Decentralized Trust Graph (DTG) Credentials

NOTE: This is an early implementation to v0.3 of these specifications.

See the First Person Project Whitepaper for more information.

This library supports both W3C VC 1.1 and 2.0 specifications.

See CHANGELOG.md for release history.

Credential Type Hierarchy

All credentials inherit from the abstract DTGCredential.

VerifiableCredential
└── DTGCredential
    ├── MembershipCredential (VMC)
    ├── RelationshipCredential (VRC)
    ├── InvitationCredential (VIC)
    ├── PersonaCredential (VPC)
    ├── EndorsementCredential (VEC)
    ├── WitnessCredential (VWC)
    └── RelationshipCard (RCard) [VDS - not a credential]

End to End Example

An end-to-end example of creating, signing and verifying a DTG Credential exists in examples

cargo run --example sign_and_verify

Creating credentials

Each credential type has it's own new_*() function to create a new credential of that type.

Example:

let vpc = DTGCredential::new_vpc(issuer, subject, valid_from, valid_to);

The created DTGCredential can be serialized to JSON using serde_json allowing it to be passed into various signing libraries

Signing credentials

By default the affinidi-signing feature is enabled which allows you to sign a credential

let mut vpc = DTGCredential::new_vpc(issuer, subject, valid_from, valid_to);

vpc.sign(&signing_key).await?;

Verifying credentials

There are two ways to validate a credential:

Method 1: If you have the public key bytes that correspond to the signing key, then you can directly verify the credential:

let signing_key = Secret::generate_ed25519(None, None);
let mut vpc = DTGCredential::new_vpc(issuer, subject, valid_from, valid_to);

vpc.sign(&signing_key).await?;

vpc.verify(&signing_key.get_public_bytes())?;

Method 2: If you do not have the public key material, you are likely going to need to resolve the DID VerificationMethod and derive the public key bytes used when creating the credential.

let mut credential = serde_json::from_str(<raw_credential_string>);

// Get the proof
let proof = if let Some(proof) = &credential.credential().proof {
  proof.clone()
} else {
    bail!("credential is not signed!");
};

// Strip proof from the credential
let unsigned = DTGCommon {
  proof: None,
  ..credential.credential().clone()
};

tdk.verify_data(&unsigned, None, &proof).await?;

Common functions

You can deal with the raw credential as required.

let vrc = DTGCredential::new_vrc(issuer, subject, valid_from, valid_to);

let credential = vrc.credential();

You can determine the credential type easily using:

let vmc = DTGCredential::new_vmc(issuer, subject, valid_from, valid_to);

if let DTGCredentialType::VMC = vmc.type_() {
  // Good
}

Has this Credential been signed?

let vmc = DTGCredential::new_vmc(issuer, subject, valid_from, valid_to);

if vmc.signed() {
  println!("Credential has been signed");
} else {
  println!("Credential has not been signed");
}