DIDComm

DIDComm encrypts messages at the application layer using Authenticated Encryption with Associated Data (AEAD), ensuring confidentiality and integrity regardless of the transport mechanism. Each message is encrypted for a specific recipient's public key, derived from their Decentralized Identifier (DID). This means even if the underlying transport (HTTP, Bluetooth, etc.) is compromised, the message content remains opaque.

• Uses ECDH-ES key agreement for per-message encryption
• Supports both anoncrypt (anonymous encryption) and authcrypt (authenticated encryption) modes
• Provides perfect forward secrecy when ephemeral keys are used

DIDComm relies on DID Documents—JSON-LD files stored on distributed ledgers or decentralized networks—to resolve public keys and service endpoints. There is no central certificate authority. Agents discover each other's cryptographic material by resolving DIDs, enabling trustless communication without pre-shared keys or federated identity providers.

• DIDs are self-sovereign: the owner controls the private keys
• Supports multiple DID methods (did:web, did:key, did:indy, did:cheqd)
• Enables interoperability across different identity networks

DIDComm messages are designed to be transport-independent. The protocol defines a message structure and encryption envelope that can be transmitted over HTTP, WebSockets, Bluetooth, NFC, or even push notifications. This makes it ideal for agent mesh networks where agents communicate across heterogeneous environments—from cloud servers to edge devices.

• DIDComm V2 standardizes message format in JSON
• Supports routing protocols for store-and-forward delivery
• Enables offline-first communication patterns via mediators

DIDComm establishes secure sessions using Diffie-Hellman key agreement over elliptic curves (X25519). The protocol performs a handshake where both parties derive a shared secret from their DID keys, authenticating each other in the process. This shared secret then derives symmetric keys for subsequent message encryption.

• Uses Curve25519 for key exchange
• Supports multi-recipient messages via key wrapping
• Prevents man-in-the-middle attacks through DID-based authentication

DIDComm defines a routing protocol that allows messages to traverse intermediary agents (mediators) to reach recipients that are offline or behind NATs. Mediators store encrypted messages and forward them when the recipient connects. This is critical for mobile agents and edge devices that cannot maintain persistent connections.

• Forward secrecy is preserved: mediators cannot decrypt payloads
• Supports relay and store-and-forward mediator roles
• Enables asynchronous communication patterns

DIDComm messages carry a protocol identifier and message type that allow agents to co-execute structured interactions. Beyond simple messaging, agents can negotiate credentials, issue Verifiable Credentials (VCs), or coordinate multi-step workflows. Each protocol defines a state machine that both parties follow.

• Built-in protocols for trust ping, discover features, and issue credential
• Extensible: developers define custom protocol URIs
• Enables rich, stateful agent interactions beyond fire-and-forget messaging

A JSON-LD document associated with a DID that contains the cryptographic material and service endpoints required to initiate secure communication. When an agent resolves a DID, it retrieves this document to discover how to encrypt messages and where to deliver them.

• Lists verification methods (public keys) for authentication
• Declares service endpoints for message delivery (HTTP, WebSocket, etc.)
• Supports key rotation through versioned updates on the registry

Authenticated Encryption with Associated Data is the cryptographic primitive securing every DIDComm message envelope. It simultaneously provides confidentiality, integrity, and authenticity for the message payload while binding it to unencrypted context headers.

• Prevents tampering with routing metadata
• Ensures only the intended recipient can decrypt the content
• Uses algorithms like XChaCha20-Poly1305 or AES-GCM

A security property ensuring that the compromise of a long-term private key does not compromise past session keys. DIDComm implementations leverage ephemeral key exchanges through the Noise protocol to guarantee that each message exchange is protected independently.

• Limits the blast radius of any single key compromise
• Achieved through ephemeral Diffie-Hellman key agreement per session
• Essential for long-lived agent relationships with rotating keys