SINT Protocol

Security, permission, and economic enforcement layer for physical AI.

SINT is the missing governance layer between AI agents and the physical world. Every tool call, robot command, and actuator movement flows through a single Policy Gateway that enforces capability-based permissions, graduated approval tiers, and tamper-evident audit logging.

Academic grounding: SINT is designed with reference to IEC 62443 FR1–FR7, EU AI Act Article 13, and NIST AI RMF. The evaluation framework references the ROSClaw empirical safety study (arXiv:2603.26997) and MCP security analysis (arXiv:2601.17549).

Agent ──► SINT Bridge ──► Policy Gateway ──► Allow / Deny / Escalate
                               │
                       Evidence Ledger (SHA-256 hash-chained)
                               │
                    ProofReceipt (pluggable attestation)

Why SINT?

AI agents can now control robots, execute code, move money, and operate machinery. But there's no standard security layer between "the LLM decided to do X" and "X happened in the physical world."

SINT vs. Other Frameworks

SINT is the only framework purpose-built for physical AI — where actions are irreversible and have real-world consequences. Microsoft AGT targets digital/software agents; SINT targets robots, drones, and actuators.

The empirical case for SINT:

• ROSClaw (IROS 2026): Up to 4.8× spread in out-of-policy LLM action proposals across frontier models under identical safety envelopes. The 3.4× divergence between frontier backends is measurable, reproducible, and persistent.
• MCP security (arXiv:2601.17549): 10 documented real-world MCP breaches in under 8 months, including a CVSS 9.6 command injection affecting 437,000 downloads.
• SROS2: Formally demonstrated to contain 4 critical vulnerabilities at ACM CCS 2022, including access-control bypasses permitting arbitrary command injection.
• Unitree BLE worm (September 2025): Hardcoded crypto keys enabled wormable BLE/Wi-Fi command injection across robot fleets — precisely the scenario SINT's per-agent token scoping and real-time revocation prevent.

Core guarantees:

• No agent action ever bypasses the Policy Gateway (invariant I-G1: No Bypass)
• Every decision is recorded in a tamper-evident SHA-256 hash-chained ledger (invariant I-G3: Ledger Primacy)
• Physical constraints (velocity, force, geofence) are enforced at the protocol level — in the token, not in config
• Tier-gated verifiable compute hooks support provable-execution evidence on critical actions
• E-stop is universal across all non-terminal DFA states (invariant I-G2: E-stop Universality)
• Per-agent capability tokens with real-time revocation

Quick Start

# Prerequisites: Node.js >= 22, pnpm >= 9
pnpm install
pnpm run build
pnpm run test        # full workspace test suite

Start the Gateway Server

pnpm --filter @sint/gateway-server dev
# → http://localhost:3100/v1/health
# → http://localhost:3100/v1/ready
# → http://localhost:3100/v1/docs

Start Production-Like Stacks (One Command)

pnpm run stack:dev
pnpm run stack:edge
pnpm run stack:prod-lite
pnpm run stack:gazebo-validation
pnpm run stack:isaac-sim-validation

Compose profiles:

• docker/compose/dev.yml
• docker/compose/edge.yml
• docker/compose/prod-lite.yml
• docker/compose/gazebo-validation.yml
• docker/compose/isaac-sim-validation.yml

Developer Docs Site (docs.sint.gg)

pnpm run docs:dev
pnpm run docs:build
pnpm run docs:preview

Docs source lives in docs/, VitePress config is in docs/.vitepress/config.mts, and deployment is handled by docs-site.yml.

Community/adoption assets:

• docs/community/discord-launch-runbook.md
• docs/community/discord-launch-kit.md
• docs/community/external-contributor-onboarding.md
• docs/community/good-first-issues-board.md
• docs/community/open-source-collaboration-replies.md
• docs/security-bulletins/2026-04.md

Run a Single Package

pnpm --filter @sint/gate-policy-gateway test
pnpm --filter @sint/bridge-mcp test

SINT Operator Interface

A voice-first, HUD-based control surface for SINT operators. Every command flows through the Policy Gateway.

pnpm run stack:interface  # starts gateway + interface + postgres + redis
# Opens: http://localhost:3202

Features:

• 🎙️ Voice input — Web Speech API (zero external deps), real-time transcript
• 🖥️ Command HUD — 3-panel grid: approvals | action stream | context
• 💾 Operator memory — ledger-backed persistent context (@sint/memory)
• 🔔 Proactive notifications — sint__notify (T2 tier, requires confirmation)
• ✅ T2/T3 approvals — one-click approve/deny with timeout countdown

See docs/guides/sint-interface.md for full setup and usage.

For AI Agents

If you are an AI agent (Claude, GPT, Gemini, Cursor, etc.) working in this repo, read AGENTS.md first. It covers key invariants, common mistakes, and entry points for the most common tasks. For deeper implementation details, see CLAUDE.md.

Architecture

┌──────────────────────────────────────────────────────────────┐
│  AI Agents / Foundation Models                               │
│  (Claude, GPT, Gemini, open-source)                         │
└──────────────────┬───────────────────────────────────────────┘
                   │
┌──────────────────▼───────────────────────────────────────────┐
│  SINT Bridge Layer (L1)                                      │
│  ┌────────────┐ ┌────────────┐ ┌────────────┐ ┌──────────┐  │
│  │ bridge-mcp │ │ bridge-ros2│ │ bridge-a2a │ │ bridge-  │  │
│  │ MCP tools  │ │ ROS topics │ │ Google A2A │ │ open-rmf │  │
│  └────────────┘ └────────────┘ └────────────┘ └──────────┘  │
│  ┌──────────────────────┐ ┌───────────────────────────────┐  │
│  │ bridge-mqtt-sparkplug│ │ bridge-opcua                  │  │
│  │ Industrial IoT       │ │ PLC / OT control plane bridge │  │
│  └──────────────────────┘ └───────────────────────────────┘  │
│  Per-resource state: UNREGISTERED→PENDING_AUTH→AUTHORIZED    │
│  →ACTIVE→SUSPENDED (real-time revocation without restart)    │
└──────────────────┬───────────────────────────────────────────┘
                   │ SintRequest (UUIDv7, Ed25519, resource, action, physicalContext)
┌──────────────────▼───────────────────────────────────────────┐
│  SINT Gate (L2) — THE choke point                           │
│  ┌─────────────────────────────────────────────────────────┐ │
│  │  PolicyGateway.intercept()                              │ │
│  │  1. Schema validation (Zod)                             │ │
│  │  2. Token validation (Ed25519 + expiry + revocation)    │ │
│  │  3. Resource scope check                                │ │
│  │  4. Per-token rate limiting (sliding window)            │ │
│  │  5. Physical constraint enforcement                     │ │
│  │  6. Forbidden action sequence detection                 │ │
│  │  7. Tier assignment: max(BaseTier, Δ_human, Δ_trust...) │ │
│  │  8. T2/T3 → escalate to approval queue                 │ │
│  │  9. T0/T1 + approved T2/T3 → allow                     │ │
│  │  10. Bill via EconomyPlugin (if configured)             │ │
│  └─────────────────────────────────────────────────────────┘ │
│                          ↓                                   │
│  EvidenceLedger (SHA-256 hash chain + ProofReceipt)        │
└──────────────────────────────────────────────────────────────┘

APS vs SINT Primitives

Packages

Gate (Security Core)

Bridges (12 bridges)

Engine (AI Execution Layer)

Reference Capsules

Persistence

Apps & SDKs

Total: 41 workspace members · 1,772 tests passing

Note: Run pnpm test to get the current exact passing test count.

Approval Tiers

Graduated authorization mapped to physical consequence severity:

Tier escalation triggers (Δ factors):

• Δ_human: Human presence sensor active in workspace → +1 tier
• Δ_trust: Agent trust score below threshold or recent failures → +1 tier
• Δ_env: Robot near physical boundary or unstructured environment → +1 tier
• Δ_novelty: Action outside validated distribution (novelty detector) → +1 tier

Formal Specification

Request Lifecycle DFA

SINT models every request as a deterministic finite automaton with 12 states:

IDLE → PENDING → POLICY_EVAL → PLANNING → OBSERVING/PREPARING/ACTING → COMMITTING → COMPLETED
                     ↓                              ↓
                ESCALATING                      ROLLEDBACK  (estop, execution failure)
                     ↓
                  FAILED     (approval denied, timeout)

The ACTING state is only reachable via POLICY_EVAL with a valid token. Physical actuation is structurally impossible without a valid capability token.

Tier Assignment Function

Tier(r) = max(BaseTier(r), Δ_human(r), Δ_trust(r), Δ_env(r), Δ_novelty(r))

Formal Invariants

Benchmark Results

PolicyGateway latency (measured on M3 MacBook Pro, pnpm run bench):

The gateway adds sub-3ms overhead at p99 for all tiers. Run benchmarks: pnpm run bench.

ROS2 control-loop target benchmark:

Industrial benchmark artifacts:

• docs/reports/industrial-benchmark-report.md
• docs/reports/ros2-control-loop-benchmark.md

Compliance mapping assets:

• docs/compliance/tier-crosswalk-pack.md

Key Concepts

Capability Tokens

Ed25519-signed capability tokens — the only authorization primitive. Unlike RBAC (ambient authority to principals), OCap requires explicit token presentation for every operation.

Token fields:

• Resource scoping — what the agent can access (ros2:///cmd_vel, mcp://filesystem/*, a2a://agents.example.com/*)
• Action restriction — what operations are allowed (publish, call, subscribe, a2a.send)
• Physical constraints — max velocity (m/s), max force (N), geofence polygon, time window, rate limit
• Verifiable compute requirements — optional proof type/verifier/freshness/public-input constraints for T2/T3 actions
• Delegation chains — max 3 hops, attenuation only (invariant I-T1)
• Revocation — instant invalidation via revocation store (ConsentPass endpoint)
• W3C DID identity — did:key:z6Mk... format for agent portability

Evidence Ledger

Every policy decision is recorded in a SHA-256 hash-chained append-only log. Chain integrity: ℓ_k.previousHash = SHA256(canonical(ℓ_{k-1})). A gap or hash mismatch constitutes tamper evidence.

Retention policy:

CSML: Composite Safety-Model Latency

A deployment metric that fuses behavioral and physical safety dimensions:

CSML(m, p, t) = α·AR_m + β·BP_m + γ·SV_m - δ·CR_m + ε·𝟙[ledger_intact(t)]

CSML above a deployment threshold θ automatically escalates all subsequent requests from that model backend to the next tier.

Compliance Mapping

IEC 62443 FR1–FR7

EU AI Act Article 13

Tier Crosswalk (NIST AI RMF / ISO 42001 / EU AI Act)

Machine-readable crosswalk endpoint: GET /v1/compliance/tier-crosswalk

API Endpoints

Development Phases

Deployment

Railway (Recommended)

brew install railway
railway login
./scripts/railway-setup.sh
railway variables --set SINT_STORE=postgres SINT_CACHE=redis SINT_API_KEY=$(openssl rand -hex 32)
railway up

Docker Compose

docker-compose up
# Gateway:   http://localhost:3100
# Dashboard: http://localhost:3201
# Postgres:  localhost:5432
# Redis:     localhost:6379

Tech Stack

• Runtime: Node.js 22+
• Language: TypeScript 5.7 (strict mode)
• Monorepo: pnpm workspaces + Turborepo
• HTTP: Hono
• Validation: Zod
• Crypto: @noble/ed25519, @noble/hashes (audited, zero-dependency)
• MCP SDK: @modelcontextprotocol/sdk
• Dashboard: React 19, Vite 6
• Testing: Vitest (run pnpm test for current count)
• Infra: Docker, PostgreSQL 16+, Redis 7, GitHub Actions CI, Railway

Docs & Artifacts

• Protocol spec: docs/SINT_v0.2_SPEC.md
• SIP governance: docs/SIPS.md
• Release notes: docs/RELEASE_NOTES_v0.2.md
• Conformance matrix: docs/CONFORMANCE_CERTIFICATION_MATRIX_v0.2.md
• EU AI Act mapping: docs/compliance/eu-ai-act-mapping.md
• ISO 13482 alignment: docs/compliance/iso-13482-alignment.md
• Formal threat model: docs/security/formal-threat-model.md
• Getting started: docs/getting-started.md
• Deployment profiles: docs/profiles/
• Examples: examples/ (hello-world, warehouse-amr, industrial-cell)
• Multi-language SDKs: sdks/ (TypeScript, Python, Go)
• Operator CLI: apps/sintctl/README.md
• Standalone certification tool guide: docs/guides/standalone-certification-tool.md
• Persistence baseline guide: docs/guides/persistence-baseline.md
• WebSocket approvals guide: docs/guides/websocket-approvals.md
• API docs site guide: docs/guides/api-documentation-site.md
• gRPC bridge guide: docs/guides/grpc-bridge-skeleton.md
• AutoGen interop fixtures guide: docs/guides/autogen-interop-fixtures.md
• AgentSkill delegated authority fixtures guide: docs/guides/agentskill-authz-interop-fixtures.md
• action_ref identity/explainability profile: docs/specs/action-ref-identity-explainability-profile.md
• Payment governance profile (Economic Layer v1): docs/specs/payment-governance-profile-v1.md
• OpenAI Agents SDK governance guide: docs/guides/openai-agents-sdk-integration.md
• Cursor integration guide: docs/guides/cursor-integration.md
• Benchmark report: docs/reports/industrial-benchmark-report.md
• ROS2 loop benchmark report: docs/reports/ros2-control-loop-benchmark.md
• Hardware safety controller roadmap: docs/roadmaps/hardware-safety-controller-integration.md
• Hardware safety handshake fixture: packages/conformance-tests/fixtures/industrial/hardware-safety-handshake.v1.json
• Certification bundle summary: docs/reports/certification-bundle-summary.md
• NIST submission playbook: docs/guides/nist-submission-playbook.md
• NIST submission bundle report: docs/reports/nist-submission-bundle.md

Design Principles

1. Single choke point — Every agent action flows through PolicyGateway.intercept(); no bridge adapter makes authorization decisions independently
2. Result<T, E> over exceptions — All fallible operations return discriminated unions, never throw
3. Attenuation only — Delegated tokens can only reduce permissions, never escalate (I-T1)
4. Append-only audit — The evidence ledger is INSERT-only with SHA-256 hash chain integrity (I-G3)
5. Physical safety first — Velocity, force, and geofence constraints live in the token, not in external config
6. Interface-first persistence — Storage adapters implement clean interfaces; swap in-memory for Postgres/Redis
7. Fail-open on infrastructure — Economy/rate-limit infrastructure failures do not block the safety path
8. E-stop universality — The hardware E-stop bypasses all token checks and is unconditional (I-G2)

References

• ROSClaw: Empirical safety analysis of LLM-controlled physical AI — arXiv:2603.26997 (IROS 2026)
• MCP Security Analysis: Architectural vulnerabilities in the Model Context Protocol — arXiv:2601.17549
• IEC 62443: Industrial automation and control systems cybersecurity standard
• EU AI Act Article 13: Transparency requirements for AI systems
• NIST AI RMF: AI Risk Management Framework
• W3C DID Core: Decentralized Identifiers specification

Roadmap

License

Apache-2.0