How Decentralized Identity (DID) Tackles the Challenge of Binding Digital and Real Identities

In the world of Self-Sovereign Identity (SSI), Decentralized Identifiers (DIDs) are a powerful tool that allows individuals to control and manage their digital identity without the need for centralized intermediaries. But one of the most pressing challenges with DIDs is the question of binding: how do we tie a digital identity (a DID) to a real-world individual or entity? Without a reliable binding, anyone could create a DID and falsely claim to be someone they’re not.

Let’s explore the different methods used to ensure that Alice’s DID is truly bound to her real identity, how these mechanisms work, and the technical details behind this critical process.

The Core Issue: Proving the Authenticity of Alice’s DID

In a decentralized world, Alice can create her own DID. This DID is simply a unique string of characters linked to cryptographic keys that she controls. But here's the problem: someone else could create a different DID and claim, “I am Alice too.”

While Alice holds the private key to her DID, the challenge lies in proving that her DID is authentically tied to her real-world identity. Below, we will look at different methods of achieving this binding.

1. Verifiable Credentials as a Trust Anchor

One of the most common ways to bind a DID to a real identity is through Verifiable Credentials (VCs). Verifiable credentials are digital attestations issued by trusted entities, like a government, that can cryptographically assert facts about a person.

Step-by-Step Process:

1. Alice Creates a DID: Alice creates a DID, which is simply a decentralized identifier linked to a public-private key pair. This DID is unique to her, but at this stage, there is no real-world identity attached to it.

The Government Issues a Verifiable Credential (VC): Alice wants to bind her DID to her real-world identity (e.g., her legal name and date of birth). She approaches a trusted issuer, like the government, which also has a DID (did:gov:987654321). After verifying Alice’s identity through a traditional proofing process (in-person verification, for example), the government issues a VC linking Alice’s legal identity to her DID. This VC is digitally signed by the government using its own private key.

The VC might look like this:

{
     "issuer": "did:gov:987654321",
     "credentialSubject": {
        "id": "did:example:123456789abcdefghi",
        "name": "Alice",
        "birthDate": "1990-01-01"
      },

    "proof": {
        "type": "Ed25519Signature2018",
        "created": "2024-10-08T21:00:00Z",
        "proofPurpose": "assertionMethod",
        "verificationMethod": "did:gov:987654321#key-1",
        "jws": "eyJhbGciOiJFZERTQSJ9..."
    }
}        

1. Binding Alice’s DID to Her Identity: In the verifiable credential, the credentialSubject field contains Alice’s DID (did:example:123456789abcdefghi), meaning that this specific DID is tied to Alice’s real-world identity. When the government signs the VC, it creates a cryptographic binding between the real-world identity and Alice’s DID.
2. Verification: Any third party who receives this VC from Alice can verify it by:
3. The cryptographic proof ensures that the VC is valid, hasn’t been tampered with, and binds Alice’s real-world identity to her DID.

2. Web of Trust and Reputation Systems

Another way to bind Alice’s DID to her identity is by relying on webs of trust or reputation systems. Instead of using a single authority (like a government), Alice can obtain endorsements (verifiable credentials) from multiple trusted parties. These endorsements collectively build up a trust profile that strengthens the binding between Alice’s DID and her real-world identity.

Step-by-Step Process:

1. Endorsements from Multiple Trusted Sources: Alice could request verifiable credentials from several trusted entities—such as her employer, her university, or friends who know her. Each of these entities can issue a VC that includes Alice’s DID as the subject, but focuses on different aspects of her identity (e.g., her job title, education, or peer recommendations).
2. Building a Web of Trust: The more trusted parties that endorse Alice’s DID, the stronger the web of trust becomes. Each credential adds a layer of authenticity to Alice’s DID, increasing confidence that the digital identity belongs to the real Alice.
3. Reputation and Verification: When a verifier (like a bank or an online service) interacts with Alice, they can assess her reputation by checking the collection of verifiable credentials linked to her DID. If several reputable entities have endorsed her, the verifier can have confidence that Alice’s DID is truly bound to her identity.

3. Biometric Binding for High Assurance

In some scenarios, biometrics can be used to further strengthen the binding between a DID and a real-world identity. This is particularly useful in high-security environments, where additional assurance is required.

Step-by-Step Process:

1. Biometric Capture: When Alice applies for a digital credential from a trusted entity (such as a government-issued passport), her biometrics—such as a fingerprint or facial scan—are captured during the identity proofing process.
2. Biometrics and Verifiable Credentials: The biometric data is used by the government to verify that Alice is who she claims to be. After successful verification, the government issues a verifiable credential to Alice that includes her DID and attests to her real-world identity.
3. Verification: When Alice presents her VC to a verifier, she can be asked to re-authenticate using biometrics. This additional layer of verification ensures that the person presenting the DID and VC is indeed the same person who was originally verified (Alice). This method is particularly strong because it ties Alice’s physical characteristics (which are hard to replicate) to her DID and digital credentials.

4. DID Resolution and Trust Registries

In decentralized systems, DID resolution and trust registries provide a way to ensure that Alice’s DID is reliably linked to her identity by maintaining records of trusted issuers and verifiable credentials.

Step-by-Step Process:

1. DID Resolution: When Alice shares her DID, a DID resolver can be used to retrieve her DID Document from a decentralized ledger. The DID Document includes Alice’s public key and potentially links to her verifiable credentials, making it possible to validate the authenticity of her DID.
2. Trust Registries: Trust registries are used to store lists of trusted issuers (such as governments, financial institutions, or healthcare providers) that can issue verifiable credentials. If a verifier encounters a credential issued by an entity in a trust registry, they can immediately trust that the credential is legitimate.

5. Selective Disclosure and Privacy-Preserving Methods

Finally, even though the goal is to bind a DID to a real identity, it’s essential to preserve privacy. Using selective disclosure and Zero-Knowledge Proofs (ZKPs), Alice can share only the specific information required by a verifier while keeping other sensitive data private.

For example, Alice can prove that she is over 21 without revealing her birth date. Using ZKP techniques, Alice can demonstrate a fact (e.g., age, location) without exposing any unnecessary details. This preserves her privacy while still proving that her DID is tied to her real identity in a trusted way.

Trust Anchors for Digital Identity Binding

Binding a digital identity to a real-world identity in the decentralized world of DIDs and SSI is challenging but solvable through cryptographic methods and trusted intermediaries. Verifiable credentials, webs of trust, biometric factors, DID resolution systems, and selective disclosure mechanisms all play critical roles in ensuring that a DID can be reliably linked to the person it claims to represent.

In an era of increasing digital interactions, these methods ensure that Alice’s digital identity remains secure, trustworthy, and privacy-preserving, paving the way for a decentralized future where individuals truly control their own identities.