# Security Patterns

Scannable patterns for security code review. Each file has:
- **Rule** — what to do
- **Correct Pattern** — code that works (Python)
- **Incorrect Pattern** — common mistakes
- **Edge Cases** — gotchas

## Patterns

### Fundamentals

| File | Topic |
|------|-------|
| [secure-defaults.md](secure-defaults.md) | Fail closed, deny by default, defense in depth |
| [input-validation.md](input-validation.md) | Allowlist > blocklist, validate at boundaries |
| [credential-handling.md](credential-handling.md) | No hardcoded secrets, environment/secret manager |
| [audit-logging.md](audit-logging.md) | What to log, what not to log |

### Identity

| File | Topic |
|------|-------|
| [authentication.md](authentication.md) | Passwords, tokens, MFA, brute force protection |
| [authorization.md](authorization.md) | Permission checks, IDOR prevention, privilege escalation |

### Attack Prevention

| File | Topic |
|------|-------|
| [injection-prevention.md](injection-prevention.md) | SQL, command, template, path traversal |
| [dos-prevention.md](dos-prevention.md) | Rate limiting, resource bounds, algorithmic complexity |
| [prompt-injection.md](prompt-injection.md) | LLM security, data/instruction separation |

## Sources

- [OWASP Cheat Sheet Series](https://cheatsheetseries.owasp.org/)
- [OWASP Top 10](https://owasp.org/Top10/)
- [OWASP LLM Top 10](https://owasp.org/www-project-top-10-for-large-language-model-applications/)
- [CWE (Common Weakness Enumeration)](https://cwe.mitre.org/)

## Usage

Reference these patterns when building or reviewing systems. Code examples are in Python for universal model comprehension; concepts apply to any language.