Claude Signs Messages: ERC-8128 MCP Tools for Verifiable AI Communications

2026-06-13

Claude desktop agents can now create verifiable digital signatures through MCP tools, enabling trusted AI communications that prove message authenticity onchain. The ERC-8128 standard provides a framework for AI agents to sign HTTP requests and messages with cryptographic proof, and WAIaaS implements this as native MCP tools that integrate directly with Claude's workflow.

Why Message Signing Matters for AI Agents

When AI agents interact with external services or make financial decisions, proving the authenticity of their communications becomes critical. Traditional API keys can be stolen or spoofed, but cryptographic signatures tied to blockchain addresses provide unforgeable proof of origin. This enables use cases like verified AI-to-AI transactions, auditable agent decisions, and trusted cross-platform communications.

ERC-8128 standardizes this process by defining how AI agents should sign HTTP requests and arbitrary messages, creating a verifiable trail of agent actions that can be validated onchain or offchain.

ERC-8128 MCP Tools in WAIaaS

WAIaaS provides 2 dedicated MCP tools for ERC-8128 message signing as part of its 45 MCP tools for AI agent integration. These tools allow Claude to create and verify cryptographic signatures without requiring deep knowledge of wallet management or cryptographic operations.

Here's how to set up Claude with ERC-8128 signing capabilities:

{
  "mcpServers": {
    "waiaas": {
      "command": "npx",
      "args": ["-y", "@waiaas/mcp"],
      "env": {
        "WAIAAS_BASE_URL": "http://127.0.0.1:3100",
        "WAIAAS_SESSION_TOKEN": "wai_sess_<your-token>",
        "WAIAAS_DATA_DIR": "~/.waiaas"
      }
    }
  }
}

Once configured, Claude gains access to the erc8128-sign-request and erc8128-verify-signature tools. Here's what these tools enable:

Signing HTTP Requests with ERC-8128

The erc8128-sign-request tool allows Claude to create cryptographically signed HTTP requests. This is particularly useful when the agent needs to prove its identity to external services:

# Claude can sign an HTTP request to prove authenticity
curl -X POST http://127.0.0.1:3100/v1/tools/erc8128-sign-request \
  -H "Authorization: Bearer wai_sess_<token>" \
  -d '{
    "method": "POST",
    "url": "https://api.example.com/agent-action",
    "headers": {"Content-Type": "application/json"},
    "body": "{\"action\": \"transfer\", \"amount\": \"100\"}"
  }'

The tool returns a complete HTTP signature following ERC-8128 specifications, including the signature header that proves the request originated from the agent's wallet address.

Message Verification for Trust Chains

The erc8128-verify-signature tool enables Claude to validate signatures from other agents or services:

# Verify a signature received from another agent
curl -X POST http://127.0.0.1:3100/v1/tools/erc8128-verify-signature \
  -H "Authorization: Bearer wai_sess_<token>" \
  -d '{
    "message": "Agent decision: approve transfer of 100 USDC",
    "signature": "0x1234...",
    "address": "0xabcd..."
  }'

This creates a trust chain where agents can verify each other's communications, essential for multi-agent systems handling financial operations.

Policy Integration for Secure Signing

WAIaaS includes an ERC8128_ALLOWED_DOMAINS policy type from its 21 policy types, allowing administrators to control which domains the agent can sign requests for:

curl -X POST http://127.0.0.1:3100/v1/policies \
  -H "Content-Type: application/json" \
  -H "X-Master-Password: my-secret-password" \
  -d '{
    "walletId": "<wallet-uuid>",
    "type": "ERC8128_ALLOWED_DOMAINS",
    "rules": {
      "domains": ["api.trusted-service.com", "*.verified-agents.io"]
    }
  }'

This prevents agents from signing arbitrary requests to untrusted domains, maintaining security while enabling verified communications.

Real-World Use Cases

These signing capabilities enable several practical scenarios:

Agent-to-Agent Verification: When multiple Claude instances need to coordinate actions, they can sign and verify each other's messages to ensure authentic communication.

Auditable AI Decisions: Financial AI agents can sign their decision rationales, creating an onchain audit trail of why specific trades or investments were made.

Trusted API Integration: Services can verify that API requests actually originated from authorized AI agents, not from malicious actors using stolen credentials.

Cross-Platform Agent Identity: An agent's signatures work across different platforms and services, providing consistent identity verification.

Quick Start with ERC-8128 Signing

Set up WAIaaS with MCP:

npm install -g @waiaas/cli
waiaas quickset --mode mainnet
waiaas mcp setup --all

Configure Claude Desktop with the MCP server configuration above
Test signing in Claude: Ask Claude to "Sign a message saying 'Hello from my AI agent'" and it will use the erc8128-sign-request tool
Verify signatures: Have Claude verify signatures from other agents using the erc8128-verify-signature tool
Set domain policies to control which services your agent can sign requests for

The ERC-8128 standard is still emerging, but WAIaaS provides early implementation allowing developers to experiment with verified AI communications today. As more services adopt ERC-8128 verification, agents with signing capabilities will have significant advantages in trusted interactions.

The combination of WAIaaS's 4 security tiers (INSTANT, NOTIFY, DELAY, APPROVAL) with ERC-8128 signing creates a robust framework where agents can prove their authenticity while maintaining human oversight over critical decisions.

Ready to add cryptographic signing to your Claude agent? Start with the WAIaaS GitHub repository to set up your MCP server, or visit waiaas.ai to explore the full platform. Your AI agent's communications will never be questioned again.