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0.2.2 • Public • Published

Identity Agent

The Identity Agent is a Self-Sovereign Identity agent based on DIDs.

The Agent is capable of communicating with other DID-based agents using end-to-end encryption, as well as requesting and resolving Verifiable Credentials.

The Agent can be run via the command line, in the browser or on a remote server, and is designed to be extensible to support various use-cases and environments.


  • Resolve a DID to a document with a pluggable DID resolver
  • Sign, encrypt, decrypt and verify a message using DIDs
  • Send a message E2E encrypted using a simple decentralized 'hub' API
  • Create and process long-running tasks for credential presentation

TODO for V1

  • Integrate with a remote DID resolver (e.g uniresolver.io)
  • A simple local credential store and presentation resolver
  • Resolve tasks on incoming messages

Quick Start

Running as a library

yarn add @identity.com/identity-agent
const did = 'did:your-did-here'
const agent = await Agent.for(did).build()

const bob = 'did:bobs-did'
await agent.send({ message: 'hello Bob!'}, bob)

Building locally

Note: Before contributing to this project, please check out the code of conduct and contributing guidelines. Thanks!


Identity-Agent uses nvm and yarn

nvm i

Start a REPL like this:

yarn repl

Agent creation

Register a DID


Create a privileged agent

Creating an agent with a private key

a = await Agent.for(Alice.did).withKeys(Alice.signingKey, Alice.encryptionKey).build()

// shorter version
a = await Agent.for(Alice).build()

Create a non-privileged agent

Creating an agent with no private keys (e.g. a mediator or relay)

b = await Agent.for(Bob.did).build()


Send a message via HTTP

message = { hello: 'Bob' }
await a.send(message, Bob.did)

Sign a message

jwt = await a.sign({some: 'payload'})

Verify a message

verifiedPayload = await b.verify(jwt)

Subject operations

Resolve a verifiable presentation

presentation = {} // dummy

taskContext = a.asSubject().resolvePresentationRequest(presentation, Bob.did)

await taskContext.waitForDone()

Verifier operations

Request a verifiable presentation

request = {}

taskContext = a.asVerifier().requestPresentation(request, Bob.did)

await taskContext.waitForDone()

Running the example browser app

The example app must be linked to the library using yarn link.

yarn link
cd examples/browser
yarn link identity-agent
yarn start


Given the variety of identity use-cases, the Identity Agent is designed to be flexible. However, it does have some core concepts and design patterns that are described in this document.

Extending the Agent

The Agent uses dependency injection to allow it to be extensible by clients.

The following example shows how to inject an alternative storage module, e.g. to store messages in a database:

import { AgentStorage } from 'identity-agent';

class MyDBStorage implements AgentStorage {
  // ...implement the interface

const myDBStorage = new MyDBStorage()
Agent.for(did).with<AgentStorage>(TYPES.AgentStorage, myDBStorage)


The following components are used by the Identity Agent:

Module Description Default
AgentStorage Storage interface used to store and retrieve DID documents and task state Backed by node-localstorage.
Stores data in localstorage when run in the browser,
and in a scratch folder when run via node.
DIDResolver A function which resolves a DID to its document Looks up an AWS S3 bucket, if credentials are provided,
otherwise uses a local in-memory cache. Note - retrieved DID
documents are stored in the AgentStorage.
CryptoModule Encapsulates cryptographic functions such as encrypting, decrypting and signing Uses tweetnacl and the X25519 curve for encryption/decryption
and bitcoin-js and the Secp256k1 Bitcoin curve for signing.
Transport An interface uses for communicating with other agents (including remote agents
controlled by the same DID)
Backed by the Http module
Http A Http client Backed by node-fetch (uses window.fetch on the browser)
IssuerProxy A client-side proxy for credential issuers. Used by the identity agent to make
credential requests.
A stub. This should be replaced by clients. An identity.com
IDV Toolkit proxy is under development.
PresentationVerification A service that cryptographically verifies presented credentials A stub. The implementation depends on the type of credentials
and proofs used. An identity.com-compliant implementation is
under development.
Presenter A service that locates and presents credentials in response to a presentation
A stub. An identity.com-compliant implementation is
under development.


Tasks are defined as:

  • long-running
  • resumable
  • interactive
  • chainable


Examples are:

  • PresentationRequest: a verifier requests a presentation from a subject:
  • Presentation: a subject receives a presentation request from a verifier and responds with a presentation of one or more credentials.
  • CredentialRequest: a subject requests the issuance of a credential from an issuer. This usually results in a flow of information from the subject to the issuer as they validate the subject's identity.


If a process may take longer than 1-2 seconds, it may make sense to model it as a task. The reason for this is resumability (see below).


Since agents are often used on mobile devices, browsers, or are otherwise ephemeral, long-running tasks must be able to store and resume their own state, so that they can continue after the agent has restarted.

For example, a credential request task may be in progress with an issuer, that is performing background checks that may take days. Once complete, the credential request task should be completed, resulting in a credential stored in the AgentStorage.


Tasks may require input from the user or some external service. For example, a credential request may require the user to answer questions from the issuer, or a remote agent may require permission from the user before presenting a credential to a verifier.


Tasks may spawn or resolve other tasks. Consider thee following complicated but plausible example.

  • Potential employer E, asks candidate C for their university transcript (PresentationRequest Task 1)
  • C does not recognise E and asks for their "Organisation Credential" (PresentationRequest Task 2)
  • E requests an organisation credential from an issuer I1 capable of issuing such credentials (CredentialRequest Task 3)
  • I1 issues a credential to E, resolving task 3
  • E sends the credential to C, resolving task 2
  • C accepts the credential, and asks their university U to issue them with a transcript credential (PresentationRequest Task 4)
  • In order to verify they are speaking to the correct former student, U asks C to provide their passport credential (CredentialRequest Task 5)
  • C scans and sends their passport document to U as a self-signed credential, resolving task 5.
  • U accepts the self-signed credential as sufficient proof and issues the transcript credential, resolving task 6
  • Finally, C presents the transcript credential to E, resolving task 1

Task Architecture

Tasks are designed using the CQRS model and Event Sourcing, so that state can easily be stored and rehydrated when an agent is resumed.

Tasks are therefore not directly manipulated, but are updated by executing commands, which emit events. The task state is the composition of the payloads of each of these events.

Events can themselves trigger new commands, so the entire task can be modelled as a flow.

Formally a flow consists of the following:

  1. A State type: this defines the contents of the task. Each event payload is therefore a deep subset of this state.
  2. A set of command types
  3. A set of event types
  4. A set of default Command Handlers that are executed when a command is triggered
  5. A set of default Event Handlers that are called when an event of a particular type is added to the task.


By default, an agent is in neutral role, i.e. it has not assumed a role in the SSI trust triangle.

In order to keep the base API simple, most actions that an agent can perform are hidden behind the role APIs: Subject and Verifier.

To switch role, call the following functions:






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