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Overview

ACK-ID is a protocol built on W3C Standards designed to bring verifiable, secure, compliant identity, reputation, and service discovery to agents. A2A (Agent2Agent) is a protocol developed by Google to standardize communication between multiple agents. This interactive command-line demo showcases how two A2A-compatible agents can use ACK-ID to verify each other’s identity and trust that they are communicating with the expected agent.

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Getting Started

Before running this demo, follow the Quickstart Guide to ensure you are set up properly.

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Running the Demo

You can use the demo by running the following command from the root of this repository: 
pnpm run demo:identity-a2a
Alternatively, from within the demo directory (./demos/identity-a2a): 
pnpm run demo

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Demo Walkthrough

This demo showcases a mutual authentication flow between a Bank Customer Agent and a Bank Teller Agent using ACK-ID DIDs and JWTs exchanged within A2A message bodies. The demo walks through the following authentication flow:
1

Initial Contact - Customer Agent Initiates

The Customer Agent sends an authentication request as an A2A message containing a signed JWT with a nonce:
{
  "role": "user",
  "kind": "message",
  "messageId": "f1f54f9d-6db2-4d78-8b38-4e50d77c8b19",
  "parts": [
    {
      "type": "data",
      "data": {
        "jwt": "<signed-JWT-from-customer>"
      }
    }
  ]
}
The JWT payload includes:
{
  "iss": "did:web:customer.example.com",
  "aud": "did:web:bank.example.com",
  "nonce": "c-128bit-random",
  "iat": 1718476800,
  "jti": "0e94d7ec-...",
  "exp": 1718477100
}
2

Bank Teller Agent Response

The Bank Teller Agent verifies the customer’s JWT signature and responds with its own signed JWT, including both the customer’s nonce and a new server nonce:
{
  "role": "agent",
  "kind": "message",
  "messageId": "f1f54f9d-6db2-4d78-8b38-4e50d77c8b19",
  "parts": [
    {
      "type": "data",
      "data": {
        "jwt": "<signed-JWT-from-bank>"
      }
    }
  ]
}
The Bank’s JWT payload:
{
  "iss": "did:web:bank.example.com",
  "aud": "did:web:customer.example.com",
  "nonce": "c-128bit-random",
  "replyNonce": "b-128bit-random",
  "jti": "1f85c8fa-...",
  "iat": 1718476805,
  "exp": 1718477105
}
3

Subsequent Communications

After successful mutual authentication, all subsequent messages include a signature in the metadata:
{
  "role": "user",
  "kind": "message",
  "messageId": "89f2e11b-5b0a-4c3b-b49d-14628e5d30fb",
  "parts": [
    {
      "type": "text",
      "text": "Please check the balance for account #12345"
    }
  ],
  "metadata": {
    "sig": "eyJhbGciOiJFZERTQSIsInR5cCI6IkpXVCJ9...Q"
  }
}
The signature is a JWT with the payload:
{
  "message": <the-message-object-without-metadata>
}
with aud and iss set for the counterparty and sender’s DID, respectively.

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Security Benefits

This authentication flow provides several security advantages:
  • Mutual Authentication: Both parties prove their identity through cryptographic signatures.
  • Replay Attack Prevention: Nonces and JWT IDs ensure messages cannot be replayed.
  • Man-in-the-Middle (MITM) Protection: The aud and iss fields are pinned in the JWTs, preventing tampering. An attacker cannot modify requests or responses without invalidating the signatures.
  • Short-lived Tokens: 5-minute expiry limits the window for potential attacks.
  • Verifiable Identity: DID-based authentication ensures cryptographic proof of identity.

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Further Exploration