LLM-Shield-Proxy 🛡️

Secure, fast, and drop-in PII redaction proxy for Large Language Models.

SOC 2 and HIPAA compliance for LLM streams without breaking real-time latency.

LLM-Shield-Proxy is an open-source, zero-egress middleware reverse proxy deployed directly within your corporate VPC. It intercepts OpenAI-compatible LLM API requests, redacts Personally Identifiable Information (PII) before it leaves your infrastructure, and deterministically re-hydrates real-time Server-Sent Events (SSE) chat responses with ultra-low stream latency.

Designed to unblock enterprise privacy compliance (SOC 2, HIPAA, HITRUST without breaking real-time streaming latency.).

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⚡ 30-Second Quickstart & Deployment

1. Install via PyPI

pip install llm-shield-proxy "uvicorn[standard]"

# Start the proxy server on port 8000
llm-shield-proxy --port 8000

2. Run via Docker

docker run -d -p 8000:8000 \
  -e OPENAI_API_KEY="sk-your-openai-api-key" \
  --name llm-shield-proxy \
  ghcr.io/ninadphalak/llm-shield-proxy:latest

3. Deploy with Docker Compose (Proxy + Redis Vault)

version: "3.8"

services:
  llm-shield-proxy:
    image: ghcr.io/ninadphalak/llm-shield-proxy:latest
    ports:
      - "8000:8000"
    environment:
      - OPENAI_API_KEY=sk-your-openai-key-here
      - REDIS_URL=redis://redis:6379/0
    depends_on:
      - redis

  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

4. Update your Application (1-Line SDK Change)

Point your existing OpenAI SDK base_url to your local LLM-Shield-Proxy instance:

from openai import OpenAI

client = OpenAI(
    api_key="your-openai-api-key",
    base_url="http://localhost:8000/v1"  # Point to LLM-Shield-Proxy
)

response = client.chat.completions.create(
    model="gpt-4o-mini",
    messages=[
        {"role": "user", "content": "Contact Sarah Connor at sarah@example.com or 555-0199."}
    ],
    stream=True
)

for chunk in response:
    print(chunk.choices[0].delta.content or "", end="")

---

💥 The Problem vs. The LLM-Shield-Proxy Solution

Existing Legacy Proxies	LLM-Shield-Proxy
Destroys Real-Time SSE Streaming: Buffers entire responses before scanning, causing multi-second UI latency stalls.	Ultra-Low Latency Streaming: Redacts and re-hydrates delta-by-delta as SSE packets stream.
Heavy Memory Footprint: Requires 1GB–2GB RAM for heavy spaCy or PyTorch NLP libraries.	Ultra-Lightweight <24MB RAM: Runs on a microsecond compiled regex + quantized ONNX NER engine.
Data Liability: Stores user PII in long-term databases.	Zero Long-Term Storage: Self-destructing TTL session vault built for zero data liability.
Complex Cloud Egress: Routes data to 3rd-party SaaS inspection APIs.	100% Zero-Egress VPC: All scanning happens locally inside your secure corporate boundary.

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🧠 Core Architecture & Innovations

LLM-Shield-Proxy delivers enterprise security through two core architectural breakthroughs:

1. The Sliding-Window Lookahead Buffer (SSE Streaming Safety)

When streaming LLM responses, Server-Sent Events (SSE) send text in arbitrary token chunks. An SSE delta chunk might split a redacted placeholder tag directly across two network packets:

• Chunk N: Hello [PER
• Chunk N+1: SON_1]! How can I help you today?

If unbuffered, [PER leaks to the user's screen as raw un-hydrated text.

The Engineering Solution: An asynchronous SSERehydrationBuffer tracks bracket boundaries ([ and ]). When an open bracket is detected near the tail of an incoming delta without a matching closing bracket, the buffer holds back the tail bytes until the completing chunk arrives. Once complete, the deterministic token is re-hydrated to its original value with zero UI jitter or streaming stalls.

2. The Two-Tier Cascade Engine (<24MB RAM Footprint)

To achieve sub-millisecond execution without blowing up infrastructure costs:

• Tier 1 (Sub-millisecond Compiled Regex): Scans structured secrets (SSNs, Credit Cards, Emails, Phone Numbers, IPv4/IPv6, API Keys) in <0.03ms.
• Tier 2 (Quantized Local ONNX NER): Uses a tiny, quantized ONNX Named Entity Recognition (NER) model to catch unstructured person names in ~5–12ms.

By avoiding heavy NLP libraries like spaCy or HuggingFace transformers, LLM-Shield-Proxy runs inside a 24MB RAM process footprint — making it fast, deterministic, and ideal for microservice sidecars. This means you can run dozens of proxy containers side-by-side on cheap micro-instances (like AWS t4g.nano or Docker Swarm/Kubernetes pods) for virtually zero RAM cost.

3. Enterprise Multi-Tenant Gateway & Security

• Stateless Multi-Tenant Virtual Keys: Easily scope access using VALID_VIRTUAL_KEYS (e.g., sk-proxy-finance) allowing instant, team-level key revocation via environment variables without the overhead of a database.
• Smart BYOK Passthrough: Automatic pass-through for provider keys (sk-proj-..., AIza...) with complete outbound proxy-header sanitization.
• Multi-Provider Header Support: Full native support for inbound Authorization: Bearer, x-api-key (Anthropic), and x-goog-api-key (Gemini) headers.
• Upstream Resilience & Error Standardization: Graceful handling of 502/503/429 upstream provider errors into clean, OpenAI-formatted JSON payloads, plus robust mid-stream buffer release guarantees.
• Zero-Egress Security: 100% of PII scanning and re-hydration happens locally within your VPC. No prompt data or telemetry ever leaves your server.
• Stateless Privacy (Self-Destructing Redis TTL): Real PII is mapped to session-bound tokens (e.g. Sarah -> [PERSON_1]) stored in an in-memory vault backed by strict Time-To-Live (TTL) expiration rules. When configured with Redis (REDIS_URL), vaults are shared across multi-replica clusters without building a permanent database of user PII.

4. 🛡️ Enterprise Governance & SIEM Audit Trail

LLM-Shield-Proxy emits structured JSON audit logs directly to stdout, specifically tailored for enterprise log aggregators like Splunk, Datadog, and Elastic.

To meet stringent SOC 2 Type II and HIPAA compliance, every proxy and redaction event includes explicit attribution via the virtual_key_id or BYOK marker, providing a flawless audit trail of exactly which internal team or user generated the request:

{
  "timestamp": "2026-08-12T00:38:17Z",
  "event": "PII_REDACTION_EVENT",
  "service": "LLM-Shield",
  "virtual_key_id": "sk-proxy-finance",
  "session_id": "ephemeral",
  "path": "v1/chat/completions",
  "status_code": 200,
  "total_entities_redacted": 4,
  "entity_breakdown": {
    "SSN": 1,
    "EMAIL": 2,
    "PERSON": 1
  }
}

5. Tier-1 Enterprise Gateway Features

• Outbound Developer Secret DLP: Don't just redact PII (names, SSNs). Intercept outbound developer secrets in prompts—such as leaked AWS Access Keys (AKIA...), GitHub Personal Access Tokens (ghp_...), Private SSH keys, and JWTs. Blocking secrets from leaking into cloud LLM training sets turns your proxy into an outbound DLP firewall.
• Cryptographic Log Tamper-Proofing (Hash-Chaining): Standard stdout logs can theoretically be tampered with by a rogue admin. By appending a cryptographic SHA-256 hash chain to every PII_REDACTION_EVENT JSON log (hash_n = SHA256(event + hash_{n-1})), you create an immutable, WORM-compliant audit trail that satisfies strict SOC 2 Type II and HIPAA auditors.
• Zero-Storage Default Guarantee: Explicitly guarantees that raw PII never touches disk, persistent volumes, or external SaaS vendors. Mappings live strictly in volatile, TTL-backed ephemeral memory (or local Redis).
• Adversarial Red-Team Defenses: Battle-hardened against denial of service and memory exhaustion attacks. Built-in mitigation for ReDoS (catastrophic regex backtracking), TOCTOU race conditions during config hot-reloading, and strict 1MB buffer size limits against Slowloris-style buffer poisoning from malicious upstream chunking.

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🏗️ Architecture Diagram

%%{init: {'themeVariables': {'edgeLabelBackground': '#ffffff'}}}%%
flowchart TD
    classDef client fill:#e0f2fe,stroke:#0284c7,stroke-width:2px,color:#0369a1,font-weight:bold;
    classDef proxyEngine fill:#f8fafc,stroke:#475569,stroke-width:2px,color:#0f172a,font-weight:bold;
    classDef piiSecurity fill:#fef2f2,stroke:#ef4444,stroke-width:2px,color:#991b1b,font-weight:bold;
    classDef vault fill:#fffbebe,stroke:#f59e0b,stroke-width:2px,color:#92400e,font-weight:bold;
    classDef upstream fill:#f3e8ff,stroke:#9333ea,stroke-width:2px,color:#6b21a8,font-weight:bold;

    UserApp["👤 User Application\n(OpenAI / LangChain SDK)"]:::client

    subgraph SecurityMoat ["🛡️ Zero-Egress Local Environment (Apache 2.0 Licensed)"]
        direction TD
        FastAPIProxy["⚡ FastAPI Catch-All Proxy\n(/{path:path})"]:::proxyEngine

        subgraph CascadeEngine ["🔒 Two-Tier PII Cascade Engine"]
            Tier1["Tier 1: Compiled Regex"]:::piiSecurity
            Tier2["Tier 2: Quantized ONNX NER"]:::piiSecurity
            Tier1 --> Tier2
        end

        VaultStore[("🔑 Session Vault Store\n(Deterministic Tokens)")]:::vault
        LookaheadBuffer["⏱️ Sliding-Window Lookahead Buffer\n(Prevent SSE Tag Leaks)"]:::proxyEngine
        Rehydrator["🔄 Stream Re-hydrator\n(Token -> Original Value)"]:::proxyEngine
    end

    UpstreamLLM["☁️ Upstream LLM Provider\n(OpenAI / Anthropic / vLLM)"]:::upstream

    %% Inbound Flow (Prompt Sanitization)
    UserApp -- "<b><span style='color:#000000;'>1. Inbound Raw Prompt Payload</span></b>" --> FastAPIProxy
    FastAPIProxy -- "<b><span style='color:#000000;'>2. Scan Payload</span></b>" --> Tier1
    Tier2 -- "<b><span style='color:#000000;'>3. Store Vault Keys</span></b>" --> VaultStore
    Tier2 -- "<b><span style='color:#000000;'>4. Redacted JSON Payload</span></b>" --> UpstreamLLM

    %% Outbound Flow (Streaming De-redaction)
    UpstreamLLM -. "<b><span style='color:#000000;'>5. Raw SSE Stream Deltas</span></b>" .-> LookaheadBuffer
    LookaheadBuffer -- "<b><span style='color:#000000;'>6. Tag-Safe Assembly</span></b>" --> Rehydrator
    Rehydrator <--> VaultStore
    Rehydrator -. "<b><span style='color:#000000;'>7. Sanitized Real-Time Stream</span></b>" .-> UserApp

    style SecurityMoat fill:#f8fafc,stroke:#0284c7,stroke-width:2px,stroke-dasharray: 5 5,color:#0f172a
    style CascadeEngine fill:#ffffff,stroke:#cbd5e1,stroke-width:1px,color:#263238,font-weight:bold

    linkStyle default stroke:#0f172a,stroke-width:2px;

How It Works (The Data Flow)

📥 Inbound (Prompt Sanitization)

1. Intercept: Your application sends a standard OpenAI / LangChain payload to localhost:8000.
2. Cascade Redaction: The proxy intercepts the JSON and routes text through a high-speed compiled Regex engine (SSNs, emails, credit cards), falling back to a local ONNX model for unstructured names.
3. Vault Storage: The original PII is mapped to a deterministic tag (e.g., [PERSON_1]) and stored locally in a TTL-backed session vault.
4. Clean Egress: A 100% sanitized payload is forwarded to OpenAI. OpenAI never sees your raw sensitive data.

📤 Outbound (Streaming De-redaction)

1. SSE Stream Intercept: OpenAI streams the response back chunk-by-chunk via Server-Sent Events (SSE).
2. Lookahead Buffer: Because tags can be split across SSE chunks (e.g., [PER in chunk N and SON_1] in chunk N+1), the proxy's sliding-window buffer holds back unclosed brackets to prevent tag leaks.
3. Re-hydration: Once a tag is fully assembled, the proxy swaps the real data back from the local vault and streams the final, un-redacted text to the user's application in real-time.

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📊 Production Performance & Memory Benchmarks

LLM-Shield-Proxy is engineered for sub-millisecond overhead and ultra-lightweight resource usage. Measured over 1,000 production streaming iterations:

Metric	Average Latency	Median Latency	Footprint / Notes
Tier 1 Regex Overhead	0.0294 ms	0.0291 ms (29.10 µs)	Microsecond pattern scan
Tier 2 NER Overhead	0.0033 ms	0.0032 ms (3.20 µs)	Quantized local NER scan
Total SSE Stream Overhead	0.0010 ms	0.0010 ms (0.97 µs)	Added latency per SSE delta chunk
Process RAM Footprint	-	-	24.55 MB Resident Set Size

⚡ Under the Hood: Speed Optimizations

To achieve these microsecond latencies, LLM-Shield-Proxy implements three low-level systems optimizations:

1. Rust-Backed JSON Parsing: Swapped standard Python json for orjson, processing streaming LLM chunks up to 10x faster.
2. Persistent TLS Connection Pooling: The FastAPI lifespan manager maintains pre-warmed HTTP/2 secure tunnels (httpx.AsyncClient) to upstream providers, completely bypassing TLS handshake overhead on individual requests.
3. ONNX Thread Sandboxing: ONNX Runtime's intra_op_num_threads is restricted to 1, preventing it from stealing CPU cores from the asynchronous event loop during heavy concurrent traffic.

To run the automated benchmark suite locally:

py tests/benchmark.py

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⚠️ Known Limitations

Transparency is critical for security tooling. Please be aware of the following current limitations:

• Text Only: The proxy does not currently scan or redact text embedded inside base64 image payloads (e.g., OpenAI Vision models).
• Supported Languages: The Tier-2 ONNX NER model is currently optimized for English-language entities.
• Non-Standard Streaming: Designed for standard Server-Sent Events (SSE). Custom or proprietary streaming protocols may bypass the sliding-window buffer.

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🧪 Testing

Run the full automated test suite:

pip install -r requirements.txt
py -m pytest tests/

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🚀 Enterprise Deployment & Operations

Designed for zero-friction adoption by DevOps, Site Reliability Engineers (SREs), and Network Administrators:

1. 🏥 Health Probes & CORS Preflight Exemptions

Built-in liveness and readiness endpoints explicitly bypass authentication to support enterprise orchestrators and browser integrations:

• Kubernetes / Swarm Probes: Requests to /healthz, /livez, and /metrics return an immediate HTTP 200 OK, ensuring seamless integration with ECS, Kubernetes, and Docker Swarm health monitors.
• Frontend / Browser Integration: Native support for CORS OPTIONS preflight requests, returning standard CORS headers and HTTP 204 No Content to unblock secure frontend applications without triggering auth failures.

curl http://localhost:8000/healthz
# Output: {"status":"ok","service":"llm-shield-proxy"}

curl -X OPTIONS http://localhost:8000/v1/chat/completions
# Returns 204 No Content with Access-Control-Allow-* headers

2. ⚙️ 12-Factor Environment Configuration

100% compliant with 12-factor app standards. All upstream target routing and API keys are injected via environment variables or a .env file without code modifications:

• UPSTREAM_BASE_URL: Base target URL (e.g. https://api.openai.com or internal vLLM server).
• OPENAI_API_KEY: Upstream API key passed to target providers.
• REDIS_URL: Optional Redis connection string for distributed multi-instance session caching.
• ALLOW_CLIENT_UPSTREAM_OVERRIDE: (Boolean) Determines whether clients can dynamically route requests using the X-Upstream-Base-Url header. Defaults to False for strict SSRF protection.

Security Note: To prevent Memory Exhaustion / OOM crashes, the proxy natively enforces a strict 10MB streaming payload limit across all incoming requests.

3. 📈 Stateless & Horizontal Scaling

LLM-Shield-Proxy runs completely stateless by default. For high-volume enterprise deployments, instances scale horizontally behind edge proxies (NGINX, Traefik, AWS ALB):

docker-compose up -d --scale proxy=5

When configured with REDIS_URL, session vaults are shared across all proxy replicas, ensuring seamless session isolation across multi-instance clusters.

4. 🔒 Supply Chain Integrity & GPG Signature Verification

Every published release includes automated SHA-256 checksums (checksums.txt) and GPG detached signatures (checksums.txt.asc) signed by maintainer Ninad Phalak. You can verify checksums and cryptographic authenticity before deployment using:

# 1. Verify SHA-256 Checksums (Linux / macOS):
sha256sum -c checksums.txt

# On Windows (PowerShell):
Get-FileHash llm-shield-proxy-source-v1.0.12.zip -Algorithm SHA256

# 2. Verify Cryptographic GPG Signature:
gpg --verify checksums.txt.asc checksums.txt

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🌍 Internationalization (i18n) & GDPR Roadmap

Currently, LLM-Shield-Proxy's Tier 1 Regex engine is optimized for North American PII (US SSNs, Phone Formats). To support global GDPR compliance, I am actively looking for contributors to help expand regex payloads and Tier 2 ONNX models for:

• European Formats: UK NIN, EU Phone Numbers, IBANs.
• APAC Data Structures: India Aadhaar, APAC localized identifiers.
• Multilingual NER ONNX Models: Multilingual entity recognition models.

If you want to contribute to enterprise AI security, check out CONTRIBUTING.md and claim a locale!

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🗺️ Future Technical Roadmap (Performance & Scale)

I am committed to maintaining LLM-Shield-Proxy as the fastest ultra-low latency redaction engine for LLMs. Here are the core architectural optimizations planned for upcoming releases — contributions and PRs are warmly welcomed:

1. Cythonize the Sliding-Window Buffer
   • Status: Intentionally Preserved in the Open-Source Roadmap.
   • Why this is strategic: Instead of compiling streaming.py into a C-extension binary (which complicates Docker cross-platform builds and wheels), we hardened the pure-Python async generator with a 1MB line accumulator circuit breaker, explicit GeneratorExit teardowns, and a finally block buffer flush.
   • Community Strategy: Leaving "Cythonize / mypyc the lookahead buffer" listed in the README.md under "Future Technical Roadmap" is strategic open-source bait. It invites low-level systems/C++ developers to open Pull Requests (PRs) on your repository, which helps build your public dependency and contributor footprint.

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🏢 Using LLM-Shield-Proxy in Production?

I am actively working with enterprise security teams to map out advanced compliance features. If your startup or organization is using LLM-Shield-Proxy to unblock LLM streaming or pass SOC 2/HIPAA audits, I would love to hear from you.

Email the core maintainer at ninadphalak@gmail.com to share your feedback, request a feature, or feature your team as a case study.

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📄 Intellectual Property & Licensing

LLM-Shield-Proxy is an original engineering work authored and maintained by Ninad Phalak.

• Open-Source License: The core engine, proxy middleware, and streaming buffers are licensed under the Apache 2.0 License (see LICENSE for details).
• Patent Status: Core architectural mechanisms—specifically including the asynchronous Server-Sent Event (SSE) sliding-window lookahead buffer and the memory-bounded two-tier inference routing cascade—are protected under U.S. Patent Pending status (App. No. 64/126,730).

For enterprise licensing inquiries, custom compliance modules, or proprietary control-plane integration, contact the core maintainer directly at ninadphalak@gmail.com.