Understanding Verifiable Credentials in Blockchain

In the digital era, identity consists of claims made by various authorities. Governments assert citizenship, universities confirm degrees, and employers validate employment. Currently, we rely on physical documents or centralized systems to verify these claims. This approach is inefficient, insecure, and limits user control over personal data.

The Web3 approach addresses these issues through Decentralized Identity (DID), with Verifiable Credentials (VCs) as a fundamental component. VCs provide a standardized, machine-readable format for claims, ensuring security, privacy, and user control. They represent a digital equivalent of passports, driver's licenses, and diplomas, securely stored in crypto wallets.

The Drawbacks of Traditional Credentials

Physical Credentials: Documents such as driver's licenses and passports are prone to loss or theft. Verifying these credentials online is challenging, often forcing individuals to disclose excessive personal information, like showing a full address to prove age.

Digital Credentials (Web2): Identity is often tied to logins with Google, Facebook, or educational institutions. These identities lack portability, and the providers control the data, which they can revoke at any time.

The VC Model: An Alternative Approach

The Verifiable Credential model, standardized by the World Wide Web Consortium (W3C), introduces a decentralized information flow based on a trust triangle.

The Three Roles in the VC Ecosystem:

1. The Issuer: This entity asserts a claim about a subject. Examples include universities issuing degrees, governments providing passports, or events issuing tickets. The issuer cryptographically signs the credential with a private key, creating a tamper-proof digital certificate.

2. The Holder (You): The individual or entity represented by the credential. The holder receives the signed VC from the issuer and stores it in a secure digital wallet, granting them full control over when and with whom to share the credential.

3. The Verifier: An entity that needs to validate a claim about the holder. This could be an employer confirming a degree, a bar checking age, or a DeFi protocol verifying compliance with regulations.

The Workflow:

1. Issuance: A university (issuer) provides a digital diploma (the VC) to a student (holder). The VC is signed and stored in the student’s wallet.

2. Presentation: The student applies for a job and needs to demonstrate they possess a degree. The employer (verifier) requests proof.

3. Verification: The student presents the VC to the employer. The employer's system can:

• Verify the cryptographic signature to ensure authenticity and integrity.
• Confirm the signature corresponds to the public key of the trusted issuer (the university), often by consulting a public registry of Decentralized Identifiers (DIDs).
• Check that the credential has not been revoked by the issuer.

This verification process typically occurs within seconds, without the verifier needing to directly contact the issuer.

The Structure of a Verifiable Credential

A VC is generally formatted as a JSON object (specifically, JSON-LD - Linked Data) with several key components:

Component	Description
@context	Defines the vocabulary used in the VC, referencing standard schemas.
id	A globally unique identifier for the specific credential.
type	The type of credential (e.g., VerifiableCredential, UniversityDegreeCredential).
issuer	The DID of the entity that issued the credential.
issuanceDate	The date when the credential was issued.
credentialSubject	The payload of the credential, detailing the claims made about the subject (e.g., "degree": "Bachelor of Science", "major": "Computer Science"). The subject is identified by their DID.
proof	The issuer’s digital signature, ensuring the credential is tamper-proof. It includes the signature type, creation date, and signature value.

The Power of VCs: Selective Disclosure and Zero-Knowledge Proofs

The effectiveness of VCs significantly increases when combined with Zero-Knowledge Proofs (ZKPs), which enable selective disclosure.

Consider a Verifiable Credential containing your full date of birth. To verify your age to a website:

• Without ZKPs: You must disclose the entire credential, revealing your full date of birth.
• With ZKPs: Your wallet can generate a Zero-Knowledge Proof from the credential. This proof mathematically confirms that the date of birth in the VC, signed by a trusted government issuer, is older than 18 years without revealing the date itself.

The verifier learns only the essential information (that you are over 18) without accessing unnecessary personal data, enhancing privacy significantly.

Use Cases Across Industries

• Education: VCs provide verifiable diplomas and certificates, reducing the risk of forgery.
• Healthcare: Patients can control and share their health records securely.
• DeFi: Individuals can prove accreditation or compliance with KYC regulations without revealing their entire identity.
• DAOs: Permissions and voting rights can be assigned based on verifiable roles or contributions.
• Ticketing: Event tickets can be issued as VCs, ensuring authenticity at entry points.

Barriers to Widespread Adoption

• Interoperability: Ensuring that VCs from one entity can be understood and verified by others requires adherence to universal standards.
• Key Management: The system's security hinges on the holder's ability to manage private keys safely. Improving the user experience related to key management is vital for broader adoption.
• Revocation: Establishing a reliable and standardized mechanism for credential revocation is essential for cases where credentials are lost or issued in error.

Verifiable Credentials serve as a foundational technology for a more user-centric internet. They shift identity control from centralized providers to individuals, allowing claims to be verified while preserving privacy. VCs are critical for creating a secure, trustworthy, and equitable digital future.