# Security First Design

> Security-First-Design Skill

- Skill: `ilude/security-first-design` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add ilude/security-first-design`
- Raw SKILL.md: https://api.skillmd.com/api/skills/ilude/security-first-design/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: ilude (https://skillmd.com/u/ilude)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/ilude/security-first-design

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# Security-First-Design Skill

**Auto-activate when:** User mentions authentication, authorization, API security, sensitive data, user input, secrets management, encryption, security review, or when working with `.env$` (actual env files, not examples), `credentials.json`, `secrets.yaml`, API keys, authentication systems, or security-critical features.

Systematically evaluate security implications before implementation.

## When to Activate

- Designing new authentication/authorization systems
- Building APIs that handle sensitive data
- Implementing user input handling
- Reviewing security concerns in existing code
- Planning features with security requirements

## Framework

Five-phase security analysis framework:

1. **Attack Surface Mapping** - Identify all external inputs, resource access, privileges, data handling, and authentication needs
2. **Threat Modeling** - Evaluate injection attacks, authentication bypass, authorization bypass, data exposure, and denial of service vectors
3. **Secret Management Audit** - Verify API keys, credentials, .gitignore rules, logging, and encryption
4. **Input Validation Design** - Establish whitelist validation, type/length/format checks, sanitization, and escaping
5. **Security Checklist** - Verify no secrets in code, input validation coverage, least privilege, safe error messages, dependency scanning, and documented risks

## Usage

Apply this framework when security is a primary design concern. Work through phases sequentially, documenting findings and mitigations at each stage.