docs: add planning document for Issue #365 Additional Security

docs/plans/issue-365-additional-security.md

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+# Issue #365: Additional Security Enhancements
+
+**Status**: Planning
+**Created**: 2025-12-21
+**Issue**: https://github.com/Wikid82/Charon/issues/365
+
+---
+
+## Objective
+
+Implement additional security enhancements to address identified threats and gaps in the current security posture.
+
+## Security Threats to Address
+
+### 1. Supply Chain Attacks ❌ → ✅
+- **Threat:** Compromised Docker images, npm packages, Go modules
+- **Current Protection:** Trivy scanning in CI
+- **Implementation:**
+  - [ ] Add SBOM (Software Bill of Materials) generation
+  - [ ] Enhanced dependency scanning
+
+### 2. DNS Hijacking / Cache Poisoning ❌ → 📖
+- **Threat:** Attacker redirects DNS queries to malicious servers
+- **Implementation:**
+  - [ ] Document use of encrypted DNS (DoH/DoT) in deployment guide
+
+### 3. TLS Downgrade Attacks ✅ → 📖
+- **Threat:** Force clients to use weak TLS versions
+- **Current Protection:** Caddy enforces TLS 1.2+ by default
+- **Implementation:**
+  - [ ] Document minimum TLS version in security.md
+
+### 4. Certificate Transparency (CT) Log Poisoning ❌ → 🔮
+- **Threat:** Attacker registers fraudulent certs for your domains
+- **Implementation:** Future feature (separate issue)
+
+### 5. Privilege Escalation (Container Escape) ⚠️ → 📖
+- **Threat:** Attacker escapes Docker container to host OS
+- **Current Protection:** Docker security best practices (partial)
+- **Implementation:**
+  - [ ] Document running with least-privilege
+  - [ ] Document read-only root filesystem configuration
+
+### 6. Session Hijacking / Cookie Theft ✅ → 🔒
+- **Threat:** Steal user session tokens via XSS or network sniffing
+- **Current Protection:** HTTPOnly cookies, Secure flag, SameSite
+- **Implementation:**
+  - [ ] Verify current cookie implementation
+  - [ ] Add CSP (Content Security Policy) headers
+
+### 7. Timing Attacks (Cryptographic Side-Channel) ❌ → 🔒
+- **Threat:** Infer secrets by measuring response times
+- **Implementation:**
+  - [ ] Audit bcrypt timing
+  - [ ] Use constant-time comparison for tokens
+
+## Enterprise-Level Security Gaps
+
+### In Scope (This Issue)
+- [ ] Security Incident Response Plan (SIRP) documentation
+- [ ] Automated security update notifications documentation
+
+### Out of Scope (Future Issues)
+- Multi-factor authentication (MFA) via Authentik
+- SSO for Charon admin
+- Audit logging for compliance (GDPR, SOC 2)
+- CT log monitoring
+
+## Implementation Phases
+
+### Phase 1: Documentation Updates
+1. Update `docs/security.md` with TLS minimum version
+2. Add container hardening guide
+3. Add DNS security deployment guide
+4. Create Security Incident Response Plan
+
+### Phase 2: Code Changes
+1. Implement CSP headers in backend
+2. Add constant-time token comparison
+3. Verify cookie security flags
+4. Add SBOM generation to CI
+
+### Phase 3: Testing & Validation
+1. Security audit of all changes
+2. Penetration testing documentation
+3. Update integration tests
+
+---
+
+*This document will be updated as planning progresses.*