The issuer makes the values of "locality", "postal_code", and "street_address" selectively disclosable, giving the holder the freedom to select what details of the address to be disclosed and presented.

{
  "_sd_alg": "sha-256",
  "iss": "did:iota:tst:0x899d07a766f93c2af1a19a3f4583ad338fc94c5d84b6afcadf49b197e1cb693e",
  "jti": "https://example.com/credentials/3732",
  "nbf": 1705925652,
  "sub": "did:iota:tst:0x6c045e1f658197b432cfc7c66350b8781dca50f820e9de0fcdf0029b4b384355",
  "vc": {
    "@context": "https://www.w3.org/2018/credentials/v1",
    "credentialSubject": {
      "address": {
        "_sd": [
          "8Dai0-GMZgkzmdryGzjYufUaRFkiNWzVsJJdWucwu84",
          "jemTNaG_wiHauwmwWiWREsirAlr91qugPds4MA8e2xo",
          "iakC9Dfe2r9fGnOaAr_pGg1b7CwITBjcwE7-O7WlMnY"
        ],
        "country": "DE"
      },
      "name": "Alice"
    },
    "type": [
      "VerifiableCredential",
      "AddressCredential"
    ]
  }
}
note

The digests are contained in the _sd property in address. This allows both keys and values to be concealed.

For further details, see the example below and the sd-jwt-payload crate.

Presentation format​

The SD-JWT is presented in the following format:

<Issuer-signed JWT>~<Disclosure 1>~<Disclosure 2>~...~<Disclosure N>~<optional KB-JWT>

Key Binding JWT​

When a verifier receives an SD-JWT, it may be desirable to verify that the presenter's identity matches the holder of the Credential. For that purpose, a Key Binding JWT (KB-JWT) can be used.

  • The verifier sends a nonce to the holder.
  • The holder creates a JWT containing the nonce and the digest of the issuer-signed JWT and the disclosures 1→N.
  • The holder sends the KB-JWT to the verifier as a part of the presentation.
  • By verifying the KB-JWT, the verifier ensures the identity of the holder, the integrity of the data, the freshness of the signature, and the intended audience.

Full Example Code​

examples/1_advanced/7_sd_jwt.rs
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