IOTA Identity - Credentials

This crate contains types representing verifiable credentials and verifiable presentations as defined in the W3C Verifiable Credentials Data Model.

The IOTA Identity Framework Wiki provides an overview of verifiable credentials and demonstrates how they may be constructed using the building blocks from this crate.

Construction

This crate follows the builder pattern for the creation of Credentials and Presentations.

Example - Credential

Constructing a Credential using the CredentialBuilder.

use identity_credential::credential::Credential;
use identity_credential::credential::CredentialBuilder;
use identity_credential::credential::Subject;
use identity_credential::credential::Issuer;
use identity_core::common::Url;
use identity_core::common::Timestamp;
use serde_json::json;
use serde_json::Value;


// Construct a `Subject` from json
let json_subject: Value = json!({
  "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
  "degree": {
    "type": "BachelorDegree",
    "name": "Bachelor of Science and Arts"
  }
});
let subject: Subject = serde_json::from_value(json_subject).unwrap();

// Construct an `Issuer` from json
let json_issuer: Value = json!({
  "id": "did:example:76e12ec712ebc6f1c221ebfeb1f",
  "name": "Example University"
});

let issuer: Issuer = serde_json::from_value(json_issuer).unwrap();

let credential: Credential = CredentialBuilder::default()
  .context(Url::parse("https://www.w3.org/2018/credentials/examples/v1").unwrap())
  .id(Url::parse("http://example.edu/credentials/3732").unwrap())
  .type_("UniversityDegreeCredential")
  .subject(subject)
  .issuer(issuer)
  .issuance_date(Timestamp::parse("2010-01-01T00:00:00Z").unwrap())
  .build()
  .unwrap();

Important

The generated Credential is not verifiable until it has been signed by the issuer's DID Document.

Example - Presentation

Constructing a Presentation using the PresentationBuilder.

use identity_credential::credential::Credential; 
use identity_credential::presentation::Presentation; 
use identity_credential::presentation::PresentationBuilder; 
use identity_core::common::Url;

// Build a presentation for the given holder and iterator of credentials 
fn build_presentation(credentials: impl Iterator<Item = Credential>, holder: Url) -> Presentation {
  let presentation_builder: PresentationBuilder = PresentationBuilder::default();
  credentials
    .fold(
      presentation_builder,
      |builder: PresentationBuilder, credential: Credential| builder.credential(credential),
    )
    .holder(holder)
    .build()
    .unwrap()
}

Important

A Presentation is not verifiable until signed by the holder's DID Document. All Credentials contained in the presentation must also be signed by their respective issuers.

JSON Serialization

The Credential and Presentation types both implement the Serialize and Deserialize traits from the serde crate. Hence one can use the serde_json crate to obtain Credentials and Presentations from JSON.

Example

Deserializing a Presentation from JSON.

use identity_credential::presentation::Presentation;
use serde_json; 

let presentation_json: &'static str = r#"{
  "@context": "https://www.w3.org/2018/credentials/v1",
  "id": "http://example.org/credentials/3732",
  "type": "VerifiablePresentation",
  "verifiableCredential": [
    {
      "@context": "https://www.w3.org/2018/credentials/v1",
      "id": "https://example.edu/credentials/3732",
      "type": [
        "VerifiableCredential",
        "UniversityDegreeCredential"
      ],
      "credentialSubject": {
        "id": "did:iota:4LCrrVYFQkYYn9VPejhebmMhNnCq24pYPao8yvVLwVje",
        "GPA": "4.0",
        "degree": {
          "name": "Bachelor of Science and Arts",
          "type": "BachelorDegree"
        },
        "name": "Alice"
      },
      "issuer": "did:iota:H3PBNPtLYkVaPpMQVz1R3LeT5zW1Hd6BXQmdtFptaGLR",
      "issuanceDate": "2019-01-01T00:00:00Z",
      "expirationDate": "2024-01-01T00:00:00Z",
      "nonTransferable": true,
      "proof": {
        "type": "JcsEd25519Signature2020",
        "verificationMethod": "did:iota:H3PBNPtLYkVaPpMQVz1R3LeT5zW1Hd6BXQmdtFptaGLR#sign-0",
        "signatureValue": "5H2TSAG3cHnVEt7HZgg6aeYqmzKRQr9BTaP6mgHSE9uH9iLy7pK7TC2A5NHaiiFMGGaY3hJS5WUhfqCW3APxFhSP"
      }
    },
    {
      "@context": "https://www.w3.org/2018/credentials/v1",
      "id": "https://example.edu/credentials/3732",
      "type": [
        "VerifiableCredential",
        "UniversityDegreeCredential"
      ],
      "credentialSubject": {
        "id": "did:iota:b5DtNBzvJfz8jrX1FYYxgvHqvsoFofy1hxzPRMM5iH1",
        "GPA": "4.0",
        "degree": {
          "name": "Bachelor of Science and Arts",
          "type": "BachelorDegree"
        },
        "name": "Alice"
      },
      "issuer": "did:iota:7RD6LT5aSNuKMLJJYorGzhktpTG2TrxGSLmHnWW1Dbb",
      "issuanceDate": "2020-01-01T00:00:00Z",
      "expirationDate": "2023-01-01T00:00:00Z",
      "proof": {
        "type": "JcsEd25519Signature2020",
        "verificationMethod": "did:iota:7RD6LT5aSNuKMLJJYorGzhktpTG2TrxGSLmHnWW1Dbb#sign-0",
        "signatureValue": "4QYkkDLDCZxfa6mymhGTGvG4NRgzdx5Txst7dM6jtfDpBV3Mif8hWH93RzR2MoVCtMgZf3ed7qoZsqepWkp4x9oU"
      }
    }
  ],
  "holder": "did:iota:4LCrrVYFQkYYn9VPejhebmMhNnCq24pYPao8yvVLwVje",
  "proof": {
    "type": "JcsEd25519Signature2020",
    "verificationMethod": "did:iota:4LCrrVYFQkYYn9VPejhebmMhNnCq24pYPao8yvVLwVje#sign-0",
    "signatureValue": "47YLi81cr8atfiyydTe4o989V8GBWZk6rVtvE5bAydhbd8HCK5c3wrNXRbBDAF8PDUBGGGqn8ZjA3jxGDFpQwGAW",
    "challenge": "475a7984-1bb5-4c4c-a56f-822bccd46440"
  }
}
"#;

let presentation: Presentation = serde_json::from_str(presentation_json).unwrap();