Workshop 07 — ArraMQ: SIWE-Authenticated MQTT

The challenge: design an MQTT broker where authentication uses Ethereum wallet signatures instead of passwords.

The Core Idea

Identity lives in the signature — no broker state, no nonce database.

username = "0x<ETH_address>"
password = "<unix_ms>:<topic>:<eip712_sig>"

EIP-712 Typed Data Signing

The key fix over naive approaches: use real EIP-712 (typed data), not EIP-191 (plain message).

const DOMAIN = {
  name: "ArraMQ",
  version: "1",
  chainId: 20260619n,  // Nova chain — prevents cross-chain replay
}

const TYPES = {
  MQTTAuth: [
    { name: "address",   type: "address" },
    { name: "topic",     type: "string"  },  // topic-binding
    { name: "timestamp", type: "uint256" },
  ],
}

Why Topic-Binding Matters

Without topic in the signed body, a malicious broker can take a valid signature for topic/A and forward it for topic/B. With topic in the EIP-712 struct, the signature is cryptographically bound to one topic.

Auth Flow

Client signs: { address, topic, timestamp } → EIP-712 sig
password = "1750419600000:oracle/#:0xdeadbeef..."

Broker webhook (EMQX HTTP auth):
  1. parse ts, topic, sig
  2. |now - ts| < 300s          ← replay window (stateless)
  3. recoverTypedDataAddress() == claimed address
  → allow | deny

What the Cohort Found (Peer Review)

After 14 PRs were reviewed, three patterns emerged across almost all submissions:

Pattern	Issue
EIP-712 vs EIP-191 mislabel	Used `signMessage` but called it “SIWE/EIP-712”
In-memory nonce store	Breaks on restart/horizontal scale
Topic-binding missing	Broker can reroute valid sig to different topic

Tokyo’s v1 proposal had all three issues. v2 fixed all.

Key Learning

Verify before posting. DustBoy ran 26 agents (13 drafts → 13 fact-checks against actual code diffs) before posting review comments. This caught 4 errors that would have been wrong critiques on teammates’ PRs. Draft → verify → post. Never draft → post directly.

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