Verifiable Credentials

This guide will walk you through what VCs are, how Zetrix supports them, and how to use the Zetrix VC APIs to build decentralized identity and credential systems.

Introduction to Verifiable Credentials

What Are Verifiable Credentials?

Verifiable Credentials (VCs) are digital credentials that are cryptographically secure, privacy-respecting, and machine-verifiable. Based on the W3C VC standard, they are used to represent information such as ID cards, academic degrees, and licenses in a decentralized way.

A VC typically includes:

• Issuer (who issued it)

• Subject (who it's about)

• Claims (the data)

• Proof (digital signature)

Why Use VCs on Zetrix?

• Trustless Verification: No need to call the issuer to validate a VC.

• Data Integrity: Credentials are tamper-evident.

• Privacy-Preserving: Support for selective disclosure with BBS+ signatures.

• Decentralized Identity (DID): Users are identified by unique, blockchain-resolved did:zid identifiers.

High-Level Overview

Roles

• Issuer: Entity that issues a VC.

• Holder: The recipient of the VC.

• Verifier: Entity that checks the authenticity of a VC or Verifiable Presentation (VP).

Credential Lifecycle

1. Template Creation: Issuer defines the schema of the credential.

2. VC Application: Holder requests a VC using a defined template.

3. VC Issuance: Issuer fills in fixed values, signs, and issues the VC.

4. VC Download: Holder downloads the issued VC.

5. VP Creation: Holder creates a Verifiable Presentation.

6. VP Verification: Verifier checks the proof.

7. VC Revocation (optional): Issuer can revoke an issued VC.

System Components

• TDS Smart Contract: Manages on-chain transactions.

• DID Resolver: Resolves did:zid to metadata/public keys.

• Blob Signing: All transactions are submitted as signed blobs.

• Ed25519 + BbsBls: Signature schemes used for W3C compliance and selective disclosure.