DID Peer Method

The DID Peer Method is a Decentralized Identifier (DID) specification defined by the W3C DID Working Group that enables the creation of self-certifying, cryptographically verifiable identifiers for direct, private communication between two or more entities. Unlike ledger-based DID methods (e.g., did:ethr, did:ion), a did:peer is not registered on any public, global blockchain or distributed ledger. Instead, its DID Document is created, exchanged, and stored locally by the peers involved, making it inherently private and suitable for closed ecosystems, offline scenarios, and secure agent-to-agent communication.

The core innovation of the DID Peer Method is its resolution process. A did:peer identifier is generated directly from the DID Document itself using a deterministic algorithm, such as a multibase-encoded hash. This means the DID and its corresponding document are intrinsically linked; possessing one allows you to derive or verify the other. This peer DID is then exchanged out-of-band (e.g., via QR code, NFC, or a secure messaging channel) between parties establishing a connection. The resolution of the DID—translating the did:peer string into its verifiable DID Document—happens entirely locally, without querying an external network.

This architecture provides distinct advantages, including enhanced privacy (no public correlation of interactions), offline usability (no internet required for creation or verification), and low latency (no consensus or network delays). However, it also imposes limitations: peer DIDs are not globally resolvable or discoverable, and they are only meaningful within the context of the specific relationship for which they were created. They are ephemeral by design for single-use contexts or can be made persistent for long-lived connections.

The DID Peer Method is a foundational component for implementing the DIDComm secure messaging protocol and building decentralized, interoperable agent ecosystems, such as those defined by the Hyperledger Aries framework. In these systems, agents generate a unique did:peer for each new relationship, ensuring compartmentalized trust and communication channels. This method is formally specified in the DID Peer Method maintained by the Decentralized Identity Foundation (DIF), ensuring interoperability across different vendor implementations.

In practice, using the DID Peer Method involves a sequence of cryptographic operations. When Alice wants to connect with Bob, her agent generates a DID Document containing her public keys and service endpoints. This document is hashed and encoded to form the did:peer:2 identifier. She sends this DID to Bob via an invitation. Bob's agent can then deterministically reconstruct the expected DID Document from the identifier to verify its authenticity. Once verified, both parties store the peer DID and its document, establishing a trusted, encrypted channel for all future interactions without ever exposing their connection details to a public registry.

The DID Peer Method is a W3C-compliant Decentralized Identifier (DID) method defined by the Decentralized Identity Foundation (DIF) that creates identifiers for direct, ephemeral relationships. Unlike ledger-based methods (e.g., did:ethr, did:ion), a did:peer is generated and exchanged solely between the involved parties, typically during an agent-to-agent protocol like DIDComm. Its core value is enabling offline-first and private identity interactions, as the DID Document is not published to any public verifiable data registry, ensuring the relationship details remain confidential between the peers.

A did:peer is constructed directly from the DID Document itself, creating a self-referential and self-certifying identifier. The standard defines several generation methods, with Method 2 being common for its simplicity: the DID Document's content is encoded (e.g., using Base58BTC) and appended to the did:peer:2 prefix. Because the identifier is derived from the document, any party receiving the DID can instantly reconstruct and verify the associated public keys and service endpoints without querying a resolver. This design eliminates latency, dependency on internet connectivity, and public metadata leakage inherent in blockchain-based lookups.

The primary use case for DID Peer is establishing secure communication channels. When two agents connect, they exchange their did:peer DIDs, which contain the public keys needed for encryption and the service endpoint (e.g., a WebSocket URI) for sending messages. This forms the foundation for the DIDComm v2 messaging protocol. The relationship's context is entirely managed within the agents' wallets or edge agents, making it ideal for mobile applications, IoT device pairing, and any scenario requiring a trusted, direct connection without a public audit trail.

While did:peer identifiers are not intended for long-term, publicly resolvable identity, they are crucial for the peer DID topology in decentralized identity ecosystems. They often serve as the "child" DIDs in a hierarchical relationship, where a long-term, public did:key or did:web acts as a publicly discoverable root. This layered approach combines the benefits of public verifiability for initial discovery with the privacy and efficiency of peer-to-peer interactions for ongoing secure communication, forming a robust architecture for decentralized trust.

The DID Peer method, defined by the Decentralized Identity Foundation (DIF), creates a self-contained, peer-to-peer identifier that does not require resolution on a blockchain or centralized registry. Its syntax follows the W3C DID standard, beginning with the did:peer: method-specific identifier (MSI). The core of a DID Peer is a cryptographically generated, multibase-encoded string derived from the peer's public key and optional routing information, resulting in a complete, portable identifier like did:peer:2.Ez6LSms.... This design enables two parties to establish a direct, verifiable connection by simply exchanging their DID documents.

A DID Peer document is not fetched from a network; it is embedded within the identifier itself or derived deterministically from it. The document structure contains essential verification methods, such as public keys for authentication and key agreement, and service endpoints for communication (e.g., DIDComm messaging). For the did:peer:2 version, the document is generated by decoding the MSI. This approach ensures the identifier and its verification material are intrinsically linked, providing cryptographic certainty and eliminating dependency on external resolution, which is critical for offline or air-gapped scenarios.

The method supports key rotation and peer routing through specific encodings within its syntax. For instance, a DID Peer can encode a list of routing peers, allowing messages to be forwarded through a trusted network. The document's service block is crucial, as it defines the protocols and addresses for secure interactions. Because the entire state is encapsulated, peers can independently verify each other's credentials and communication endpoints without consulting a third party, making DID Peer a foundational protocol for decentralized agent-to-agent communication and secure digital relationships.