8004 Agent Skill v0.0.1

Register AI agents onchain (ERC-8004) and authenticate them via SIWA (Sign In With Agent).

Overview

ERC-8004 ("Trustless Agents") provides three onchain registries deployed as per-chain singletons:

• Identity Registry — ERC-721 NFTs. Each agent gets a unique agentId (tokenId) and an agentURI pointing to a JSON registration file.
• Reputation Registry — Feedback signals (score, tags) from clients to agents.
• Validation Registry — Third-party validator attestations (zkML, TEE, staked re-execution).

SIWA (Sign In With Agent) is a challenge-response authentication protocol (inspired by SIWE / EIP-4361) where an agent proves ownership of an ERC-8004 identity by signing a structured message. See references/siwa-spec.md.

Security Architecture

Full details: references/security-model.md

The agent's private key is the root of its onchain identity. It must be protected against prompt injection, accidental exposure, and file system snooping.

Principle: The private key NEVER enters the agent process

All signing is delegated to a keyring proxy server — a separate process that holds the encrypted private key and exposes only HMAC-authenticated signing endpoints. The agent can request signatures but can never extract the key, even under full compromise (arbitrary code execution via prompt injection).

Agent Process                     Keyring Proxy Server (port 3100)
(auto-detected from               (holds encrypted private key)
 KEYRING_PROXY_URL)

createWallet()
  |
  +--> POST /create-wallet
       + HMAC-SHA256 header  ---> Generates key, encrypts to disk
                              \x3C-- Returns { address } only

signMessage("hello")
  |
  +--> POST /sign-message
       + HMAC-SHA256 header  ---> Validates HMAC + timestamp (30s window)
                                  Loads key, signs, discards key
                              \x3C-- Returns { signature, address }

Why this is secure:

Environment variables:

Auto-detection: When KEYRING_PROXY_URL is set, KEYSTORE_BACKEND automatically defaults to proxy — no need to set it manually. When AGENT_PRIVATE_KEY is set on the proxy server, KEYSTORE_BACKEND defaults to env.

The proxy server stores keys using an AES-encrypted V3 JSON Keystore (scrypt KDF) by default. To use an existing wallet instead, set AGENT_PRIVATE_KEY on the proxy server — the key is held in memory at runtime (no encrypted file needed).

Keystore API

The @buildersgarden/siwa/keystore module exposes ONLY these operations — none return the private key:

createWallet()           → { address, backend }     // Creates key, returns ONLY address
signMessage(msg)         → { signature, address }   // Signs via proxy, key never exposed
signTransaction(tx)      → { signedTx, address }    // Same pattern
signAuthorization(auth)  → SignedAuthorization       // EIP-7702 delegation signing
getAddress()             → string                    // Public address only
hasWallet()              → boolean

getSigner() is not available with the proxy backend — use signMessage() / signTransaction() instead.

IMPORTANT: Install and use the SDK

The agent MUST use the @buildersgarden/siwa SDK to interact with the keyring proxy. The SDK handles HMAC authentication automatically.

Step 1 — Install the SDK (if not already available in your environment):

npm install @buildersgarden/siwa

Step 2 — Set environment variables:

KEYRING_PROXY_URL=https://your-keyring-proxy.up.railway.app
KEYRING_PROXY_SECRET=\x3Cyour-shared-secret>

Step 3 — Use the SDK functions (never call the proxy HTTP endpoints directly):

import { createWallet, signMessage, getAddress } from '@buildersgarden/siwa/keystore';

const info = await createWallet();           // SDK handles HMAC auth internally
const { signature } = await signMessage(msg); // SDK handles HMAC auth internally
const address = await getAddress();           // SDK handles HMAC auth internally

The SDK reads KEYRING_PROXY_URL and KEYRING_PROXY_SECRET from environment variables and constructs the correct HMAC headers automatically.

Fallback: Manual HMAC authentication (without SDK)

If you absolutely cannot install the SDK (e.g. non-Node.js environment, restricted runtime), you can call the proxy HTTP endpoints directly using the HMAC protocol described below. Prefer the SDK whenever possible.

Headers required on every request (except GET /health):

HMAC payload format — a single string with four parts separated by newlines (\ ):

{METHOD}\
{PATH}\
{TIMESTAMP}\
{BODY}

Compute the signature:

HMAC-SHA256(secret, "POST\
/create-wallet\
1738792800000\
{}") → hex digest

Timestamp window: The server rejects requests where the timestamp differs from server time by more than 30 seconds.

Example — create a wallet (Node.js without SDK):

import crypto from 'crypto';

const PROXY_URL = process.env.KEYRING_PROXY_URL;
const SECRET = process.env.KEYRING_PROXY_SECRET;

async function proxyRequest(path: string, body: Record\x3Cstring, unknown> = {}) {
  const bodyStr = JSON.stringify(body);
  const timestamp = Date.now().toString();
  const payload = `POST\
${path}\
${timestamp}\
${bodyStr}`;
  const signature = crypto.createHmac('sha256', SECRET).update(payload).digest('hex');

  const res = await fetch(`${PROXY_URL}${path}`, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'X-Keyring-Timestamp': timestamp,
      'X-Keyring-Signature': signature,
    },
    body: bodyStr,
  });

  if (!res.ok) throw new Error(`${path} failed (${res.status}): ${await res.text()}`);
  return res.json();
}

// Usage
const wallet = await proxyRequest('/create-wallet');        // { address, backend }
const addr = await proxyRequest('/get-address');             // { address }
const sig = await proxyRequest('/sign-message', { message: 'hello' }); // { signature, address }

Example — create a wallet (Python):

import hmac, hashlib, json, time, requests, os

PROXY_URL = os.environ["KEYRING_PROXY_URL"]
SECRET = os.environ["KEYRING_PROXY_SECRET"]

def proxy_request(path, body=None):
    if body is None:
        body = {}
    body_str = json.dumps(body, separators=(",", ":"))
    timestamp = str(int(time.time() * 1000))
    payload = f"POST\
{path}\
{timestamp}\
{body_str}"
    signature = hmac.new(SECRET.encode(), payload.encode(), hashlib.sha256).hexdigest()
    resp = requests.post(
        f"{PROXY_URL}{path}",
        headers={
            "Content-Type": "application/json",
            "X-Keyring-Timestamp": timestamp,
            "X-Keyring-Signature": signature,
        },
        data=body_str,
    )
    resp.raise_for_status()
    return resp.json()

wallet = proxy_request("/create-wallet")       # {"address": "0x...", "backend": "..."}
sig = proxy_request("/sign-message", {"message": "hello"})  # {"signature": "0x...", "address": "0x..."}

Available endpoints:

MEMORY.md: Public Data Only

MEMORY.md stores the agent's public identity state — never the private key:

## Wallet
- **Address**: `0x1234...abcd`       \x3C- public
- **Keystore Backend**: `proxy`      \x3C- which backend holds the key
- **Created At**: `2026-02-04T...`

## Registration
- **Status**: `registered`
- **Agent ID**: `42`
- **Agent Registry**: `eip155:84532:0x8004AA63...`
...

Lifecycle rules:

1. Before any action — Read MEMORY.md. If wallet exists, skip creation. If registered, skip re-registration.
2. After wallet creation — Write address + backend info to MEMORY.md. Private key goes to proxy keystore only.
3. After registration — Write agentId, agentRegistry, agentURI, chainId to MEMORY.md.
4. After SIWA sign-in — Append session token under Sessions.

Template: assets/MEMORY.md.template

Deploying the Keyring Proxy

Before signing anything, the agent needs a running keyring proxy — the separate process that holds the private key and performs all cryptographic operations.

Option A — Railway (Recommended)

Deploy with one click using the Railway template:

This deploys a single keyring-proxy service built from packages/keyring-proxy/Dockerfile. Set these environment variables in Railway:

After deployment, note the proxy URL (e.g. https://your-keyring-proxy.up.railway.app). Set it as KEYRING_PROXY_URL on your agent.

Full deployment guide with architecture details, OpenClaw gateway setup, and verification steps: https://siwa.builders.garden/docs/deploy

Option B — Docker (Self-hosted)

docker build -f packages/keyring-proxy/Dockerfile -t keyring-proxy .
docker run -p 3100:3100 \
  -e KEYRING_PROXY_SECRET=your-secret \
  -e KEYSTORE_PASSWORD=your-password \
  keyring-proxy

Option C — Local Development

cd packages/siwa-testing
pnpm run proxy

Once the proxy is running, set these environment variables on the agent:

KEYRING_PROXY_URL=http://localhost:3100   # or your Railway URL
KEYRING_PROXY_SECRET=your-shared-secret

The proxy keystore backend is auto-detected when KEYRING_PROXY_URL is set — no need to set KEYSTORE_BACKEND manually.

Workflow: SIGN UP (Agent Registration)

Step 0: Check MEMORY.md + Keystore

import { hasWallet } from '@buildersgarden/siwa/keystore';
import { ensureMemoryExists, hasWalletRecord, isRegistered } from '@buildersgarden/siwa/memory';

ensureMemoryExists('./MEMORY.md', './assets/MEMORY.md.template');

if (await hasWallet() && isRegistered('./MEMORY.md')) {
  // Already registered — skip to SIGN IN or update
}
if (await hasWallet() && hasWalletRecord('./MEMORY.md')) {
  // Wallet exists — skip to Step 2
}
// Otherwise proceed to Step 1

Step 1: Create Wallet (key goes to proxy, address goes to MEMORY.md)

import { createWallet } from '@buildersgarden/siwa/keystore';
import { writeMemoryField } from '@buildersgarden/siwa/memory';

const info = await createWallet();  // \x3C- key created in proxy, NEVER returned

// Write ONLY public data to MEMORY.md
writeMemoryField('Address', info.address);
writeMemoryField('Keystore Backend', info.backend);
if (info.keystorePath) writeMemoryField('Keystore Path', info.keystorePath);
writeMemoryField('Created At', new Date().toISOString());

Step 1b: Fund the Wallet (REQUIRED before registration)

STOP — the wallet must have ETH for gas before any onchain transaction can succeed. Registration, URI updates, and metadata changes all require gas fees.

After creating the wallet, you MUST:

1. Show the user the wallet address and the target chain so they can send funds:
   • Address: the value returned by createWallet() or getAddress()
   • Chain: the chain where the agent will register (e.g. Base Sepolia chainId 84532, Base mainnet chainId 8453)
2. Tell the user to send ETH (or the chain's native gas token) to that address on that chain.
3. Wait for the user to confirm they have funded the wallet before proceeding to registration.

For testnets, suggest using a faucet:

• Base Sepolia: Base Sepolia faucet or bridge from ETH Sepolia
• ETH Sepolia: Sepolia faucet

Do NOT attempt to register or send any onchain transaction until the wallet is funded. The transaction will fail with an insufficient funds error.

Example message to show the user:

Wallet created successfully!

  Address: 0x1234...abcd
  Chain:   Base Sepolia (chainId 84532)

Please send some ETH to this address on Base Sepolia to cover gas fees.
You can use a faucet: https://www.alchemy.com/faucets/base-sepolia

Let me know once the wallet is funded and I'll proceed with registration.

Step 2: Build the Registration File

Create a JSON file following the ERC-8004 schema. Use assets/registration-template.json as a starting point.

Required fields: type, name, description, image, services, active.

After building, update MEMORY.md profile:

writeMemoryField('Name', registrationFile.name);
writeMemoryField('Description', registrationFile.description);

Step 3: Upload Metadata

Option A — IPFS (Pinata, recommended):

const res = await fetch('https://api.pinata.cloud/pinning/pinJSONToIPFS', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': `Bearer ${process.env.PINATA_JWT}`
  },
  body: JSON.stringify({ pinataContent: registrationFile })
});
const { IpfsHash } = await res.json();
const agentURI = `ipfs://${IpfsHash}`;

Option B — Base64 data URI:

const encoded = Buffer.from(JSON.stringify(registrationFile)).toString('base64');
const agentURI = `data:application/json;base64,${encoded}`;

Step 4: Register Onchain (signed via proxy)

With the proxy backend, the agent builds the transaction and delegates signing to the proxy:

import { signTransaction, getAddress } from '@buildersgarden/siwa/keystore';
import { writeMemoryField } from '@buildersgarden/siwa/memory';

const provider = new ethers.JsonRpcProvider(process.env.RPC_URL);
const address = await getAddress();

const IDENTITY_REGISTRY_ABI = [
  'function register(string agentURI) external returns (uint256 agentId)',
  'event Registered(uint256 indexed agentId, string agentURI, address indexed owner)'
];

// Build the transaction
const iface = new ethers.Interface(IDENTITY_REGISTRY_ABI);
const data = iface.encodeFunctionData('register', [agentURI]);
const nonce = await provider.getTransactionCount(address);
const feeData = await provider.getFeeData();

const txReq = {
  to: REGISTRY_ADDRESS, data, nonce, chainId,
  type: 2,
  maxFeePerGas: feeData.maxFeePerGas,
  maxPriorityFeePerGas: feeData.maxPriorityFeePerGas,
  gasLimit: (await provider.estimateGas({ to: REGISTRY_ADDRESS, data, from: address })) * 120n / 100n,
};

// Sign via proxy — key never enters this process
const { signedTx } = await signTransaction(txReq);
const txResponse = await provider.broadcastTransaction(signedTx);
const receipt = await txResponse.wait();

// Parse event for agentId
for (const log of receipt.logs) {
  try {
    const parsed = iface.parseLog({ topics: log.topics as string[], data: log.data });
    if (parsed?.name === 'Registered') {
      const agentId = parsed.args.agentId.toString();
      const agentRegistry = `eip155:${chainId}:${REGISTRY_ADDRESS}`;

      // Persist PUBLIC results to MEMORY.md
      writeMemoryField('Status', 'registered');
      writeMemoryField('Agent ID', agentId);
      writeMemoryField('Agent Registry', agentRegistry);
      writeMemoryField('Agent URI', agentURI);
      writeMemoryField('Chain ID', chainId.toString());
      writeMemoryField('Registered At', new Date().toISOString());
    }
  } catch { /* skip non-matching logs */ }
}

See references/contract-addresses.md for deployed addresses per chain.

Alternative: Agent0 SDK

import { SDK } from 'agent0-sdk';
import { readMemory } from '@buildersgarden/siwa/memory';

// Note: Agent0 SDK takes a private key string. If using the SDK,
// you'll need a non-proxy backend or load the key within a narrow scope.
// Prefer the signTransaction() approach above for proxy integration.

Alternative: create-8004-agent CLI

npx create-8004-agent

After npm run register, update MEMORY.md with the output agentId.

Workflow: SIGN IN (SIWA — Sign In With Agent)

Full spec: references/siwa-spec.md

Step 0: Read Public Identity from MEMORY.md

import { readMemory, isRegistered } from '@buildersgarden/siwa/memory';

const memory = readMemory('./MEMORY.md');
if (!isRegistered()) {
  throw new Error('Agent not registered. Run SIGN UP workflow first.');
}

const address = memory['Address'];
const agentId = parseInt(memory['Agent ID']);
const agentRegistry = memory['Agent Registry'];
const chainId = parseInt(memory['Chain ID']);

Step 1: Request Nonce from Server

const nonceRes = await fetch('https://api.targetservice.com/siwa/nonce', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ address, agentId, agentRegistry })
});
const { nonce, issuedAt, expirationTime } = await nonceRes.json();

Step 2: Sign via Proxy (key never exposed)

import { signSIWAMessage } from '@buildersgarden/siwa/siwa';

// signSIWAMessage internally calls keystore.signMessage()
// which delegates to the keyring proxy — the key never enters this process.
const { message, signature } = await signSIWAMessage({
  domain: 'api.targetservice.com',
  address,
  statement: 'Authenticate as a registered ERC-8004 agent.',
  uri: 'https://api.targetservice.com/siwa',
  agentId,
  agentRegistry,
  chainId,
  nonce,
  issuedAt,
  expirationTime
});

Step 3: Submit and Persist Session

import { appendToMemorySection } from '@buildersgarden/siwa/memory';

const verifyRes = await fetch('https://api.targetservice.com/siwa/verify', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ message, signature })
});
const session = await verifyRes.json();

if (session.success) {
  appendToMemorySection('Sessions',
    `- **${agentId}@api.targetservice.com**: \`${session.token}\` (exp: ${expirationTime || 'none'})`
  );
}

SIWA Message Format

{domain} wants you to sign in with your Agent account:
{address}

{statement}

URI: {uri}
Version: 1
Agent ID: {agentId}
Agent Registry: {agentRegistry}
Chain ID: {chainId}
Nonce: {nonce}
Issued At: {issuedAt}
[Expiration Time: {expirationTime}]
[Not Before: {notBefore}]
[Request ID: {requestId}]

Server-Side Verification

The server MUST:

1. Recover signer from signature (EIP-191)
2. Match recovered address to message address
3. Validate domain binding, nonce, time window
4. Call ownerOf(agentId) onchain to confirm signer owns the agent NFT
5. (Optional) Evaluate SIWAVerifyCriteria — activity status, required services, trust models, reputation score
6. Issue session token

verifySIWA() in @buildersgarden/siwa/siwa accepts an optional criteria parameter (6th argument) to enforce requirements after the ownership check:

import { verifySIWA } from '@buildersgarden/siwa/siwa';

const result = await verifySIWA(message, signature, domain, nonceValid, provider, {
  mustBeActive: true,              // agent metadata.active must be true
  requiredServices: ['MCP'],       // ServiceType values from ERC-8004
  requiredTrust: ['reputation'],   // TrustModel values from ERC-8004
  minScore: 0.5,                   // minimum reputation score
  minFeedbackCount: 10,            // minimum feedback count
  reputationRegistryAddress: '0x8004BAa1...9b63',
});

// result.agent contains the full AgentProfile when criteria are provided

See the test server's verifySIWARequest() for a full reference implementation.

MEMORY.md Quick Reference

What is NOT in MEMORY.md: Private keys, keystore passwords, mnemonic phrases.

Reference Files

• references/security-model.md — Threat model, keystore architecture, prompt injection defense
• references/siwa-spec.md — Full SIWA protocol specification (message ABNF, field definitions, security considerations)
• references/contract-addresses.md — Deployed registry addresses per chain, ABI fragments
• references/registration-guide.md — Detailed registration file schema, endpoint types, update flows

Core Library (@buildersgarden/siwa package)

• @buildersgarden/siwa/keystore — Secure key storage abstraction with keyring proxy support
• @buildersgarden/siwa/memory — MEMORY.md read/write helpers (public data only)
• @buildersgarden/siwa/siwa — SIWA message building, signing (via keystore), and server-side verification (with optional criteria)
• @buildersgarden/siwa/registry — Read agent profiles (getAgent) and reputation (getReputation) from on-chain registries. Exports ERC-8004 typed values: ServiceType, TrustModel, ReputationTag
• @buildersgarden/siwa/proxy-auth — HMAC-SHA256 authentication utilities for the keyring proxy

Assets

• assets/MEMORY.md.template — Template for the agent's public identity memory file
• assets/registration-template.json — Starter registration file template