DID Namespace

A DID Namespace is the method-specific prefix in a Decentralized Identifier (DID), defined by the did: scheme and a unique method name. It follows the format did:<method-name>:. This namespace is a critical part of the DID syntax, did:<method>:<method-specific-identifier>, and serves as a routing mechanism. It tells a DID resolver which DID method specification to use to interact with the underlying blockchain or ledger where the DID's cryptographic keys and service endpoints are anchored. For example, the namespace did:ethr: indicates the DID is managed via the Ethereum blockchain using the ethr method specification.

The primary function of a DID namespace is to ensure global uniqueness and interoperability across different decentralized systems. Each namespace is registered in the W3C DID Specification Registries, which maintains a controlled list of approved method names. This prevents collisions where two different methods might use the same identifier string. The namespace decouples the identifier from any single vendor, network, or technology, enabling a user's DID to be portable and verifiable across various platforms as long as they support the specified method. It is the key that unlocks the correct protocol for DID resolution and DID document retrieval.

From a developer's perspective, the namespace dictates the technical requirements for implementing a DID. A did:key: namespace implies a simple, self-contained DID, while did:ion: (ION, based on Bitcoin) or did:web: (hosted on a web domain) involve more complex resolution logic and trust models. When building applications, correctly interpreting the namespace is the first step in determining how to authenticate a user, verify a signature, or discover linked services. The namespace system creates a modular, extensible identity layer for the decentralized web, allowing new verification methods to emerge without disrupting existing identifiers.

A DID Namespace is the first component of a Decentralized Identifier (DID), specifically the segment before the colon (:), which defines the DID method and its governing system. For example, in the DID did:ethr:0xab..., the namespace is ethr. This prefix acts as a routing mechanism, instructing a DID resolver which specific set of rules, or DID method specification, to use for creating, reading, updating, and deactivating the DID document. It ensures that identifiers from different ecosystems, like did:web, did:key, and did:ion, remain globally unique and interoperable by segregating them into distinct, method-specific domains.

The primary function of a namespace is to enable discovery and resolution. When a system encounters a DID, it parses the namespace to select the correct resolver library or network driver. This resolver then interacts with the appropriate verifiable data registry—such as a blockchain, distributed ledger, or decentralized file system—to fetch the associated DID Document. This document contains the public keys, service endpoints, and authentication protocols necessary to interact with the identity. Without a standardized namespace, resolvers would have no deterministic way to locate the correct verification logic across the internet's fragmented systems.

Namespaces are formally registered in the W3C DID Specification Registries to prevent collisions and promote interoperability. A registered namespace guarantees that the associated DID method has a publicly documented specification. This registry is crucial for developers building wallets, verifiers, and other identity tools, as it provides a trusted reference for supported methods. It transforms the decentralized identity landscape from a chaotic set of incompatible systems into a coherent, addressable network where any entity can be uniquely and verifiably referenced, regardless of the underlying technology stack.

A DID namespace is the unique identifier prefix that specifies the DID method to be used for creating, reading, updating, and deactivating a DID. It follows the did: scheme and precedes the method-specific identifier, as in did:example:123456. This namespace is formally registered in the W3C's DID Specification Registries, ensuring global uniqueness and preventing collisions between different method implementations. Registration involves submitting a detailed specification that defines the method's operations, security properties, and governance model.

The syntax for a complete DID is defined as: did:<method-name>:<method-specific-identifier>. The method-name is a lowercase string that constitutes the namespace, such as key, ethr, or web. This segment is crucial for resolvers and other systems to know which DID method driver to invoke for interacting with the identifier. The method-specific identifier is a string generated and interpreted according to the rules of that particular namespace, often derived from a public key, a blockchain address, or a database record.

Registering a namespace is a formal process that promotes interoperability and trust. Proposers must document the method's CRUD operations (Create, Read, Update, Deactivate), its verification methods (like public keys), and its security considerations. This public registration allows developers to discover and reliably implement support for the method. It transforms a proprietary identifier system into a standardized, web-scale component, enabling verifiable credentials and decentralized applications to function across different ecosystems without central coordination.