Lightweight. Outbound-Only. Zero Inbound Attack Surface.

# Agent needs ONLY outbound HTTPS
iptables -A OUTPUT -p tcp --dport 443 -j ACCEPT
iptables -A INPUT -j DROP    # Deny all inbound
iptables -A OUTPUT -j DROP    # Deny all other outbound

// Pseudocode: Agent TLS configuration
tlsConfig := &tls.Config{
    MinVersion: tls.VersionTLS13,
    InsecureSkipVerify: false,
    VerifyPeerCertificate: func(rawCerts [][]byte,
        verifiedChains [][]*x509.Certificate) error {
        // Verify certificate matches pinned hash
        expectedHash := "sha256:a3f8b9c2d1e4..."
        actualHash := sha256(rawCerts[0])
        if actualHash != expectedHash {
            return errors.New("certificate pinning failed")
        }
        return nil
    },
}

{
  "playbook": "disk_cleanup_prod_db",
  "version": "1.4.2",
  "target_host": "prod-db-03",
  "timestamp": "2026-02-10T14:35:43Z",
  "steps": ["..."],
  "signature": "ed25519:a8f3b2c1d9e4f5a6..."
}

func verifyPlaybook(payload Playbook) error {
    // 1. Extract signature
    signature := payload.Signature

    // 2. Verify with control plane public key
    publicKey := loadEmbeddedPublicKey()
    valid := ed25519.Verify(publicKey, payload.Bytes(), signature)
    if !valid {
        return errors.New("invalid signature")
    }

    // 3. Check timestamp freshness (<5 minutes)
    age := time.Now().Sub(payload.Timestamp)
    if age > 5*time.Minute {
        return errors.New("playbook too old, possible replay attack")
    }

    // 4. Verify target host matches
    if payload.TargetHost != agent.Hostname {
        return errors.New("playbook not intended for this host")
    }

    return nil  // All checks passed
}