What is a Decentralized Identifier (DID)?

DIDs are identifiers that enable verifiable, decentralized digital identities. A DID refers to any subject (e.g. a person, group, organization, abstract entity, etc.) as determined by the controller of the DID. Specifically, DIDs are URIs (unique digital addresses) that associate a DID subject with a DID document allowing trustable interactions associated with that subject. Similar to a URL, when you resolve a DID, you receive a DID document in JSON, JSON-LD, or similar format.

A simple DID example

A DID is a simple unique text string consisting of three parts:

1. the did URI scheme identifier;
2. the identifier for the DID method; and
3. the DID method-specific identifier.

The example DID above resolves to a DID document.

Multiple DIDs

A subject may have as many DIDs as they want for different use cases, such as:

• a DID for educational certificates; or
• a DID for verified identity / KYC documents; or
• a DID for online gaming accounts.

What is a DID Document?

A DID document contains information associated with the DID, such as ways to cryptographically authenticate a DID controller.

{
  "@context": [
    "https://www.w3.org/ns/did/v1",
    "https://w3id.org/security/suites/ed25519-2020/v1"
  ],
  "id": "did:example:123456789abcdefghi",
  "authentication": [{
    "id": "did:example:123456789abcdefghi#keys-1",
    "type": "Ed25519VerificationKey2020",
    "controller": "did:example:123456789abcdefghi",
    "publicKeyMultibase": "zH3C2AVvLMv6gmMNam3uVAjZpfkcJCwDwnZn6z3wXmqPV"
  }]
}

DID Methods

A DID method (and its spec) defines the precise operations by which DIDs and DID documents are created, resolved, updated, and deactivated. There are currently more than 150 DID methods out there, which can be categorized into 4 main types based on their storage method:

• Centralized: relies on a Web2 server
• Blockchain-based: the “original” DID method involving a blockchain
• Hybrid: uses decentralized storage to store its documents
• Static: no data registry is required; can be created and resolved by encoding/decoding data directly.

Terminal 3 currently provides a custom did:t3n DID.

DID System Architecture

Generic DID Architecture