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securitycritical PriorityID: hybrid-post-quantum-tls-x25519mlkem768-enforcement

Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement

Enforces TLS 1.3 with NIST FIPS 203 hybrid quantum-resistant key encapsulation (X25519MLKEM768) across all ingress edge gateways and network termination layers. Eliminates exposure to Harvest-Now-Decrypt-Later (HNDL) attacks by banning legacy TLS versions and classical-only elliptic curves on perimeter ingress routes.

Prohibited Anti-Pattern: Permitting Classical-Only Key Exchange or Sub-TLS 1.3 Protocols on Ingress Infrastructure

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---
description: Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement - Enforces TLS 1.3 with NIST FIPS 203 hybrid quantum-resistant key encapsulation (X25519MLKEM768) across all ingress edge gateways and network termination layers. Eliminates exposure to Harvest-Now-Decrypt-Later (HNDL) attacks by banning legacy TLS versions and classical-only elliptic curves on perimeter ingress routes.
globs: src/infra/**/*.{ts,js}, src/gateway/**/*.{ts,js}, src/server/**/*.{ts,js}, infra/**/*.ts
alwaysApply: true
verified_by: "agentrules.org"
license: "CC-BY-4.0"
source: "https://agentrules.org/rules/hybrid-post-quantum-tls-x25519mlkem768-enforcement"
---

# Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement

> **Severity**: CRITICAL | **Category**: security
> **Anti-Pattern Warning**: Permitting Classical-Only Key Exchange or Sub-TLS 1.3 Protocols on Ingress Infrastructure

## System Constraints
You are a Principal Security Architect specializing in post-quantum cryptography (PQC) and transport layer security. Your objective is to ensure all edge ingress configurations, TLS listeners, and network transport layers strictly enforce TLS 1.3 and hybrid post-quantum key encapsulation mechanisms (specifically X25519MLKEM768) to mitigate Harvest-Now-Decrypt-Later (HNDL) attacks. Enforce zero tolerance for TLS 1.2 or non-hybrid curve prioritization.

## Strict Guidelines
- Edge listeners MUST set 'minVersion' strictly to 'TLSv1.3'; TLS 1.2 and prior protocols MUST NOT be enabled under any circumstances.
- The supported curve preferences MUST prioritize 'X25519MLKEM768' as the primary key exchange group ahead of classical fallbacks.
- Services MUST NOT fall back to pure unhybridized classical curves (e.g., standalone P-256 or P-384) on high-assurance perimeter routes where quantum secrecy is required.
- Engineers MUST ensure cipher suites adhere to AEAD-only profiles (e.g., TLS_AES_256_GCM_SHA384, TLS_CHACHA20_POLY1305_SHA256, TLS_AES_128_GCM_SHA256).
- Network gateways MUST log key exchange group negotiation metrics to monitor client capability transitions to hybrid post-quantum mechanisms.
- TLS session resumption configurations MUST enforce modern forward secrecy guarantees without degrading the post-quantum posture.

## Bad vs Good Implementations
### TLS Context Configuration for Ingress Gateway Server

#### Bad Antipattern (AI Common Hallucination)
> **Why it fails**: Configuring 'minVersion' as TLSv1.2 allows legacy handshakes vulnerable to HNDL. Omitting the hybrid curve X25519MLKEM768 leaves all asymmetric key exchange sessions decryptable by future cryptanalytically relevant quantum computers (CRQCs).
```typescript
import * as tls from 'node:tls';
import * as fs from 'node:fs';

// Flaw: Allows TLS 1.2 and legacy classical-only key-exchange curves (P-256, pure X25519)
export function createPerimeterSecureContext(): tls.SecureContext {
  return tls.createSecureContext({
    cert: fs.readFileSync('/etc/ssl/certs/ingress.crt'),
    key: fs.readFileSync('/etc/ssl/private/ingress.key'),
    minVersion: 'TLSv1.2',
    ciphers: 'ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384',
    honorCipherOrder: true
  });
}
```

#### Production Standard (Correct)
> **Standard**: Explicitly locks down ingress to TLS 1.3 and enforces 'X25519MLKEM768' as the premier ECDH/KEM negotiation curve in accordance with NIST FIPS 203 ML-KEM requirements.
```typescript
import * as tls from 'node:tls';
import * as fs from 'node:fs';

// Compliant: Restricts protocol to TLS 1.3 and mandates X25519MLKEM768 hybrid key exchange
export function createPerimeterSecureContext(): tls.SecureContext {
  return tls.createSecureContext({
    cert: fs.readFileSync('/etc/ssl/certs/ingress.crt'),
    key: fs.readFileSync('/etc/ssl/private/ingress.key'),
    minVersion: 'TLSv1.3',
    maxVersion: 'TLSv1.3',
    // X25519MLKEM768 is specified as primary; X25519 permitted only as second-order transition fallback
    ecdhCurve: 'X25519MLKEM768:X25519'
  });
}
```
Recommended MCP Servers (mcp-serverlist.com)

Equip agent with system tools to verify code for this stack.

TLS Security Scanner MCP
Inspects and verifies remote TLS ingress endpoints for supported protocol versions, hybrid PQC groups, and cipher suites.
Recommended Agent Skills (askills.dev)

Ready-to-use executable skill functions tailored to this stack.

TestSSL CLI Validator
Command-line suite for testing cipher suites, supported elliptic curves, and post-quantum ML-KEM negotiation support.
Architectural Specification & Invariant Rationale

Architectural Invariant Design: Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement

Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement defines an industrial-grade behavioral standard for security engineering. Enforces TLS 1.3 with NIST FIPS 203 hybrid quantum-resistant key encapsulation (X25519MLKEM768) across all ingress edge gateways and network termination layers. Eliminates exposure to Harvest-Now-Decrypt-Later (HNDL) attacks by banning legacy TLS versions and classical-only elliptic curves on perimeter ingress routes. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Permitting Classical-Only Key Exchange or Sub-TLS 1.3 Protocols on Ingress Infrastructure Without an explicit system instruction file, developers spend hours debugging silent failures.
Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure ModeAI Symptom (The Anti-Pattern)SeverityProduction Impact & Remedy
AI Hallucination & Deprecation DriftPermitting Classical-Only Key Exchange or Sub-TLS 1.3 Protocols on Ingress InfrastructureCritical
Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production.
Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture InconsistencyAI assistants produce mixed paradigms across files, creating fragmented codebase conventions.Medium
Increases cognitive load during code reviews and leads to maintenance debt across engineering teams.
Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.
Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

1

Edge listeners MUST set 'minVersion' strictly to 'TLSv1.3'

Edge listeners MUST set 'minVersion' strictly to 'TLSv1.3'; TLS 1.2 and prior protocols MUST NOT be enabled under any circumstances.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
2

The supported curve preferences MUST prioritize 'X25519MLKEM768' as the primary key exchange group ahead of classical fallbacks.

The supported curve preferences MUST prioritize 'X25519MLKEM768' as the primary key exchange group ahead of classical fallbacks.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
3

Services MUST NOT fall back to pure unhybridized classical curves (e.g., standalone P-256 or P-384) on high-assurance perimeter routes where quantum secrecy is required.

Services MUST NOT fall back to pure unhybridized classical curves (e.g., standalone P-256 or P-384) on high-assurance perimeter routes where quantum secrecy is required.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
4

Engineers MUST ensure cipher suites adhere to AEAD-only profiles (e.g., TLS_AES_256_GCM_SHA384, TLS_CHACHA20_POLY1305_SHA256, TLS_AES_128_GCM_SHA256).

Engineers MUST ensure cipher suites adhere to AEAD-only profiles (e.g., TLS_AES_256_GCM_SHA384, TLS_CHACHA20_POLY1305_SHA256, TLS_AES_128_GCM_SHA256).

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
5

Network gateways MUST log key exchange group negotiation metrics to monitor client capability transitions to hybrid post-quantum mechanisms.

Network gateways MUST log key exchange group negotiation metrics to monitor client capability transitions to hybrid post-quantum mechanisms.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
6

TLS session resumption configurations MUST enforce modern forward secrecy guarantees without degrading the post-quantum posture.

TLS session resumption configurations MUST enforce modern forward secrecy guarantees without degrading the post-quantum posture.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.
Enforcement:Integrated into the Agent Pack rule file. When Cursor, Claude Code, or Codex processes this prompt, it applies this constraint before emitting syntax.
Technical Questions & Answers

Frequently Asked Technical Questions

Common questions developers face when configuring AI coding assistants for this stack:

Q:Why is Strict Hybrid Post-Quantum TLS 1.3 (X25519MLKEM768) Key-Exchange Enforcement critical for AI coding assistants?

Enforces TLS 1.3 with NIST FIPS 203 hybrid quantum-resistant key encapsulation (X25519MLKEM768) across all ingress edge gateways and network termination layers. Eliminates exposure to Harvest-Now-Decrypt-Later (HNDL) attacks by banning legacy TLS versions and classical-only elliptic curves on perimeter ingress routes. Without explicit behavioral boundaries, AI coding assistants (Cursor, Claude Code, Windsurf, Codex) rely on training data averages, which frequently produce deprecated, inefficient, or vulnerable code patterns.

Q:How does adopting this rule prevent AI hallucinations?

This rule explicitly declares what the AI must avoid (Permitting Classical-Only Key Exchange or Sub-TLS 1.3 Protocols on Ingress Infrastructure) and prescribes verified positive examples. Grounding the LLM with negative and positive pairs eliminates guesswork.

Q:Which AI coding environments are supported?

This specification is multi-platform compatible: Cursor (.cursor/rules/*.mdc & .cursorrules), Anthropic Claude Code (CLAUDE.md), Windsurf (.windsurfrules), Codex / Cline (AGENTS.md), and GitHub Copilot (.github/copilot-instructions.md).

Q:Can I combine this rule with other technology stacks?

Yes. Use the Interactive Stack Builder or download an Agent Pack to merge this rule with other frontend, backend, database, security, and DevOps rules without syntax collision.

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