#Securing Mechanisms in Verifiable Credentials

#Introduction

Securing mechanisms are essential components in the verifiable credentials ecosystem that ensure authenticity and integrity of digital credentials. These mechanisms use cryptography—primarily digital signatures and mathematical proofs—to protect credentials from tampering and enable verification by third parties without requiring direct communication with the original issuer.

Just as a physical passport includes security features like holograms, watermarks, and special inks to prevent forgery, verifiable credentials need digital equivalents to establish trust in an online environment. Securing mechanisms serve as these digital security features, allowing any verifier to confirm that:

1. The credential was issued by the claimed issuer (authenticity)
2. The credential hasn't been altered since issuance (integrity)
3. The credential hasn't been revoked (currency)

Without robust securing mechanisms, verifiable credentials would be vulnerable to forgery, tampering, and replay attacks, undermining the entire trust framework upon which they depend.

#Core Concepts

#Verifiable Credentials and Proofs

A verifiable credential consists of claims (statements about a subject), metadata, and proofs. While the claims and metadata provide the credential's content and context, the proof is what makes the credential verifiable.

The proof component:

• Cryptographically binds the issuer to the credential
• Establishes the credential's integrity
• Enables verification without requiring the verifier to trust intermediaries
• Transforms a regular credential into a verifiable credential

#Trust Model

Securing mechanisms implement a trust model built on these principles:

1. Non-repudiation: Issuers cannot deny having issued properly signed credentials
2. Tamper-evidence: Any modification to a credential invalidates its proof
3. Decentralized verification: Verification doesn't require contacting the issuer
4. Issuer identification: The issuer's identity is cryptographically verifiable
5. Holder empowerment: Holders control presentation of their credentials

This trust model enables the three-party ecosystem of issuers, holders, and verifiers to operate without requiring centralized authorities or continuous connectivity.

#How Securing Mechanisms Work

According to the W3C Data Integrity specification, the creation of cryptographic proofs for verifiable credentials involves three key steps:

#1. Transformation

Transformation prepares the credential data for hashing by converting it into a standardized, deterministic format. This step ensures consistent results regardless of insignificant variations in data representation.

Common transformation methods include:

• Canonicalization: Standardizing the data format (like removing whitespace, ordering properties alphabetically)
• Serialization: Converting complex data structures into a consistent string representation
• Selective transformation: Preparing only specific parts of the credential for protection

The transformation creates what's called "transformed data," which is ready for the hashing process.

#2. Hashing

Hashing applies a cryptographic hash function to the transformed data, creating a fixed-length string that uniquely identifies the content. This hash functions as a digital fingerprint—any change to the input produces a completely different hash value.

Key properties of cryptographic hashes used for verifiable credentials:

• Deterministic: The same input always produces the same hash
• Quick computation: Calculating the hash is computationally efficient
• Pre-image resistance: It's infeasible to derive the original input from the hash
• Collision resistance: It's extremely difficult to find two different inputs with the same hash

Common hash algorithms include SHA-256, SHA-3, and BLAKE2.

#3. Proof Generation

The final step creates a cryptographic proof based on the hash and the issuer's private key. For digital signatures (the most common proof type), this involves encrypting the hash with the issuer's private key to create a signature that can only be verified using the issuer's public key.

This process creates a proof that is:

• Unique to the specific credential
• Bound to the issuer's identity
• Impossible to forge without access to the issuer's private key
• Invalidated by any changes to the credential

#Types of Securing Mechanisms

The W3C specifications define several approaches for securing verifiable credentials:

#Embedded Proofs

Embedded proofs, like those defined in the Verifiable Credential Data Integrity specification, include the proof as a property of the credential itself. The proof contains metadata about the proof method, cryptographic information, and verification details.

{
    "@context": ["https://www.w3.org/ns/credentials/v2", "https://www.w3.org/ns/credentials/examples/v2"],
    "id": "http://university.example/credentials/3732",
    "type": ["VerifiableCredential", "UniversityDegreeCredential"],
    "issuer": "https://university.example/issuers/565049",
    "validFrom": "2010-01-01T19:23:24Z",
    "credentialSubject": {
        "id": "did:example:ebfeb1f712ebc6f1c276e12ec21",
        "degree": {
            "type": "BachelorDegree",
            "name": "Bachelor of Science in Mechanical Engineering"
        }
    },
    "proof": {
        "type": "DataIntegrityProof",
        "cryptosuite": "eddsa-2022",
        "created": "2023-02-24T23:36:38Z",
        "verificationMethod": "https://university.example/issuers/565049#key-1",
        "proofPurpose": "assertionMethod",
        "proofValue": "z58DAdFfa9SkqZMVPxAQpic7ndSayn1PzZs6ZjWp1CktyGesjuTdwQZHZVkm2dLmHkrfYtWd6ZFdCDFG3kXhwrAXR"
    }
}

In this approach, the proof directly attests to the credential content. Verification involves checking the proof against the rest of the credential using the issuer's public key.

#Enveloping Proofs

Enveloping proofs, like those defined in the Securing Verifiable Credentials using JOSE and COSE specification, wrap the entire credential in a cryptographic envelope. The most common implementation uses JSON Web Tokens (JWT) with JSON Web Signatures (JWS).

A JWT consists of three parts:

1. Header: Contains metadata about the token type and cryptographic algorithm
2. Payload: Contains the credential itself
3. Signature: Contains the cryptographic proof

The full JWT is represented as a compact, three-part string separated by periods: header.payload.signature.

#Zero-Knowledge Proofs

Zero-knowledge proofs (ZKPs) allow credential holders to prove possession of valid credentials without revealing the actual credential data. This approach enables selective disclosure and enhanced privacy.

With ZKPs, a holder can prove statements like "I have a valid degree from an accredited university" without revealing which university issued the degree or other details about the credential.

The W3C specifications support various ZKP implementations, including:

• BBS+ signatures
• CL signatures
• SD-JWT (Selective Disclosure JWT)

#Security Considerations

When implementing or using securing mechanisms for verifiable credentials, several key security considerations should be addressed:

#Cryptographic Suite Selection

The choice of cryptographic algorithms and parameters significantly impacts security:

• Algorithm strength: Use only well-established, publicly vetted cryptographic algorithms
• Key length: Select appropriate key lengths based on current security recommendations
• Quantum resistance: Consider the potential future need for quantum-resistant algorithms
• Algorithm agility: Design systems to support algorithm upgrades as needed

Vidos supports various cryptographic suites, allowing you to select the most appropriate approach for your security requirements.

#Key Management

Proper key management is critical for the security of verifiable credentials:

• Private key protection: Secure issuer private keys using hardware security modules or equivalent protections
• Key rotation: Establish policies for periodic key rotation
• Key compromise procedures: Define processes for handling compromised keys
• Verification method documentation: Clearly document how verification keys can be discovered and validated

#Protection Against Attacks

Securing mechanisms must protect against various attack vectors:

• Replay attacks: Prevent credentials from being reused in inappropriate contexts
• Man-in-the-middle attacks: Ensure secure transmission of credentials
• Forgery attempts: Maintain strong cryptographic proof verification
• Revocation bypassing: Implement robust status checking mechanisms

#Privacy Implications

Securing mechanisms have important privacy implications that must be considered in any implementation:

#Balancing Security and Privacy

Different securing mechanisms offer different privacy characteristics:

• Standard digital signatures: Provide strong security but reveal all credential data
• Selective disclosure: Allow revealing only specific attributes while hiding others
• Zero-knowledge proofs: Enable proving properties about credentials without revealing the actual data
• Blinded identifiers: Prevent correlation between different presentations of the same credential

#Signature-Based Correlation

The same digital signature used across multiple presentations can enable correlation:

• Consider using different signing keys for different contexts
• Implement holder binding techniques that prevent unauthorized presentation
• Use pseudonymous identifiers where appropriate

#Integration in Vidos

Vidos provides comprehensive support for verifiable credential securing mechanisms through its service architecture:

#Verifier Service

The Vidos Verifier service validates credentials by:

1. Resolving the issuer's DID to retrieve verification methods
2. Checking the credential's proof against the verification method
3. Verifying the credential hasn't been tampered with
4. Confirming the credential hasn't been revoked

#Configuration Options

Vidos allows configuring security parameters including:

• Acceptable cryptographic suites
• Verification method resolution strategies
• Security level requirements
• Proof validation rules

#Ecosystem Integration

Securing mechanisms interact with other Vidos services:

• Resolver: Retrieves the verification methods needed to validate proofs
• Validator: Checks credential structure and content
• Authorizer: Makes authorization decisions based on verified credentials

#Best Practices

When working with securing mechanisms in the Vidos ecosystem:

1. Use appropriate security levels: Select cryptographic suites based on your threat model
2. Implement key rotation: Periodically rotate cryptographic keys used for signing
3. Verify the entire chain: Validate both the proof and the verification method
4. Consider privacy implications: Choose securing mechanisms that match your privacy requirements
5. Stay current: Update cryptographic implementations as security recommendations evolve

#Conclusion

Securing mechanisms provide the foundation of trust for verifiable credentials by ensuring their authenticity and integrity. Through cryptographic techniques like digital signatures and zero-knowledge proofs, these mechanisms enable the credential ecosystem to function without requiring continuous connectivity or centralized authorities.

Vidos implements a comprehensive approach to securing mechanisms, supporting various proof formats and cryptographic suites while integrating with the broader verification ecosystem. By understanding the principles behind these mechanisms, you can make informed decisions about how to implement and use verifiable credentials securely in your applications.

#References

1. W3C Verifiable Credentials Data Model v2.0
2. W3C Verifiable Credential Data Integrity 1.0
3. Securing Verifiable Credentials using JOSE and COSE